Endocrinology MCQs Dr Anwar Jammah

Endocrinology MCQs Dr Anwar Jammah

• A 32 -year old women complains of amenorrhea since delivery of a baby 15 months previously, despite the fact that she did not breast feed her baby. The delivery was complicated by excessive hemorrhage that required transfusion of 2. 5 liters of blood. She has also been fatigued and has gained an additional 10 pounds since the baby was born. Laboratory data show the following: Serum LH < id="k. qf"> • • A. Hashimoto's thyroiditis B. Isolated gonadotropin deficiency C. Primary amenorrhea D. Prolactinoma E. Sheehan's syndrome

answer • The correct answer is E. • Sheehan's syndrome is hypopituitarism due to ischemic damage to the pituitary resulting from excessive hemorrhage during parturition. The pituitary is enlarged during pregnancy; it is more metabolically active, and more susceptible to hypoxemia. Furthermore, the blood vessels in the pituitary may be more susceptible to vasospasm because of the high estrogen. In about 30% of women who hemorrhage excessively during parturition, some degree of hypopituitarism eventually becomes manifest. The symptoms depend on how much of the pituitary is damaged and what cell types are destroyed. The patient described above exhibited persistent amenorrhea after delivery of her infant. This is due to destruction of pituitary gonadotrophs and diminished secretion of gonadotropins (LH). There also appears to have been significant destruction of lactotrophs since TRH injection failed to induce an increase in prolactin. Had the women attempted to breast-feed her infant, a failure to lactate mostly likely would have occurred. This case is also characterized by secondary hypothyroidism. The low TSH and failure to respond to TRH injection is confirmatory. Corticotrophs appear to have been spared since plasma ACTH is normal. It is not clear whether somatotrophs were damaged. Further testing would be needed to see if GH reserve is diminished. • • Hashimoto's thyroiditis (choice A) is an autoimmune disorder that produces primary hypothyroidism. Because of diminished negative feedback effects of T 4, serum TSH is usually increased (not decreased). Isolated gonadotropin deficiency (choice B) produces amenorrhea and is associated with low serum LH and estradiol. Hypogonadotropic hypogonadism can occur in female athletes that over-train, in anorexia nervosa, in obesity, or with other emotional or physical stresses. However, other pituitary hormones are unaffected (by definition isolated gonadotropin deficiency only involves a decrease in gonadotropins). Primary amenorrhea (choice C), by definition, means failure of menstrual cycles to ever begin. Since this woman has delivered a baby, primary amenorrhea is highly unlikely. • • A prolactinoma (choice D) is a functional pituitary tumor that secretes excessive prolactin. This can cause amenorrhea by suppressing the Gn. RHpituitary-gonad axis. The patient described above has decreased prolactin secretion.

• A mutation affecting the development of the diencephalon could interfere with the secretion of which of the following hormones? • A. Adrenocorticotrophic hormone (ACTH) B. Epinephrine C. Oxytocin D. Prolactin E. Thyroid stimulating hormone (TSH)

answer • The correct answer is C. The neurohypophysis (posterior pituitary) is derived from an evagination of diencephalic neurectoderm. This structure is responsible for releasing oxytocin and vasopressin to the general circulation. Both hormones are synthesized in cell bodies contained within the hypothalamus. ACTH (choice A), prolactin (choice D), and TSH (choice E) are all synthesized and released by the anterior pituitary, or adenohypophysis, which is derived from an evagination of the ectoderm of Rathke's pouch, a diverticulum of the primitive mouth. Remnants of this pouch may give rise to a craniopharyngioma in later life. Epinephrine (choice B) is synthesized and released into the circulation by the adrenal medulla, a neural crest derivative.

• Which of the following statements is true about thyroid hormone (TH)? A. T 3 is the most active molecule in TH B. Iodine for TH synthesis is taken up by active transport into the thyroid gland C. TH is transported in the blood in proteinbound and free forms. D. All of the above

answer • The correct answer is D The thyroid gland is made up of cells arranged into follicles. Each of these cells takes up inorganic iodine through a Sodium/Iodine symporter. This process in stimulated by TSH. Once the iodine is within the cell, thyroid peroxidase, an apical membrane protein, catalyzes a reaction to organify the iodine and move it into the follicular space (colloid). While in this space, thyroid peroxidase (TPO) also catalyzes a reaction which links two of these molecules together, thus forming T 3 and T 4. These two steps which utilize TPO are important, because they are the site of function for the anti-thyroid medications PTU and methimazole, both of which inactivate TPO. After hormone production, it is kept in the colloid until a stimulus (TSH) induces its release. The hormone is then endocytosed, the excess protein is removed, and then the hormone is secreted into the bloodstream. This release step is also affected by the medication lithium, and when taken chronically, can lead to goiter due to inability to release stored hormone. Thyroid hormones are controlled through a feedback inhibition model, where the final product, T 3, inhibits the release of thyrotropic factors. The initiating factor in the cascade is TRH, which is produced in the hypothalamus. This then stimulates the release of TSH. However, the release of TSH is influenced more by the circulating T 3 levels than the TRH. Once TSH is produced, it then acts at on the thyrocytes directly to stimulate growth, iodine uptake, and colloid endocytosis. Once the colloid is endocytosed and released, it circulates as T 3 and T 4, with 98% of the hormone in circulation being T 4.

