Anil K. Gehi, MD

• Assistant Professor of Medicine
• Section of Cardiac Electrophysiology
• Division of Cardiology
• University of North Carolina School of Medicine
• Chapel Hill, North Carolina

Secondary hyperparathyroidism is typically managed with medical therapy directed at correcting serum calcium and phosphate levels into the physiologic range prehypertension and stress cheapest generic toprol xl uk. Medical therapy consists of a low phosphate diet blood pressure medication names starting with t toprol xl 25 mg buy mastercard, administration of phosphate binders hypertensive encephalopathy order toprol xl 100 mg mastercard, calcium supplementation arteria publicidad order toprol xl with visa, vitamin D supplementation and dialysis arteria3d cartoon medieval pack discount toprol xl 100 mg buy line. These agents are typically added when patients on dialysis fail phosphate binders. Renal transplantation remains the definitive treatment for secondary hyperparathyroidism. However, emerging data suggest that a significant number of patients after renal transplantation still have hyperparathyroidism (Lou et al. Tertiary hyperparathyroidism develops as a result of the persistent stimulation of the parathyroid glands in patients with longstanding secondary hyperparathyroidism. This scenario is most frequently encountered when a patient with renal failure and secondary hyperparathyroidism undergoes renal transplantation. Subtotal Versus Total Parathyroidectomy Surgery is indicated for the management of secondary hyperparathyroidism when medical therapy fails. Additional indications for parathyroid surgery include refractory symptoms of hypercalcemia. Surgical therapy is the primary management of tertiary hyperparathyroidism after renal transplantation. The two accepted operations for the management of secondary and tertiary hyperparathyroidism include subtotal parathyroidectomy and total parathyroidectomy with parathyroid autotransplantation. Despite ongoing debate, neither procedure has been clearly distinguished as superior. The selection of an operative technique remains largely dictated by surgeon preference. Subtotal parathyroidectomy involves identification of all four glands followed by the removal of "three and a half glands. This procedure has the theoretical advantage of less postoperative hypocalcemia because the parathyroid remnant remains in situ and continues to function. One of the disadvantages of a subtotal parathyroidectomy is the need to perform a second cervical exploration for recurrent or persistent hyperparathyroidism, which can be challenging and carries the increased risk of recurrent laryngeal nerve injury. Total parathyroidectomy with autotransplantation involves removal of all four glands followed by selection of the most suitable gland as an autograft. The most normal-appearing gland is chosen and a 40-60 mg portion of this gland is minced into small fragments for autotransplantation. Finally, approximately 10 gland fragments are autotransplanted into an acceptable site, most commonly the brachioradialis muscle of the nondominant forearm. This area should be marked with nonabsorbable or surgical clip in case future surgery is indicated for recurrence. The disadvantages of total parathyroidectomy include temporary post-operative hypocalcemia requiring aggressive medical therapy, risk of autograft failure, and difficulty in removing graft fragments at reoperation. Cryopreservation of the parathyroid tissue is an important adjunct and allows for future autotransplantation in the case of parathyroid transplant failure and persistent hypoparathyroidism. Parathyroid Cancer Parathyroid carcinoma is a very rare malignancy with an incidence of o1 million population per year (Lee et al. Parathyroid carcinoma accounts for less than 1% of cases of primary hyperparathyroidism. Preoperative diagnosis of this malignancy is often challenging as the clinical presentation can mimic that of benign disease. A high index of suspicion should accompany concerning features, including a very high serum calcium (414 mg dLÀ1) and a palpable neck mass. When these features are present, one should consider a metastatic workup prior to exploration. Intraoperatively, the parathyroid gland may appear grayish-white and is often adherent to the surrounding tissue. If parathyroid carcinoma is suspected during the initial procedure, the surgeon should proceed with complete en bloc resection of the tumor with negative margins, including any of the locally invaded tissue such as the contiguous ipsilateral thyroid lobe. In the past, a 158 Parathyroid Surgery central lymph node dissection was recommended, but recent data suggest that this is not necessary for most patients with parathyroid cancer (Hsu et al. Recurrence is best managed with reoperation as surgery is the most effective treatment in palliating the accompanying hypercalcemia. Mortality is usually secondary to the complications of uncontrollable hypercalcemia and not tumor burden. Recurrent and persistence primary hyperparathyroidism occurs more frequently in patients with double adenomas. Calcimimetics for secondary hyperparathyroidism in chronic kidney disease patients. Unilateral versus bilateral neck exploration for primary hyperparathyroidism: a prospective randomized controlled trial. Radioguided parathyroidectomy is equally effective for both adenomatous and hyperplastic glands. A comprehensive evaluation of perioperative adjuncts during minimally invasive parathyroidectomy: Which is most reliable The effectiveness of radioguided parathyroidectomy in patients with negative technetium tc 99m-sestamibi scans. Operative failures after parathyroidectomy for hyperparathyroidism: the influence of surgical volume. A meta-analysis of preoperative localization techniques for patients with primary hyperparathyroidism. The utility of intraoperative bilateral internal jugular venous sampling with rapid parathyroid hormone testing. Cinacalcet normalizes serum calcium in a double-blind randomized, placebo-controlled study in patients with primary hyperparathyroidism with contraindications to surgery. Video-assisted minimally invasive parathyroidectomy: benefits and long-term results. Medical management of primary hyperparathyroidism: Proceedings of the fourth International Workshop on the Management of Asymptomatic Primary Hyperparathyroidism. Parathyroid exploration in the reoperative neck: Improved preoperative localization with 4D-computed tomography. The 20% rule: A simple, instantaneous radioactivity measurement defines cure and allows elimination of frozen sections and hormone assays during parathyroidectomy. Improvement of sleep disturbance and insomnia following parathyroidectomy for primary hyperparathyroidism. Surgeon and staff radiation exposure during radioguided parathyroidectomy at a high-volume institution. Incidence and localization of ectopic parathyroid adenomas in previously unexplored patients. Long-term prospective evaluation comparing robotic parathyroidectomy with minimally invasive open parathyroidectomy for primary hyperparathyroidism. The superiority of minimally invasive parathyroidectomy based on 1650 consecutive patients with primary hyperparathyroidism. A cost-utility analysis to optimize preoperative imaging for primary hyperparathyroidism. Sestamibi imaging for primary hyperparathyroidism: the impact of surgeon interpretation and radiologist volume. The surgical management of asymptomatic primary hyperparathyroidism: Proceedings of the Fourth International Workshop. Hypercalcemia: Other Causes than Primary Hyperparathyroidism René Rizzoli, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland r 2019 Elsevier Inc. Introduction the regulation of calcium homeostasis is aimed at maintaining extracellular calcium concentration and calcium balance as constant as possible, to protect the body against calcium overload and mineral deposition into soft tissues. Extracellular calcium concentration is thus maintained extremely stable, because of the high sensitivity of a variety of cell systems or organs, including the central nervous system, muscle, and exo-/endocrine glands, to small variations of extracellular calcium concentration (Rizzoli and Bonjour, 2006). Calcium homeostasis is controlled by a series of hormones and factors tightly interrelated in complex regulatory systems. The production of some of these agents is regulated by the concentration of the solute they are controlling, through negative feedback mechanisms. Regulation of Extracellular Calcium Concentration Extracellular calcium concentration is maintained in a dynamic equilibrium through fluxes occurring at the level of the intestine, bone and kidney (Rizzoli and Bonjour, 2006). At steady state, as in nongrowing individuals, the amounts of solutes entering the extracellular space are matched by the amounts leaving it. To take into accounts variations in protein or albumin concentrations, when measuring total plasma calcium concentration, various corrections have been proposed. Alternatively, total protein can be used, provided there is no paraprotein, with the formula: Protein-corrected calcemia ¼ measured calcemia/[(protein in g/L/160) þ 0. All the albumin or protein based corrections are not recommended for extreme values of albumin or protein. Indeed, alkalosis is associated with a higher binding of calcium to albumin, hence a lower free calcium concentration. To avoid the problem of the influence of albumin or protein concentration, the golden standard is the determination of the