Endocrinology Practice Questions

Q: Metyrapone inhibits which of the following enzymes?

11-β-hydroxylase. **Explanation:** **1. Mechanism of Action (Why A is correct):** Metyrapone is a potent inhibitor of the enzyme **11-β-hydroxylase** (*CYP11B1*). This enzyme is responsible for the final step of cortisol synthesis: converting 11-deoxycortisol into cortisol [1]. By blocking this enzyme, metyrapone causes a decrease in plasma cortisol levels. This reduction triggers a compensatory increase in ACTH secretion (via the negative feedback loop), which in turn leads to an accumulation of the precursor **11-deoxycortisol**. **2. Analysis of Incorrect Options:** * **Option B (21-β-hydroxylase):** This enzyme converts Progesterone to 11-deoxycorticosterone (DOC) [3]. Deficiency of this enzyme is the most common cause of Congenital Adrenal Hyperplasia (CAH), but it is not the target of Metyrapone [3]. * **Option C & D:** Since Metyrapone is highly selective for 11-β-hydroxylase, these options are incorrect. **3. Clinical Pearls for NEET-PG:** * **Metyrapone Stimulation Test:** Used to assess the integrity of the Hypothalamic-Pituitary-Adrenal (HPA) axis [2]. In a normal response, blocking cortisol should lead to a rise in ACTH and 11-deoxycortisol. A failure of 11-deoxycortisol to rise suggests pituitary or hypothalamic insufficiency. * **Therapeutic Use:** It is used for the medical management of **Cushing’s Syndrome** (especially when surgery is contraindicated) to control hypercortisolism. * **Side Effects:** Because it blocks the final step of cortisol but not the androgen pathway, it can cause **hirsutism** (due to androgen excess) and **hypertension** (due to the mineralocorticoid effects of accumulated 11-deoxycortisol). * **Pregnancy:** Metyrapone is the drug of choice for treating Cushing’s syndrome in pregnancy.

Q: Lab investigations of a patient show low T4 and elevated TSH. Which of the following is the most likely diagnosis?

Hashimoto's disease. ### Explanation **Core Concept: Primary Hypothyroidism** The laboratory profile of **low T4 (thyroxine)** and **elevated TSH (Thyroid Stimulating Hormone)** is the hallmark of **Primary Hypothyroidism** [1]. In this condition, the thyroid gland itself is failing to produce hormones. Due to the loss of negative feedback on the pituitary gland, TSH secretion increases significantly to compensate [1]. **Why Hashimoto’s Disease is Correct:** Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism in iodine-sufficient regions [1]. It is an autoimmune destruction of the thyroid gland. Because the pathology resides in the gland, T4 is low and TSH is high. **Analysis of Incorrect Options:** * **Graves’ Disease:** This is a cause of *hyperthyroidism*. It presents with **high T4** and **suppressed (low) TSH** due to thyroid-stimulating antibodies [1]. * **Pituitary Failure (Secondary Hypothyroidism):** If the pituitary fails, it cannot produce TSH. Therefore, the labs would show **low T4** and **low or inappropriately normal TSH** [1]. * **Hypothalamic Failure (Tertiary Hypothyroidism):** Similar to pituitary failure, a lack of TRH leads to **low T4** and **low TSH** [1]. **NEET-PG High-Yield Pearls:** * **Most sensitive initial test** for thyroid function: **Serum TSH**. * **Subclinical Hypothyroidism:** Elevated TSH with **normal** Free T4 levels [1]. * **Antibody Marker:** Anti-TPO (Thyroid Peroxidase) antibodies are positive in >90% of Hashimoto’s cases. * **Histology Hint:** Look for **Hurthle cells** (Askanazy cells) and lymphocytic infiltration with germinal centers on biopsy.

Q: A 33-year-old man presents with complaints of polydipsia and polyuria. Physical examination reveals a normal JVP at the sternal angle. Laboratory findings include serum sodium of 150 mEq/L, glucose of 120 mg/dL, and serum osmolality of 315 mOsm/kg. Urine studies show urine sodium of 20 mEq/L and urine osmolality of 260 mOsm/kg. Which of the following drugs is most likely to cause this clinical presentation?