• Which of the following statements is/are true regarding PTH? A. Secretion is stimulated by hypocalcemia. B. Secretion is inhibited by hypercalcemia. C. The effect of magnesium on secretion is the same as that of calcium. D. Secretion is stimulated by low 1, 25 -hydroxyvitamin D and inhibited by high levels of 1, 25 -hydroxyvitamin D. E. A, B, and D F. All of the above

Answer • The Correct Answer is D Explanation: PTH, an 84 -amino-acid peptide synthesized and secreted by the parathyroid gland, is a potent regulator of the serum calcium level. Hypocalcemia stimulates the secretion of PTH acutely (with increased PTH synthesis and parathyroid cell hypertrophy and hyperplasia after chronic hypocalcemia), whereas hypercalcemia leads to decreased secretion of PTH. Hypomagnesemia inhibits PTH secretion. Elevated 1, 25 -dihydroxyvitamin D affects PTH synthesis and secretion by directly inhibiting the parathyroid gland indirectly via hypercalcemia. Low levels of 1, 25 -dihydroxyvitamin D have the opposite effect.

• All of the following thyroid conditions are amenable to RAI treatment, except A. Papillary cancer B. Follicular cancer C. Graves' disease D. Thyroid lymphoma E. Multinodular goiter

Answer • The correct answer is D Explanation: Iodine 131 is a radioactive isotope of iodine (RAI) that is selectively concentrated in the thyroid tissue and metabolized by the same pathways as naturally occurring iodine. This, together with its long half-life (8 days), allows it to deliver high doses of radiation to the thyroid gland (βradiation) sufficient to destroy thyroid follicular cells. Thus, 131 I is used in the treatment of Graves' disease, toxic multinodular goiter, and differentiated thyroid cancer. The doses of RAI used in the treatment of Graves' disease and toxic multinodular goiter are relatively low compared with those used in the treatment of thyroid cancer (in which it is used in conjunction with surgery). RAI has no place in the treatment of thyroid lymphoma because lymphoma cells do not concentrate iodine.

• A 27 -year-old white woman was admitted 2 days ago through the emergency room for seizures. She has a history of moderate alcohol use. Two weeks ago she received benzathine penicillin for secondary syphilis. She is complaining of muscle cramps, weakness, and headache. She received 1 g of phenytoin on the day of admission and is now taking 100 mg three times a day. She is also taking acetaminophen, multivitamins, and tapering doses of chlordiazepoxide. There is a history of seizures in her family. She is 5 feet tall and weighs 120 pounds. Her blood pressure is 130/80 mm Hg; pulse is 90 beats/minute. The rest of the physical exam is normal except for a round face, a short neck, short fourth and fifth metacarpals, and bilateral cataracts. Abnormal labs include a calcium of 1. 5 mmol/L (normal range, 2. 2 -2. 6 mmol/L), phosphorus of 1. 7 mmol/L (normal range, 0. 8 -1. 4 mmol/L), and an intact parathyroid hormone (PTH) of 200 pg/m. L (normal range, 15 -65). Which of the following is most likely? A. Hypothyroidism B. Hypogonadism C. Basal ganglia calcification D. Mental retardation E. All of the above

Answer • The correct answer is E Explanation: The findings of Albright's hereditary osteodystrophy (short stature, brachydactyly, and soft tissue calcification) along with severe hypocalcemia and elevated PTH are diagnostic of pseudohyperparathyroidism (Type IA). This is an autosomaldominant disorder resulting from a G protein (Gs) defect, which leads to PTH resistance. Hypothyroidism and ovarian failure also seen because Gs also couples to TSH and gonadotropin receptor signaling, respectively. Mental retardation is seen in 70% of cases.