calcium bioactive form, that is, ionized calcium. However, the latter requires strict preanalytical conditions, without any contact of the blood sample with air, and measurement must be completed within 1 h after sampling. From an analytical point of view, ionized calcium determination is performed on blood gas analyzers with a specific electrode, which may complicate its utilization in large series of samples. Such a large volume to be collected in a child may preclude a routine ionized calcium determination in children. Because of the influence of pH on ionized calcium concentration, the latter must be interpreted at native pH, and not after an adjustment for pH 7. Intestinal Fluxes Net intestinal absorption of calcium represents the difference between the amounts of solutes absorbed and secreted into the gut lumen. In human, under normal conditions, fractional calcium intestinal absorption represents approximately 20% of ingested calcium. Net intestinal absorption of calcium depends on dietary intakes, on the capacity of the intestinal wall to transport calcium, on the bioavailability of calcium present in the intestinal lumen, and on the secretory flux. The intestinal calcium active absorptive capacity is mainly controlled by calcitriol, which stimulates the transport through both genomic and nongenomic mechanisms (Rizzoli et al. Parathyroid hormone is not exerting any direct effect on the intestinal cells for calcium absorption, but indirectly through calcitriol. The importance of bioavailability of calcium at absorptive sites is illustrated by the impairment of calcium absorption induced by the formation of complexes with anions, such as phosphate, sulfate, phytate or oxalate. For instance, the colonic mucosa is equipped with a powerful vitamin Dsensitive mechanism of calcium transport. However, the absorption is quantitatively little, since calcium in the large intestine lumen is under a form not available for absorption (Ammann et al. Modification of gut microbiota and lower intestinal content pH can increase distal tract calcium absorption (Ammann et al. At steady state, a 24 h urinary excretion of calcium is mainly the reflection of daily net intestinal calcium absorption. Bone Fluxes In average, about 1% of total bone calcium exchanges every month, through a mechanism involving bidirectional fluxes. The main regulators of these fluxes are parathyroid hormone and calcitriol, as well as numerous factors locally produced (Rizzoli and Bonjour, 2006; Manolagas and Parfitt, 2013; Bonewald, 2017). A large variety of substances either circulating or locally produced, 160 Encyclopedia of Endocrine Diseases, Second Edition, Volume 4 doi:10. In fasting urine, calcium excretion related to creatinine is a direct reflection of net bone calcium exchange (Nordin and Peacock, 1969; Peacock et al. Indeed, after an overnight fast, calcium appearing in the urine mostly originates from bone. Multiplying the calcium to creatinine ratio by serum creatinine provides urinary calcium excretion per glomerular filtration rate unit. Renal Fluxes By controlling calcium excretion, the kidney plays a central role in calcium homeostasis (Rizzoli and Bonjour, 2006). At steady state, the amount of calcium appearing in the urine is the reflection of net fluxes into the extracellular fluid originating from intestine and bone. In proximal tubule, calcium reabsorption is tightly connected to that of sodium (Friedman, 2000). Then, 20% to 30% of filtered calcium are reabsorbed along the loop ascending limb, and 10% at the level of the distal tubule. Parathyroid hormone influences calcium reabsorption in the loop ascending limb and in the distal tubule (Friedman, 2000). Any change in renal tubular capacity to reabsorb calcium is able to induce variations of plasma calcium from 1. This concept has been established by the study of the relationship between urinary calcium excretion and plasma calcium in patients suffering from a lack or an excess of parathyroid hormone. Various situations or pharmacological agents can modulate the renal tubular reabsorption of calcium. Alkalosis stimulates renal tubular reabsorption of calcium, whilst acidosis decreases it. Thiazides and lithium salts increase the reabsorption of calcium, through mechanisms which are independent of parathyroid hormone (Rizzoli et al. Phosphate deficiency, pharmacological doses of calcitonin and loop diuretics are associated with an increase in calcium clearance (Friedman, 2000). Even large variations of the glomerular filtration rate do not cause major changes in calcemia, since the renal tubule can easily maintain the calcium excretion by modulating its reabsorptive capacity.

Unfortunately arrhythmia prevalence toprol xl 100 mg on-line, single items of data of doubtful quality are often brought from this large puzzle of knowledge to the lay press and to dieticians heart attack exo xoxo purchase toprol xl 50 mg amex, and directly applied to the public and to patients heart attack diet purchase toprol xl 25 mg line. However heart attack diet cheap toprol xl 100 mg mastercard, the fact-based physicians and scientists base their knowledge and recommendations exclusively on research data blood pressure ranges pediatrics toprol xl 50 mg purchase with mastercard, even in such a popular domain as nutrition. Even when there is a correlation between bone health and a given nutrient, intakes beyond the physiological needs do not produce a benefit. The nutrient can even have a negative impact by displacing other useful nutrients within the frame of the required caloric intake. On the other hand, any nutritional deficiency results in low bone mass or low bone density, in growth delay during childhood, and in enhanced bone loss in adulthood. Nutritional interventions in deficiency states usually provide positive bone effects, which are difficult to reproduce in states of sufficiency. There are ethnic differences in dietary needs for optimal bone metabolism and bone acquisition; these are not discussed in detail here Dairy Products General Considerations Dairy products, such as milk, yogurt, curd, and cheese, are the best and the most important (but not the only) sources of dietary calcium, at least for Western nutrition. Higher figures were found in more superficial investigations, where minor nutrients, which all contain some calcium, were not included in the analysis. In Asia, dairy products are consumed less and contribute only 20%­23% of the total calcium intake. Some diets with no dairy products, which are meant to lower cholesterol, increase the risk of osteoporosis. A vegan diet is generally poor in calcium, despite the relatively high amount of calcium in certain vegetables and nuts. A Western diet with no dairy products can deliver 250­300 mg calcium or more per day, when special attention is given to mineral water, calcium-rich vegetables, nuts, and seeds in sufficient amounts. As noted, the minimal requirement is set at 800 mg per day, and 1000 mg would not be excessive. In one large survey, milk intake was identified as being associated with mortality. This survey showed that Z3 glasses of milk per day (Z600 mL) was associated with higher mortality in adults and with higher fracture incidence in women (Michaëlsson et al. However, a meta-analysis of 29 prospective cohort studies on milk and mortality did not find such an association (Guo et al. Calcium deficiency disturbs growth and the maintenance of bone mass during adult life, and increases the risk of osteoporosis. In postmenopausal women, the supplementation of a diet with milk improved the nutritional quality of the diet to a greater extent than calcium alone. But compliance to supplements might be better than adherence to milk, and therefore lead to a higher calcium intake. The fear of increasing the cholesterol intake with dairy products concerns only high-fat products, including soft cheeses, butter, and cream. The cholesterol content of a menu of milk, hard cheese, and yogurt providing 1000 mg of calcium has o90 mg cholesterol. Eventual negative cardiovascular effects are due to the content of saturated fatty acids. Bioavailability of Dairy Calcium Calcium from dairy products is highly bioavailable, and well absorbed (20%­30%), but shows individual differences. Its absorption is facilitated by lactose and certain caseino-phospho-peptides, formed during the digestion of milk caseins. The assessment of food intake cannot definitively confirm that it reflects precisely the intake of the tested days, months, or years, and certainly not of the total adult life. In addition, the measurement of the effect on bone is problematic because of confounding factors, including first of all physical activity (known of for many years), but also lower alcohol intake and higher energy intake, which go along with the consumption of milk, or milk consumption during teenage years, which influences the results observed later in life. There are four times more favorable results than negative ones in studies of subjects younger than 30 years, while in older subjects there is no overall effect (Weinsier and Krumdieck, 2000). If one might question the positive bone effects of nutritional calcium, there is no doubt that low calcium intake has a negative effect. First, self-perceived milk intolerance leads to self-imposed reductions in milk consumption, increased bone turnover, and increased risk of fracture, independent of the presence or absence of lactase deficiency. Second, fermented dairy products, such as mature hard and medium hard cheeses, as well as yogurts, do not contain lactose, and can be consumed by those with lactase deficiency. In children In the first 6 months of life, human milk provides adequate amounts of calcium and phosphorus. In another study, women with a high intake during childhood and adolescence had not only a higher bone mass in adulthood, but also a smaller risk of fracture. A review in 2011 revealed that increasing calcium and vitamin D intake in infants and young children above the basic physiological needs had no long-term benefit. This shows again that nutrition has to meet the requirements and to avoid deficiencies, but intake beyond these needs does not offer additional benefits. The age of accelerated growth seems to be especially sensitive to adequate intakes. The bone effect is particularly evident in populations with a low calcium intake such as Asians, where supplementing the diet of children with milk powder or with milk equivalent to 1300 mg calcium enhanced bone accretion. These positive results were opposed by a review that concluded that there is no reason for promoting milk or dairy consumption in children and adolescents (Lanou et al. Nevertheless, the effect of 2 years of school milk intake disappeared after withdrawal, probably because the calcium intake dropped again to low values. In adults the studies searching for a bone effect of nutritional calcium provided contradictory results in adults, except in high-risk populations and in populations with a low calcium intake. Then, in adolescent mothers, dietary calcium was positively associated with the total body calcium of the infants. Finally, in elderly individuals, several studies showed that dairy intake was linked to higher bone density. In general, in the elderly population as well as in children, nutritional calcium is more effective than calcium supplements. However, the sensitivity of this survey was questioned, because it could not reproduce the negative effect of a low intake. Although short intervention trials, using bone markers as outcome, showed positive effects on bone metabolism, many intervention trials with milk, milk powder, and dairy products in adults showed no effect. In an intervention trial, dairy products decreased bone loss in premenopausal women. Positive effects could also be found in postmenopausal Caucasian women and in the elderly. Positive bone effects were especially evident in countries with a low baseline intake of calcium, such as China or Malaysia. Effect of Nutritional Calcium on Fracture Risk In 1988, the protective effect of dietary calcium on the hip fracture risk was suggested by a follow-up study in elderly subjects. Not only the actual intake but also the intake of milk in childhood decreased the risk of fracture in adult women. A meta-analysis of follow-up studies showed the absence of a significant association between milk intake and hip fracture incidence in women. In men, each glass of milk per day was associated with a marginally significant lower risk (Bischoff-Ferrari et al. Although no association between milk and yogurt consumption and hip fracture risk could be found in the Framingham cohort, a year later the same authors found that the hip fracture risk was decreased by 42%, although not significantly, in elderly men and women who consumed regularly milk (Sahni et al. Surprisingly, women had a significant 9% greater risk of hip fracture for every glass of milk consumed per day, whereas no association was observed in men (Michaëlsson et al. This increase of the fracture risk was thought to be due to galactose, because fermented milk and yogurt (all low in galactose) were linked to a significant decrease of the hip fracture risk by 11% per daily serving in women, as could be expected. In addition, cheese, which contains almost no galactose, was also associated with a decrease of the hip fracture risk by 14%. This discrepancy with milk remains mainly unexplained, and shows how difficult it is to assess dietary intakes over a long period. In a recent major study in Caucasian men aged 50 and older, and women past menopause, each additional serving of milk per day was associated with a significant 8% lower risk of hip fracture, as could be expected again. Here milk intake was assessed as a long-term cumulative average, and the intake was updated every 4 years, while in other studies it was assessed only once or twice, which cannot be guaranteed to reflect long-term habits. While the antifracture effect of dairy products is debated, there is no doubt that low calcium intake increases the hip fracture risk (Warensjö et al. One large European survey associated milk consumption with higher fracture risk and higher mortality (Michaëlsson et al. But this could not be confirmed, and was contradicted by a meta-analysis of numerous studies (Soedamah-Muthu et al. There are no intervention trials with dairy products and fracture incidence as an outcome. Only when combined with vitamin D could a small reduction in fracture risk be obtained. Nutrition and Bone Fortified Milk 85 Milk is an excellent carrier of supplemental calcium. Fortified with calcium and given to postmenopausal women over the course of 2 years, it delayed bone loss and decreased resorption markers. Calcium fortification of milk can optimize the calcium intake in infants, when human milk does not meet the requirements. Ice cream fortified with calcium is a convenient vector of alimentary calcium, since it lowered bone resorption. The additional fortification of food with vitamin D, tested in several studies, provided essential results due to vitamin D. Some cheeses that are rich in sodium or in fat, as well as cream or ice cream, may even have a negative effect on bone (Weinsier and Krumdieck, 2000). Yogurt: A small intervention study in postmenopausal women with a low dietary calcium intake of o600 mg per day showed that three servings of yogurt lowered N-telopeptides, a marker of bone resorption, to 22% lower values than the control snack did (Heaney et al. In addition, yogurt contains proteins and phosphorus, which are also important for bone. The additional effect of the probiotics in yogurt, as the promotion of calcium absorption, has only been documented in animal studies. Cheese: Calcium in cheese is as well absorbed as calcium in yogurt, despite the absence of lactose which promotes the absorption of milk calcium. When consumed regularly, these cheeses increase the sodium intake by several grams, which has to be taken into account. In prepubertal girls, cheese had a stronger effect on bone than calcium tablets with vitamin D, and appeared to be more beneficial for cortical bone mass accrual than supplements of calcium with or without vitamin D. Fruits and Vegetables When dairy intake is low, as for example, in Asian countries, calcium content in plants becomes crucial. It is difficult to match the requirements for calcium intake without dairy products in the Western-type diet. By including dairy products, lacto-vegetarians, but not vegans, are able to meet the recommended amounts of calcium. The vegan diet is, on average, low in protein and calcium, and increases the risk of osteoporosis. This negative effect on bone is not more important because of the alkalizing effect of fruits and vegetables, which protects bone (Burckhardt, 2016; Weaver, 2009). The positive effect of fruits and vegetables is also due to the high potassium intake, which lowers calcium excretion. The calcium content of a vegetable does not indicate its nutritional value as a source of calcium. Some substances in vegetables decrease calcium absorption, such as oxalic acid (spinach, collard greens, sweet potatoes, rhubarb, beans) or phytic acid (fibercontaining whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates). This explains, for example, the high availability of calcium in broccoli and kale (40. Other substances enhance calcium absorption, such as lactose and certain caseino-phospho-peptides formed during the digestion of caseins from milk. Nuts and Grain Products Nuts are a natural source of dietary calcium, but they are usually consumed in small amounts. Sesame can be recommended for its exceptionally high calcium content (about 800 mg/100 g). When consumed regularly, they can contribute significantly to the total calcium intake. Tortillas are the second most important source of calcium among Mexican Americans. Soy and Soy Products Soy and some soy products are significant sources of protein (7 38 g 100 gÀ1) and calcium (almost 300 mg calcium 100 gÀ1), although they contain less calcium than dairy products. Their content of oxalate and phytate is variable, and accordingly so is the bioavailability of their calcium. Similar to meat, soy protein contains the essential amino acids, which are lacking in other vegetal protein sources. The intake of fortified soy milk is associated with less osteoporosis, and is comparable to the effect of dairy products. Tofu, a popular soy product, contains about 185 mg calcium 100À1 mg or several times more, depending on the use of calcium sulfate for its coagulation. The great variety of soy or tofu products, all different in their content of calcium and oxalate, excludes general statements. Soy and soy products have a "bone sparing" effect because soy protein is not acidifying, contrary to meat. Meat and Proteins Bone health requires a sufficient protein intake, which is often lacking in populations that are advanced in age and/or malnourished. It contains the essential amino acids, such as soy, which are partially missing in vegetable proteins.