• A 38 -year-old black woman comes to you for renewal of her medications. She has had hypertension since her last pregnancy at age 30 and has been maintained on clonidine 0. 2 mg twice a day. She gets headaches, dyspnea on exertion, swelling of her feet, and orthopnea but denies chest pain. Her father is also being treated for hypertension. She is married and does not smoke. She is five feet seven inches tall and weighs 257 pounds. Her blood pressure is 180/110 mm Hg; pulse is 92 beats/minute. The rest of her exam is remarkable for hypertensive retinopathy, bibasilar rales, and 1+ pitting edema bilaterally. Initial labs were normal except for a serum potassium of 3. 0 m. Eq/L (normal range, 3. 5 - 5. 0 m. Eq/L) and serum bicarbonate of 33 m. Eq/L (normal range, 22 -28 m. Eq/L). You correct hypokalemia and obtain a random serum aldosterone level of 25 ng/d. L (normal range, 5 -30 ng/d. L) with a plasma renin activity of 0. 5 ng/m. L/hour (normal range, 1. 6 - 7. 4 ng/m. L/hour) while the patient is on a normal diet. What additional tests might be appropriate? A. Adrenal computed tomography (CT) scan B. Adrenal vein sampling C. 18 -hydroxycorticosterone D. Saline loading test E. A, B, and C

Answer • The Correct Answer is E Explanation: Primary aldosteronism, a disorder characterized by hypertension, hypokalemia, suppressed plasma renin activity, and increased aldosterone secretion, affects 0. 05 to 2% of the hypertensive population. This disorder should be suspected in hypertensive patients in whom spontaneous or easily provoked hypokalemia develops that is slow to correct after discontinuation of diuretics. As important as recognizing the presence of primary aldosteronism is the differentiation of lesions that are surgically curable (60 -70% of the cases in some series) from those that are best treated medically. In this patient, the presence of hypertension, hypokalemia, and alkalosis appropriately triggered screening for hyperaldosteronism, which led to the findings of an aldosterone-renin ratio of greater than 30, which constitutes a positive screening test. Aldosteronism can be confirmed by the finding of a 24 -hour urine aldosterone secretion of 12 μg in the salt replete state. Adrenal imaging is the next step to differentiate adrenal adenoma from adrenal hyperplasia, although adenomas smaller than 1. 5 cm can be missed and thus mistaken for hyperplasia. In confusing cases, adrenal vein sampling for aldosterone measurements is used to localize adenoma with a 95% accuracy. The finding of a lateralizing 10: 1 aldosterone ratio in the presence of a symmetrical ACTH-induced cortisol rise diagnoses and localizes an adenoma. Other features suggestive of adenoma include plasma 18 -hydroxy corticosterone of 100 ng/d. L or more, spontaneous hypokalemia of less than 3 m. Eq/L, and an anomalous postural decrease of plasma aldosterone concentration. Saline loading is inappropriate in this patient because of heart failure and hypertensive retinopathy.

• A 35 -year-old black woman comes to see you for a complete physical exam. She has experienced cold intolerance, weakness, and constipation for 3 months. Her menses are regular but scanty. Her history is significant for hypertension and peptic ulcer disease, and her family history includes hypertension and diabetes. The patient is married but has never been pregnant and takes cimetidine 400 mg at bedtime, sustained-release nifedipine 60 mg daily, and docusate sodium 100 mg three times a day. Her pulse is 58 beats/minute with a blood pressure of 135/90 mm Hg. Her skin is dry and scaly, and she has hung-up reflexes. The rest of her exam is normal, and the following labs are obtained: serum chemistries are normal except for a creatine kinase of 300 U/L (normal range, 26 -140 U/L); CBC is normal, free thyroxine (T 4) is 6. 4 pmol/L (normal range, 10 – 22 pmol/L), and thyroid stimulating hormone (TSH) is 1. 5 m. IU (normal range, 0. 3 -5. 0 m. IU). Which of the following tests would you order? A. Free triiodothyronine (T 3) B. Thyroid scan C. Thyroid uptake D. Pituitary magnetic resonance imaging (MRI) E. Antithyroid antibodies

Answer • The Correct Answer is D • Explanation: This patient has central hypothyroidism and should be evaluated for pituitary and end-organ function as well as the presence of a pituitary tumor. The prolactin level should be measured and the pituitary-adrenal, gonadal, and growth hormone axes assessed. The presence of a pituitary tumor can be determined by imaging the pituitary gland with MRI or CT scan. Where appropriate, this should be followed by evaluation of the visual fields. Measurement of the α subunit, a glycoprotein shared by FSH, LH, and TSH, may also be useful because some pituitary tumors secrete only this peptide.