Accordingly low pressure pulse jet bag filter buy genuine toprol xl on-line, it is not uncommon to draw diluted renal blood arteria braquial order toprol xl 25 mg on-line, for example heart attack 3 stents buy 25 mg toprol xl with amex, blood not draining solely from the kidney arrhythmias in children 100 mg toprol xl buy free shipping. Additional problems relate to the fact that (a) multiple renal veins are present in a substantial proportion (20%­28%) of patients on the right side and in much lower (1%­3%) proportion on the left side arteria technologies purchase toprol xl 50 mg online, thus setting the stage for collection of less "pure" renal vein blood on the right than on the left side; (b) the right renal vein is shorter than the left renal vein thus exposing more commonly to admixture of vena cava blood on the right than on the left side; (c) plasma drawn from the lower pole vein might not identify an upper pole (segmental) ischemia and vice versa. Nonsimultaneous Sampling the use of a single catheter for the sampling of both renal veins can expose to the risk of detecting a factitious gradient between the kidneys or sites of sampling if the interventionist is not fast enough, particularly if an abrupt change in renin secretion occurs between the time of sampling on different sides/sites. Therefore, bilateral catheterization with simultaneous blood sampling is advisable unless the time elapsing between sampling from the two sides can be kept within 5 min. Furthermore, it is necessary to avoid any maneuver that can increase abruptly renin secretion, such as stressful stimuli, or administration of drugs (Table 1). With the newer chemiluminescent automated assays of immunoreactive active renin there are several advantages and less variability (Rossi et al. In fact, this assumption may not be verified if renin production is very high as in total renal artery occlusion or renin-producing tumours. According to studies performed at Cornell in the last decades of the last centuries, (Vaughan et al. Conversely, values of the renal venous-arterial renin difference relative to arterial levels from the unaffected (Vctl-Viivc)/Viivc kidney close to zero would indicate absent renin secretion, for example, contralateral suppression. According to these premises, a value of [(Visch-Viivc)/Viivc] þ [(Vctl-Viivc)/Viivc] o0. However, there are several situations in which this simple scheme cannot be applied, such as those with bilateral hemodynamically relevant renal artery obstruction and those with segmental renal artery stenoses. Until then, this lack of information had generated some confusion as regards the optimal cutoff values. Nonetheless, most investigators would now support the concept that lateralization of renin secretion is not a prerequisite for cure of hypertension upon revascularization. Furthermore, they can be safe and effective even in patients for whom surgery is deemed to be contraindicated, such as those with atherosclerotic ostial renal artery stenosis who can be at high risk due to a widespread atherosclerotic involvement. Yet there are patients in whom this issue is still relevant, such as those with unilateral small kidney due to total renal artery occlusion and those with renin-producing tumors. In the latter patients, a clear-cut gradient of renin secretion can be the only clue to the identification of a small tumor. Since the detection of a unilateral small kidney at an abdominal ultrasound in hypertensive patients is not uncommon, these results are of importance for the following reason. The patients with a unilateral small kidney due to renal artery occlusion pose a special challenge from the therapeutic standpoint because, surgical revascularization can be preferred to nephrectomy, in that it provides a preservation of renal function when undertaken in cases with angiographically demonstrated distal reconstitution of the vessels and an evident nephrogram. However, even in these cases revascularization is often unsuccessful, because of coexistence of marked obliterative changes of the intrarenal vascular bed, and leads to a high rate of secondary nephrectomy. On the other hand, primary nephrectomy normalizes blood pressure in the vast majority of the patients with a unilateral small kidney due to total renal artery occlusion. Therefore, they should be performed whenever the clinical picture is suggestive of a small unilateral kidney due to total renal artery occlusion and/ or of a renin producing tumor. Treatment of atherosclerotic renovascular hypertension: Review of observational studies and a meta-analysis of randomized clinical trials. John Loesch, discoverer of Renovascular hypertension, and Harry Goldblatt: Two great pioneers in circulation research. Diagnostic and prognostic value in unilateral renal artery stenosis treated by surgery or percutaneous transluminal angioplasty. Patterns of renal vein renin secretion in patients with renovascular hypertension, and their role in predicting the response to angioplasty. Use of Doppler ultrasonography to predict the outcome of Theraphy for renal-artery stenosis. A renin-secreting tumour with severe hypertension and cardiovascular disease: A diagnostic and therapeutic challenge. Renovascular hypertension with low-to-normal plasma renin: Clinical and angiographic features. Prospective validation of an automated chemiluminescence-based assay of renin and aldosterone for the work-up of arterial hypertension. Renovascular hypertension: Renin measurements to indicate hypersecretion and contralateral suppression, estimate renal plasma flow, and score for surgical curability. Thus, the renin required for local angiotensin production is sequestered from the circulation, that is, is kidney-derived, and the angiotensinogen is derived from the major, if not the only, angiotensinogen-synthesizing organ in the body, that is, the liver. Indeed, current data do not support a contribution of nonhepatic angiotensinogen, for example, in the kidney or adipocytes (Koizumi et al. Therefore, to confirm this rise, renin must be measured directly, for example, with an immunoradiometric assay (Danser and Deinum, 2005). Importantly, renin rises during renin inhibition were found to be substantial, and increases of 4300-fold have been noted (Balcarek et al. These effects depend, at least in part, on their capacity to suppress aldosterone. However, effects on cardiovascular outcome and mortality are similar to that of other classes of antihypertensive drugs (Palmer et al. Moreover, progression toward end stage renal disease is attenuated, but not prevented. Cardiovascular, renal and neurological protective effects of C21 have been reported in various disease models, including stroke, obesity, ischemia­reperfusion injury, pulmonary hypertension, diabetic nephropathy and renal toxicity (Matavelli and Siragy, 2015). Within the kidney, C21 has potent diuretic and natriuretic effects which have been observed in normotensive, hypertensive and diabetic rodents (Kaschina et al. Centrally administered C21 also reduced baroreflex sensitivity in rats with heart failure (Gao et al. However, C21 may be beneficial for end-organ protection in combination with established antihypertensive therapies due to its strong antifibrotic and antiinflammatory effects. Moreover, C21 may be a novel therapy for diseases where fibrosis and/or inflammation are significant aspects of the pathology. C21 has been granted orphan drug status for idiopathic pulmonary fibrosis and has completed stage 1 clinical trials to assess safety, tolerability, pharmacokinetics and pharmacodynamics in healthy men (Steckelings et al. Moreover, these effects were mediated without alterations in blood pressure or heart rate (Haschke et al. However, it is important to note that this study was not powered to detect acute differences in physiology, rather, it was a proof of principle study. Mas receptor agonists Angiotensin-(1­7) has a short plasma half-life and is rapidly degraded in the gastrointestinal tract when given orally. Main effector molecules include A-type (atrial), B-type (brain) and C-type natriuretic peptide, as well as urodilatin. Reinforcement of the natriuretic peptide system is therefore a rational and promising strategy to lower blood pressure and prevent complications in patients with essential hypertension. As a consequence, dual inhibition often caused angioedema due to increases in bradykinin, prompting discontinuation of drug development (Kostis et al. Effects on hemodynamics, sympathetic activity, heart rate variability, and endothelin. Prorenin, renin, angiotensinogen, and angiotensin-converting enzyme in normal and failing human hearts. Selective angiotensin-converting enzyme C-domain inhibition is sufficient to prevent angiotensin I-induced vasoconstriction. Treatment with angiotensin-(1-7) reduces inflammation in carotid atherosclerotic plaques. Activation of central angiotensin type 2 receptors by compound 21 improves arterial baroreflex sensitivity in rats with heart failure. Angiotensin-converting enzyme 2 inhibits lung injury induced by respiratory syncytial virus. Pharmacokinetics and pharmacodynamics of recombinant human angiotensin-converting enzyme 2 in healthy human subjects. Improved insulin sensitivity with angiotensin receptor neprilysin inhibition in individuals with obesity and hypertension. A pilot clinical trial of recombinant human angiotensin-converting enzyme 2 in acute respiratory distress syndrome. Mechanical unloading during left ventricular assist device support increases left ventricular collagen cross-linking and myocardial stiffness. Omapatrilat and enalapril in patients with hypertension: the Omapatrilat Cardiovascular Treatment vs. Proceedings of the National Academy of Sciences of the United States of America 83, 4769­4773. Atrial natriuretic peptide inhibits transforming growth factor beta-induced Smad signaling and myofibroblast transformation in mouse cardiac fibroblasts. Beneficial effects of long-term administration of an oral formulation of angiotensin-(1-7) in infarcted rats. The role of renin-angiotensin system modulation on treatment and prevention of liver diseases. Comparative efficacy and safety of blood pressure-lowering agents in adults with diabetes and kidney disease: A network meta-analysis. Angiotensin receptor neprilysin inhibition in heart failure with preserved ejection fraction. Recombinant angiotensin-converting enzyme 2 improves pulmonary blood flow and oxygenation in lipopolysaccharide-induced lung injury in piglets. Association studies suggest a key role for endothelin-1 in the pathogenesis of preeclampsia and the accompanying reninangiotensin-aldosterone system suppression. Glomerular localization and expression of angiotensin-converting enzyme 2 and angiotensin-converting enzyme: Implications for albuminuria in diabetes. Drug treatment effects on outcomes in heart failure with preserved ejection fraction: A systematic review and metaanalysis. Angiotensin-converting enzyme 2 suppresses pathological hypertrophy, myocardial fibrosis, and cardiac dysfunction. Aldosterone; Synthesis and Metabolism John W Honour, University College London, London, United Kingdom r 2019 Elsevier Inc. Glossary Aldosterone A steroid hormone synthesized in the zona glomerulosa of the adrenal cortex; the major mineralocorticoid in humans. Mineralocorticoid Corticosteroid hormone secreted by the adrenal gland and exerting its function through the mineralocorticoid receptor; also referred to as a hormone that affects water and electrolyte homeostasis. Calcium signaling Is required to maintain intracellular concentrations of calcium. Transfer of calcium ions from the extracellular to the intracellular compartment in both directions alters membrane potential of the cell. Calcium ions can be released from intracellular stores, imported, and exited through membrane ion channels. Introduction the outer layer of the adrenal cortex, the zona glomerulosa, is responsible for the synthesis of aldosterone, although new sites are now recognized, notably adipose, cardiac, and vascular tissues. The glomerulosa cells, when highlighted through specific protein expression, are now seen as small clusters under the capsule rather than what used to be described as a discrete layer. This zona glomerulosa lacks expression of the cytochrome 17a-hydroxylase which is important for cortisol synthesis in the zona fasciculata. The protein also expresses 17,20-lyase activity leading from steroids with 21 carbon atoms to male sex hormones with 19 carbon atoms. Cytochrome P450 enzymes are important in steroidogenesis; these are proteins of about 500 amino acids with a heme group that absorb light at 450 nm (as their name implies) in their reduced states complexed with carbon monoxide. The mechanisms covered in this article have been examined at the molecular genetic level in the search for the basis of primary aldosteronism (see Bandulik, 2017). Cholesterol Aldosterone, like other steroid hormones, is synthesized from cholesterol. There is intracellular trafficking of cholesterol between touching membranes and by cholesterol binding proteins. The mechanisms of cholesterol transfer in adrenal cells are not well understood and further debate is not needed in this review. Further discussion can be found in a comprehensive review on the initial steps of steroid synthesis (Miller, 2017). The benzodiazepine receptor Encyclopedia of Endocrine Diseases, Second Edition, Volume 3 doi:10. Three of these reactions are performed by cytochromes with different cofactor needs. Pregnenolone Steroidogenic acute regulatory protein increases the transfer of cholesterol into the mitochondrial inner membrane where a cytochrome P450 for side chain cleavage (scc) enzyme is located. The conversion of cholesterol to pregnenolone involves 22hydroxylation of cholesterol, 20-hydroxylation of 22R­hydroxycholesterol, and cleavage of the C20 to C22 bond with release of isocaproaldehyde and pregnenolone. Progesterone and Deoxycorticosterone In the endoplasmic reticulum of the zona glomerulosa cells, pregnenolone is converted to progesterone with oxidation of the 3bhydroxyl to a ketone and switch in the double bond in the B-ring to the A-ring by 3b-hydroxysteroid dehydrogenase and D5­D4 isomerase (shift in the double bond from C5 to C4). Exchange between the two genes is common which is the basis for some cases of 21-hydroxylase deficiency. Aldosterone; Synthesis and Metabolism Aldosterone via Corticosterone 533 the actions of a mitochondrial enzyme are required to complete the synthesis of aldosterone. Aldosterone synthesis is mainly controlled by changes of the membrane potential and calcium homeostasis. The cytosolic concentrations of glomerulosa cells are about 100­200 nmol, whereas the extracellular calcium concentration is 1­2 mmol. T type CaV is partially open at resting potential, but the L-type CaV is closed at resting potential and opened at higher levels of membrane depolarization. The specific contributions of these pathways to calcium signaling in glomerulosa cells are largely unknown. Depolarization of the membrane also activates voltage-dependent calcium channels (CaV).

Transthyretin is mostly of liver origin hypertension in pregnancy quality toprol xl 50 mg, but it is also synthesized in pancreatic islet cells blood pressure of 9060 order toprol xl amex, retina arrhythmia medications effective 25 mg toprol xl, and epithelial cells of choroid plexus in both rats and humans hypertension risk factors toprol xl 50 mg buy mastercard. Transthyretin synthesized in the choroid plexus may be important for brain development by maintaining the appropriate T4 concentration in the central nervous system and favoring its uniform distribution in different areas of the central nervous system (Bartalena arteria axilar toprol xl 100 mg order visa, 1990). The single-copy transthyretin gene is located on chromosome 18 and composed of four exons spanning 7. Albumin Albumin is a 66-kDa nonglycosylated protein composed of 585 amino acids (Table 2). It has a relatively strong binding site for thyroid hormone and several additional sites with much lower affinity. Its serum concentration is very high (40 g/L), and the percentage of thyroid hormone bound to albumin is about 20% of T4 and 10% of T3. The single-copy albumin gene is located on the long arm of chromosome 4, linked to vitamin D-binding a2-globulin, whereas in mice the gene is located on chromosome 5, close to the a-fetoprotein gene. There is 90% homology between the human albumin gene and the corresponding gene in rodents. Most automated methods, however, are liable to unpredictable and variable artefacts, which clinicians should be aware of. Lipoproteins Lipoproteins are complex molecules composed of a protein moiety (apolipoprotein) and a lipid (both polar and nonpolar) moiety. The thyroid hormone binding site on apolipoproteins is distinct from the apolipoprotein portion that binds to cell lipoprotein receptors. The physiological role of thyroid hormone binding to lipoproteins is unsettled, but lipoproteins may facilitate enterohepatic circulation, transplacental passage, and central nervous system distribution of thyroid hormones, and they may be involved in thyroid hormone delivery to target tissues with cell surface receptors for apolipoproteins (Benvenga, 2013). Hyperthyroidism and hypothyroidism cause a slight decrease and increase, respectively, in serum thyroxine-binding globulin levels by affecting liver synthesis of the protein. Pregnancy and estrogen therapy cause an increase in serum thyroxine-binding globulin concentrations likely due to the longer half-life of thyroxine-binding globulin in the circulation because of estrogen-induced increased sialylation of the protein. Serum thyroxinebinding globulin values are also increased in patients with acute or chronic hepatitis and in a significant proportion of cases of hepatocarcinoma. Whereas in hepatitis the increase in thyroxine-binding globulin is probably the consequence of thyroxinebinding globulin release from damaged liver cells, in hepatocarcinoma the underlying mechanism may be increased liver synthesis of thyroxine-binding globulin. Patients with nephrotic syndrome have a reduced thyroxine-binding globulin concentration due to massive renal protein loss. Patients with diabetic ketoacidosis often have decreased serum thyroxine-binding globulin levels, which might be related to the lack of stimulation of liver protein synthesis by insulin. Starvation or extreme protein-calorie malnutrition cause a decrease in serum thyroxine-binding globulin concentration likely related to decreased hepatic synthesis of the protein. These effects, as well the