• A 60 -year-old white man comes to see you for chronic back pain, which worsened 1 week ago. He has been wheelchair bound for 6 months because of severe osteoporosis with multiple lumbosacral spine fractures. He has severe asthma, which has required large doses of glucocorticoids for many years. The patient reports progressive loss of height and kyphosis over the past year. Other medications include albuterol and ipratropium inhalers and long-acting theophylline 300 mg twice a day. Significant physical findings include bilateral cataracts, multiple ecchymoses, and a prolonged expiratory phase with bilateral wheezes. Which of the following underlies his osteoporosis? A. Decreased bone formation B. Increased bone loss C. Decreased calcium absorption from the GI tract D. Increased calcium loss in urine E. All of the above

Answer • The correct Answer is E Explanation: Glucocorticoids are used in the treatment of chronic inflammatory diseases of the lungs, connective tissue, and intestines as well as in transplantation because of their anti-inflammatory effect. When long-term treatment is required, several complications (e. g. , cataracts, truncal obesity, skin-thinning, hyperglycemia) may be seen. A particularly disabling complication is bone loss, which can lead to fracture; it can occur with or without the other complications of chronic steroid treatment. The incidence of steroid-induced osteoporosis is unknown, but it appears to be related to the duration of treatment, half-life of the steroid, and its dose. Risk factors associated with increased bone loss include age, body mass index, and duration of use. Steroid-induced osteoporosis proceeds rapidly in the first 6 months of steroid use and slows thereafter. Trabecular bone and the cortical rim of the vertebral body are most susceptible to the effects of steroids. Steroids induce bone loss by several mechanisms. First, they inhibit calcium absorption in the GI tract while enhancing calcium loss in the kidneys. These effects induce secondary hyperparathyroidism, which leads to increased bone resorption. Second, they lower sex hormone levels through an effect on the gonadotropin levels and a direct effect at the gonadal level, as well as by decreasing adrenal sex steroid synthesis by inhibiting ACTH release. Third, they have a direct inhibitory effect on osteoblast proliferation, activity, and half-life, leading to decreased bone formation. Fourth, they induce proximal muscle weakness. Short-term studies showed that steroid-induced osteoporosis can be prevented or treated by using measures aimed at minimizing the negative effects of steroids on calcium and bone metabolism. Deficiency of sex steroids should be corrected. Physical therapy should be encouraged to prevent steroid-induced myopathy. Calcium and vitamin D supplementation and diuretics have been used to enhance calcium absorption and minimize calcium loss in urine, thereby preventing secondary hyperparathyroidism. Regular monitoring is recommended to prevent hypercalcemia.

• A 60 -year-old white man comes to see you for chronic back pain, which worsened 1 week ago. He has been wheelchair bound for 6 months because of severe osteoporosis with multiple lumbosacral spine fractures. He has severe asthma, which has required large doses of glucocorticoids for many years. The patient reports progressive loss of height and kyphosis over the past year. Other medications include albuterol and ipratropium inhalers and long-acting theophylline 300 mg twice a day. Significant physical findings include bilateral cataracts, multiple ecchymoses, and a prolonged expiratory phase with bilateral wheezes. Which of the following measures may be helpful? A. Testosterone replacement (only if he is deficient) B. Physical therapy C. Vitamin D replacement (only if his vitamin levels are low) D. Calcium supplementation E. Hydrochlorothiazide F. All of the above

Answer • The correct Answer is F

• A 38 -year-old black woman draws your attention to a swelling in her neck, which she noticed 2 days ago. She denies palpitations, diaphoresis, and weight loss. There is no pain, hoarseness, or dysphagia. Her medical history is notable only for hypertension. Medications include only atenolol 50 mg once daily. On exam, blood pressure is 150/80 mm Hg; pulse is 70. There is a 2 × 1 -cm nontender nodule on the right lobe of the thyroid. No lymphadenopathy is detected. The remainder of the exam is unremarkable. Electrolytes, blood urea nitrogen (BUN), creatinine, liver function tests, calcium, phosphorus, and CBC are normal. What would you do next? A. Elicit history of head and neck irradiation. B. Elicit a family history of thyroid cancer. C. Obtain thyroid function tests. D. Perform fine-needle aspiration. E. All of the above

Answer • The Correct Answer is E Explanation: The clinically apparent (>1 cm) thyroid nodule is a common clinical finding; up to 5% of the population is affected. It is more common in women than in men, and a majority (85%) are hypofunctional or cold nodules. The likelihood of malignancy in a solitary thyroid nodule is low (4%); cold nodules carry a higher risk than hot nodules (20% vs. 1%). Evaluation of a solitary nodule should be aimed at detecting potentially malignant lesions so that as many cancers are removed with as few operations as possible. A history of head and neck irradiation raises the likelihood that a thyroid nodule is malignant, as does the presence of a family history of differentiated thyroid cancer or medullary cancer of the thyroid (which can be a component of multiple endocrine neoplasia "MEN" type IIA or IIB). Fine-needle aspiration of the thyroid gland is a cost-effective procedure with a high sensitivity and specificity for malignancy. Fine-needle aspiration allows the nodule to be characterized cytologically as benign, malignant, suspicious for malignancy, or indeterminate.