decrease in thyroxinebinding globulin that occurs in severe terminal illness, may be mediated by inhibition of thyroxine-binding globulin synthesis caused by interleukin-6. Minor variations in serum thyroxine-binding globulin concentration have been reported in several other pathophysiologic conditions (Table 3). Conversely, administration of androgens, anabolic steroids, glucocorticoids, and L-asparaginase decreases serum thyroxine-binding globulin levels (Table 3) (Bartalena, 1990). Transthyretin the serum transthyretin concentration is often decreased in patients with severe nonthyroidal illness, particularly during proteincalorie malnutrition, nephrotic syndrome, liver diseases, and cystic fibrosis (Table 4). Both decreased liver synthesis of transthyretin (possibly mediated by interleukin-6) and its accelerated degradation contribute to these changes. Transthyretin may be increased in patients with pancreatic endocrine tumors (insulinomas or glucagonomas) or gastrointestinal carcinoids, probably due to transthyretin synthesis by the neoplasm. These changes probably reflect an increased transthyretin synthesis by the choroid plexus. Many drugs affect serum transthyretin concentration, and the effect is often the converse of that on thyroxine-binding globulin. Thus, estrogens decrease serum transthyretin concentration and androgens, anabolic steroids, and glucocorticoids increase serum transthyretin concentrations (Table 4). Although the underlying mechanisms are not completely understood, variations in transthyretin synthesis likely contribute to these changes (Benvenga, 2013). Albumin the albumin concentration is decreased in many acute and chronic nonthyroidal illnesses. Inherited Variations Thyroxine binding globulin Familial forms of thyroxine-binding globulin deficiency and thyroxine-binding globulin excess, both inherited as X-linked traits, exist (Ferrara et al. These defects involve the thyroxine-binding globulin gene rather than the rate of thyroxine-binding globulin disposal. Complete thyroxine-binding globulin deficiency, partial thyroxine-binding globulin deficiency, and thyroxinebinding globulin excess are distinguished according to serum thyroxine-binding globulin levels in hemizygous subjects. In partial thyroxine-binding globulin deficiency, serum thyroxinebinding globulin, concentration in heterozygous females is usually higher than half the normal value. In the presence of excess thyroxine-binding globulin, the serum concentration of the protein is usually two- to fourfold higher than normal. Complete thyroxine-binding globulin deficiency occurs in about 1 in 15,000 newborn males (Refetoff, 1990). In most cases, a single nucleotide substitution, a frameshift due to nucleotide deletion, or multiple nucleotide deletions are the mechanisms leading to early termination of translation and truncation of the thyroxine-binding globulin molecule. Mutations may also occur outside the coding region of the thyroxine-binding globulin gene. Partial thyroxine-binding globulin deficiency is more common and occurs in 1 in 4000 newborns. Some of these variants are unstable, have a reduced binding affinity for T4 and T3, or show an abnormal migration pattern on isoelectric focusing. Inherited thyroxine-binding globulin, excess is rare and occurs in about 1 in 25,000­30,000 newborns. The pathophysiological basis of thyroxine-binding globulin excess has been shown to be thyroxine-binding globulin gene amplification (duplication and triplication), whereas no mutations in the coding and promoting regions have been detected. Transthyretin Many transthyretin variants characterized by single amino acid substitutions have been described, mostly in patients with familial amyloidotic polyneuropathy, amyloidotic cardiomyopathy, or senile systemic amyloidosis (Pappa et al. Some of these transthyretin variants have a reduced binding affinity for thyroid hormone. A different transthyretin variant characterized by an increased affinity for T4 is responsible for a pattern of euthyroid hyperthyroxinemia. Albumin A well-characterized inherited albumin variation transmitted as an autosomal dominant trait is familial dysalbuminemic hyperthyroxinemia, which is characterized by the presence in serum of an albumin variant with increased affinity for thyroid hormones. In many cases, the albumin variant has increased affinity for T4 only; in other instances, an increased affinity for T3 and/ or reverse T3 is also present. Three different single nucleotide substitutions have been identified as the molecular basis for the increased albumin affinity for thyroid hormone. Effects of Variations in Thyroid Hormone-Binding Proteins on Thyroid Function Tests Variations in thyroid hormone-binding protein concentrations or affinity profoundly affect serum total thyroid hormone concentrations. This is particularly true for thyroxine-binding globulin because it has a major role in thyroid hormone binding. Accordingly, a decrease or an increase in the serum thyroxine-binding globulin concentration lead to a decrease or an increase, respectively, in serum total thyroid hormone levels. Although the latter changes are similar to those found in hypothyroidism and hyperthyroidism, respectively, they do not reflect thyroid hypofunction or hyperfunction because they are not associated with variations in the metabolically active, free (unbound) thyroid hormone fraction. Similar considerations are tenable for Familial Dysalbuminemic hyperthyroxinemia and transthyretin-associated hyperthyroxinemia. Therefore, thyroxine-binding globulin excess, familial dysalbuminemic hyperthyroxinemia, and transthyretin-associated hyperthyroxinemia are among the most important causes of euthyroid hyperthyroxinemia. The latter may be independent of thyroid hormone-binding protein variations and caused by drugs. Thus, should serum total thyroid hormone measurement provide results that are in contrast with the clinical picture, a thyroid hormone-binding proteins abnormality should be suspected and searched for. The correct definition of thyroid status requires measurement of serum free thyroid hormones and thyrotropin concentrations. In these circumstances, serum total thyroid hormone levels may be normal in hypothyroid patients, whereas the increased levels of hyperthyroid patients may not easily be distinguished from the increased concentrations due to thyroid hormone-binding protein abnormalities. Table 5 Causes of euthyroid hyperthyroxinemia Thyroxine-binding globulin excess Transthyretin-associated hyperthyroxinemia Familial dysalbuminemic hyperthyroxinemia Amiodarone Propranolol Iodinated contrast agents L-thyroxine therapy Resistance to thyroid hormone Acute phase of psychiatric disorders Serum Thyroid Hormone-Binding Proteins 447 Because serum free thyroid hormone determination is crucial for the assessment of thyroid status and to avoid inappropriate treatment for hyperthyroidism or hypothyroidism, it is essential to select methods for free thyroid hormone measurement that are not affected by the abnormal thyroid hormone-binding protein concentration or affinity. The two-step methods in which free hormone is first separated from protein-bound hormone by dialysis, ultrafiltration, column adsorption chromatography, or immunoadsorption provide the most reliable results. In fact, in the second step (immunoassay) the tracer is not in contact with thyroid hormone-binding proteins, thus preventing interaction between the two and consequent artifactual results. Conclusions Thyroid hormone-binding proteins exert functions that are important for thyroid physiology. They provide a buffering action, preventing abrupt changes in serum thyroid hormone levels; function as a storage system for thyroid hormones; they are involved in targeted delivery of thyroid hormone at the tissue level, thus facilitating thyroid hormone cellular distribution. Both inherited and acquired variations of the major thyroid hormone-binding proteins (thyroxine-binding globulin, transthyretin, and albumin) have been demonstrated. These variations do not modify thyroid status but do affect the results of serum total thyroid hormone measurement and may lead to incorrect diagnosis and inappropriate treatment for hyperthyroidism or hypothyroidism. Thus, for a correct definition of thyroid status, determination of free T4 and T3 by assays that are not influenced by thyroid hormone-binding proteins is required. Thyroid Hormone Receptors Claire Briet, University Hospital of Angers, Angers, France and University of Angers, Angers, France Frédéric Illouz, University Hospital of Angers, Angers, France Patrice Rodien, University Hospital of Angers, Angers, France and University of Angers, Angers, France r 2018 Elsevier Inc. Glossary Cofactor (corepressor or coactivator) Ancillary molecule that binds to the nuclear receptor and dictates the negative or positive response to the receptor. Basically a corepressor binds to an unliganded receptor and is released upon binding of the ligand, which allows for the binding of the coactivator. This can be an homodimerization (two molecules of the thyroid hormone receptor) or an heterodimerization (one molecule of thyroid hormone receptor and one molecule of retinoic acid receptor). Transcription machinery All the molecular complex assembled on the regulatory region of the genes. Dominant negative effect Disturbance of the functioning of the normal receptor (wild-type receptor) by a mutant receptor or an inactive isoform. The thyroid hormones exert their biological effects essentially through a classical pathway grounded by nuclear receptors (Cheng et al. There is also growing evidence of a nonclassical pathway involving membrane receptors (Davis et al. The biological effects of the two pathways are also named genomic effects, a regulation of the expression of target genes on the one hand, and nongenomic effects, usually more rapid effects, on the other hand. Claire Briet, Frederic Illouz and Patrice Rodien participated to the de novo writing of this chapter. This article is an update of Onno Bakker, Thyroid Hormone Receptors, In Encyclopedia of Endocrine Diseases, edited by Luciano Martini, Elsevier, New York, 2004, Pages 490­495. The ligand binding domain, also named the E/F domain, is made of several alpha helixes, delimitating the ligand pocket. The twelfths and last helix can adopt different positions depending on the presence or absence of the ligand. In brief, it moves from a mobile and remote position in absence of ligand to a closer and fixed position and closes the ligand pocket, as the lid of a mouse trap. In addition, by contacting the other parts of the ligand binding domain, it masks the anchoring sites for the corepressors which can no longer bind to the receptor, and contributes to the delineation of the anchoring surface for the coactivators. The ligand binding domain also includes some regions involved in the homo or heterodimerization. Only the three dimensional structure, in models and cristalls, can reconcile all the data by packing remote distant regions together, and building the functional domains. The different isoforms are produced by alternate splicing and different transcription starting sites. Also an additional gene is present on the c-erbA-a locus on the reverse direction, coding for rev-erb a and b, involved in the circadian rythms and metabolic regulations (Kojetin and Burris, 2014). However, the physiological role of such a dominant negative effect in vivo, is not known so far. The liver mainly expresses the b1 receptor, whereas the heart can be seen as an a organ, as well as the brain. This illustrates the redundancy, overlap and possible rescue between the different isoforms. In addition, the availability of the different coactivators and corepressors will modulate the effect of thyroid hormones differently in different cells. Targeting Specific Isoforms for Specific Effects Some biological effects of thyroid hormones, may be sought out in therapeutic. However, the a effects such as the heart and bone response to thyroid hormones, limit their potential use in metabolic disease. There are less data in human models and some concerns on potential liver and cartilage toxicity have emerged (Delitala et al. However, it should be kept in mind that the isoform specificity of these agonists is far from perfect. The organ specificity agonists also relays on tissue diffusion of the agonist (Takahashi and Izuchi, 2016; Trost et al. Along with the design of isoform specific agonists, the design of specific antagonists may be of value (Baxter et al. Proceedings of the National Academy of Sciences of the United States of America 100, 15358­15363. Identification of transcripts initiated from an internal promoter in the c-erb A alpha locus that encode inhibitors of retinoic acid receptor-alpha and triiodothyronine receptor activities. Thyroid hormone analogs for the treatment of dyslipidemia: Past, present, and future. Genetic analysis reveals different functions for the products of the thyroid hormone receptor alpha locus. Increased sensitivity to thyroid hormone in mice with complete deficiency of thyroid hormone receptor alpha. Proceedings of the National Academy of Sciences of the United States of America 98, 349­354. The ability of thyroid hormone receptors to sense t4 as an agonist depends on receptor isoform and on cellular cofactors.

A crucial step for the correct management of these disorders is the early diagnosis arrhythmia symptoms buy toprol xl with visa, the proper differential diagnosis hypertension zone tool order toprol xl mastercard, and hypertension yahoo buy cheapest toprol xl, when appropriate arteria zarzad toprol xl 25 mg purchase, an accurate disease staging arteriogenesis 25 mg toprol xl buy visa. Beyond clinical and laboratory data, different imaging modalities are available to evaluate thyroid disorders. These imaging modalities include both morphological and functional imaging methods, sometimes combined by using hybrid devices. Assessment of Diffuse Thyroid Diseases the thyroid gland is more echo-dense than the adjacent structures. Thyroid volume can be estimated by ellipsoid volume formula applied to each lobe, and a size between 7 and 20 mL can be considered as the normal reference in adult population (Rago et al. The presence of nodules within the gland does not influence the global thyroid function with the exception of autonomously functioning nodules which can be detected by scintigraphy. Remarkably, none of these features is accurate alone and the combination of all features achieves relevance to identify malignant nodules. However, these papers reported retrospective series, and further studies with prospective design are required. Illustrate the presentation of one non-suspicious nodule and one nodule at risk for malignancy. A diffuse increase of parenchymal vascularization is observed at color-Doppler evaluation (right lobe, sagittal section). In a parallel approach the needle is inserted parallel to the probe or at an angle of that: the needle can be viewed as it traverses the nodule. Rarely, papillary cancer has a cystic presentation They may be detected in up to 20% of thyroid cancers. Macrocalcifications do not raise the risk for cancer Rarely, papillary cancers have a halo. There is no a fixed cut-off to define a nodule taller than wide Microcalcifications Is the most specific feature Hypoechoic halo Shape Vascularization Elastography Margins Is the most accurate feature to identify a benign nodule Nodules with taller than wide shape should be viewed as at higher risk A few cancers (up to 20%) have intranodular vascularization. In the vast majority of these cases the relapse of disease occurs in the neck, being frequently discovered in cervical lymph nodes and rarely in the thyroid bed (Haugen et al. Recently, tracers to evaluate the proliferation rate of the thyroid cells became also available. Basically, thyroid scintigraphy may performed by using radiotracers describing the function of follicular cells and radiotracers mapping the proliferative activity of follicular cells, respectively. Tracers Mapping the Function of Follicular Thyroid Cells Normal thyroid tissue is characterized by the unique capability of its follicular cells to trap and to process stable iodine (I) which is subsequently incorporated in thyroglobulin (Tg) in order to form thyroid hormones. Iodine-123 (123I) is an ideal thyroid radiopharmaceutical due to low radiation burden and optimal imaging quality, as opposed to the use of iodine131 (131I), which is strongly discouraged for routine diagnostic use (excepted thyroid cancer management) because of its much higher radiation burden to the thyroid. Importantly, it is not a substrate for any metabolic pathways and a complete washout from thyroid cells occurs in about 30 min. However, although the thyroid does not organify 99mTc-pertechnetate, in the majority of cases the uptake and imaging data provide all the information needed for accurate diagnosis (Giovanella et al. Additionally, it is cheaper and readily available in nuclear medicine departments. As a consequence, it has generally been adopted as the primarily used thyroid tracer in clinical practice (Meller and Becker, 2002). The characteristics of various nuclides used for the visualization of the thyroid gland are shown in Table 4. Instrumentations and Methodology Thyroid scans are obtained by a gamma-camera equipped with a parallel-hole collimator. Sometimes dedicated "pin-hole" collimators are employed to increase focal resolution but a significant geometric distortion should be taken into account in this case. Planar images, acquired in the anterior view for some minutes, provide a reliable map of thyroid function and metabolism. Whole-body scans are obtained by double-head gamma camera to obtain simultaneously anterior and posterior images covering the entire body. In addition to qualitative evaluation of thyroid maps, tracer uptake can be measured by semi-quantitative indexes. Remarkably, the uptake of these tracers is strictly related to the stable I in plasma and any overload of I [due to dietary intake. In addition, medication such as thyroid hormones and anti-thyroid drugs affect the pituitary-thyroid axis and, thereby, the tracer uptake by the thyroid gland. Therefore, a thorough medical history should be obtained prior to administration of the radiopharmaceutical, and interfering drugs should be discontinued for an appropriate period of time. T3: 2 weeks, T4: 4 weeks, anti-thyroid drugs: 3­7 days) and, if necessary, the investigation should be delayed correspondingly. Clinical Applications of Thyroid Scintigraphy Thyroid Imaging with 99m Tc-Pertechnetate and 99m 123 I-Iodide Thyroid scintigraphy, with both Tc-pertechnetate and 123I, reflects the metabolic rate of thyroid cells and are mainly employed to distinguish different causes of hyperthyroidsm and to assess the functional activity of thyroid nodules. In addition it is also performed to detect and locate ectopic thyroid tissue (including the differential diagnosis of congenital hyperthyroidism). Hyperthyroidism the etiology of hyperthyroidism should be determined in order to correctly address the treatment. Thyroid uptake measurements are indicated when the diagnosis is in question (except during pregnancy and usually during lactation) and distinguishes causes of hyperthyroidism having elevated uptake over the thyroid gland. Assessment of the functional activity of thyroid nodules Thyroid autonomy appears as one (unifocal autonomy) or more (multifocal autonomy) hyperactive areas. As a consequence, different indications are given in current clinical guidelines (Haugen et al. Thyroid scintigraphy may also help when evaluating nodules with indeterminate cytology readings. As in very rare cases the appearance of a thyroid nodule may be discordant on radioiodine and pertechnetate scans due to iodide organification defects in the nodule that results in a rapid washout of radioiodine. Congenital hypothyroidism and ectopic thyroid tissue Tc-pertechnetate scan remains the most accurate test for the detection of ectopic thyroid tissue (Noussios et al. Despite new molecular genetic insight into congenital hypothyroidism the 123I or, preferably, 99mTc-pertechnetate scan remains the most accurate test for the detection of ectopic thyroid tissue and the differential diagnosis between thyroid dysgenesis (60­70% of cases), athyreosis (10­30% of cases) and inherited disorders of thyroid metabolism (10­20% of cases) (Meller and Becker, 2002). In particular, thyroid scan is the highly accurate for the detection and location of thyroid dysgenesia while neck ultrasound miss the correct diagnosis in about 50% of cases (De Bruyn et al. Histopathology: multifocal invasive follicular variant of papillary thyroid carcinoma. This test could alter management and potentially benefit outcome as it provides the opportunity of identifying patients with unsuspected regional and distant metastases. Thyroid carcinomas are isointense or slightly hypointense lesions on T1-weighted images and hyperintense lesions on T2-weighted images compared with normal thyroid tissue (Hoanga et al. Other findings suggesting tracheal invasion are deformity of the lumen, focal mucosal irregularity or thickening, and intraluminal mass. In general, these invasive findings preclude the patient from curative surgery and treatment regimen may be changed to a palliative approach (Hoanga et al. Mediastinal dislocation of the lower portions of the thyroid gland with mild tracheal deviation. The most important aggressive subtypes of thyroid cancer are Hürthle cell carcinoma, anaplastic and poorly differentiated thyroid carcinomas. Concordance between thyroid nodule sizes measured by ultrasound and gross pathology examination: Effect on patient management. Neonatal hypothyroidism: Comparison of radioisotope and ultrasound imaging in 54 cases. American Association of Clinical Endocrinologists, American College of Endocrinology, and Associazione Medici Endocrinologi medical guidelines for clinical practice for the diagnosis and management of thyroid nodules. Ultrasonography scoring systems can rule out malignancy in cytologically indeterminate thyroid nodules. Role of isotope scan, including positron emission tomography/computed tomography, in nodular goitre. An ultrasonogram reporting system for thyroid nodules stratifying cancer risk for clinical management. Accuracy of three-dimensional ultrasound for thyroid volume measurement in children and adolescents. Thyroid ultrasonography helps to identify patients with diffuse lymphocytic thyroiditis who are prone to develop hypothyroidism. The continuing importance of thyroid scintigraphy in the era of high-resolution ultrasound. Ectopic thyroid tissue: Anatomical, clinical, and surgical implications of a rare entity. Epidemiology, pathophysiology, guideline-adjusted diagnostics, and treatment of thyroid nodules. Less is more: Reconsidering the need for regular use of diagnostic whole body radioiodine scintigraphy in the follow-up of differentiated thyroid cancer. The newly developed three-dimensional (3D) and two-dimensional (2D) thyroid ultrasound are strongly correlated, but 2D overestimates thyroid volume in the presence of nodules. Thyroid ultrasonography as a tool for detecting thyroid autoimmune diseases and predicting thyroid dysfunction in apparently healthy subjects. Accuracy of international ultrasound risk stratification systems in thyroid lesions cytologically classified as indeterminate. A mathematical formula to estimate in vivo thyroid volume from two-dimensional ultrasonography. Does normal thyroid gland by ultrasonography match with normal serum thyroid hormones and negative thyroid antibodies One in five subjects with normal thyroid ultrasonography has altered thyroid tests. The role of positron emission tomography and positron emission tomography/computed tomography in thyroid tumours: An overview. The role of fluorine-18-fluorodeoxyglucose positron emission tomography in aggressive histological subtypes of thyroid cancer: An overview. The association between hypoechogenicity or irregular echo pattern at thyroid ultrasonography and thyroid function in the general population. Combined (99m)Tc methoxyisobutylisonitrile scintigraphy and fine-needle aspiration cytology offers an accurate and potentially cost-effective investigative strategy for the assessment of solitary or dominant thyroid nodules. Malignancy risk stratification of thyroid nodules: Comparison between the thyroid imaging reporting and data system and the 2014 American Thyroid Association management guidelines. No adverse affect in clinical outcome using low preablation diagnostic (131) activity in differentiated thyroid cancer: refuting thyroid-stunning effect. Thyroid Fine Needle Aspiration Cytology Ivana Kholová, Tampere University, Tampere, Finland Camilla Schalin-Jäntti, Endocrinology, Helsinki University and Helsinki University Hospital, Helsinki, Finland r 2018 Elsevier Inc. A preliminary report by Söderström was published in Acta Medica Scandinavica in 1952. The prevalence of palpable thyroid nodules in iodine-sufficient areas is estimated to 5% in women and 1% in men. When thyroid ultrasound is performed in randomly selected persons, nodules are found in as many as 19%­68%. The aim should be to identify clinically relevant cancers in persons who would benefit from intervention, while avoiding excessive diagnostic procedures in persons who would not benefit from it. Clinical signs and symptoms of hypo- or hyperthyroidism should be registered, as well as possible patient reports of rapid growth of the thyroid/nodule, as well as family history of thyroid disease. Palpation of the thyroid should include an estimate of the size of the thyroid, prevalence of multiple or a single nodules as well as their consistence. Patients with nodules or goiter causing compression symptoms in the neck should be referred for surgery. The Zajdela technique using a bare needle without syringe or a variety of syringe holders for suction technique are used (Table 1). Cellular material is obtained by the cutting action of the trailing edge of the needle and is retained in the needle core by forward motion and capillary tension. Most patients only experience complications similar to those of a blood draw as bleeding, bruising and local pain during the procedure. According to the local practice, samples can be triaged for various stainings and ancillary techniques. The material can also be fixed by 95% ethyl alcohol and cytocentrifuged on slides. Liquid-based preparations concentrate cells into monolayer removing obscuring blood. Cell block refers to the processing of sediment, blood clots, or grossly visible pieces of tissue from cytologic specimens that are processed into paraffin block and stained by hematoxylin-eosin. Cell blocks can be prepared by various techniques, such as plasma-thrombin, agar or histogel techniques. Each category has an implied risk of malignancy and evidence-based clinical management guidelines. This article replaces the one by Armando Bartolazzi, Thyroid Fine Needle Aspiration Cytology, In Encyclopedia of Endocrine Diseases, edited by Luciano Martini, Elsevier, New York, 2004, Pages 430-441. Unsatisfactory smears contain less than six groups of follicular cells with fewer than 10 cells per group. Not preserved or poorly preserved and obscured follicular cells also belong to this category. Benign category results are further sub-classified as benign follicular nodules, thyroiditis, or other less common entities such as acute infection-related inflammation, amyloid goiter, and minocyclinerelated changes. Benign follicular nodule All follicular lesions are a mixture of micro- and macrofollicles. Benign follicular nodule specimen are composed of predominantly macrofollicles, honeycomb clusters and sheets and colloid. The reason is mixed nature of the lesion or contamination by normal thyroid macrofollicles.

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