lithium. **Explanation:** The patient presents with the classic triad of **Diabetes Insipidus (DI)**: polyuria, polydipsia, and hypernatremia (150 mEq/L) with high serum osmolality (315 mOsm/kg) and inappropriately dilute urine (260 mOsm/kg). The normal JVP indicates a state of euvolemic hypernatremia, typical of DI [1]. **Why Lithium is correct:** Lithium is the most common cause of **drug-induced Nephrogenic Diabetes Insipidus**. It enters the principal cells of the collecting duct through epithelial sodium channels (ENaC) and inhibits glycogen synthase kinase-3 ̧. This interferes with the action of ADH (Vasopressin) on V2 receptors, preventing the insertion of **Aquaporin-2 channels** into the apical membrane [2]. Consequently, the kidneys cannot concentrate urine despite high serum osmolality. **Why other options are incorrect:** * **Cyclophosphamide, Barbiturates, and Nicotine:** These drugs are associated with **SIADH** (Syndrome of Inappropriate Antidiuretic Hormone). SIADH presents with the exact opposite biochemical profile: hyponatremia, low serum osmolality, and inappropriately concentrated urine [3]. **NEET-PG High-Yield Pearls:** * **Diagnosis:** If urine osmolality remains low after Desmopressin administration, it confirms Nephrogenic DI. If it increases by >50%, it is Central DI [1]. * **Management of Lithium-induced DI:** The drug of choice is **Amiloride**, which blocks ENaC channels, preventing lithium from entering the collecting duct cells. * **Other causes of Nephrogenic DI:** Hypercalcemia, hypokalemia, and drugs like Demeclocycline or Amphotericin B [1].

Q: Conn's disease is characterized by an excess of which hormone?

Aldosterone. **Explanation:** **Conn’s Syndrome** (Primary Hyperaldosteronism) is caused by an aldosterone-secreting adenoma of the adrenal cortex (specifically the *zona glomerulosa*) [2]. **Why Aldosterone is Correct:** Aldosterone is a mineralocorticoid that acts on the distal convoluted tubules and collecting ducts of the kidney. It promotes **sodium and water reabsorption** in exchange for **potassium and hydrogen ion excretion** [1]. Consequently, an excess of aldosterone leads to the classic clinical triad of: 1. **Hypertension** (due to sodium/water retention) 2. **Hypokalemia** (due to potassium wasting) 3. **Metabolic Alkalosis** (due to hydrogen ion loss) **Why Other Options are Incorrect:** * **Adrenaline & Noradrenaline (Options A & D):** These are catecholamines secreted by the adrenal medulla [3]. Excess levels are characteristic of **Pheochromocytoma**, which presents with episodic hypertension, palpitations, and diaphoresis. * **Cortisol (Option B):** Excess cortisol leads to **Cushing’s Syndrome**. While it can cause hypertension, it is also associated with distinct features like truncal obesity, striae, and hyperglycemia [2]. **High-Yield NEET-PG Pearls:** * **Screening Test:** Plasma Aldosterone Concentration (PAC) to Plasma Renin Activity (PRA) ratio. A ratio **>20-30** is highly suggestive. * **Confirmatory Test:** Saline infusion test or Oral salt loading test (failure to suppress aldosterone). * **Gold Standard for Lateralization:** Adrenal Venous Sampling (AVS) to distinguish between a unilateral adenoma (Conn's) and bilateral adrenal hyperplasia [4]. * **Treatment:** Surgical excision for unilateral adenoma; **Spironolactone** (aldosterone antagonist) for bilateral hyperplasia.

Q: Which of the following conditions is associated with pretibial myxedema?

Thyrotoxicosis. **Explanation:** **Pretibial Myxedema** (also known as Thyroid Dermopathy) is a classic extrathyroidal manifestation of **Graves' Disease**, the most common cause of **Thyrotoxicosis** [1]. 1. **Why Thyrotoxicosis is Correct:** The underlying mechanism is autoimmune. In Graves' disease, Thyroid Stimulating Immunoglobulins (TSI) bind to TSH receptors located on fibroblasts in the pretibial dermis [1]. This stimulates the overproduction of glycosaminoglycans (primarily hyaluronic acid). The accumulation of these substances leads to non-pitting edema, skin thickening, and an "orange-peel" (peau d'orange) appearance [2]. It is almost exclusively seen in Graves' thyrotoxicosis and is often associated with Graves' ophthalmopathy [1], [3]. 2. **Why Other Options are Incorrect:** * **Hypothyroidism:** While hypothyroidism is associated with "Generalized Myxedema" (due to systemic deposition of mucopolysaccharides), it does **not** cause the localized, infiltrative dermopathy known as pretibial myxedema. * **Hyperparathyroidism:** This condition involves calcium metabolism (stones, bones, abdominal groans, and psychic moans) and has no pathophysiological link to dermal fibroblast stimulation or TSH-receptor antibodies. **High-Yield Clinical Pearls for NEET-PG:** * **The Graves' Triad:** Hyperthyroidism (Goiter), Ophthalmopathy (Exophthalmos), and Dermopathy (Pretibial Myxedema) [1], [3]. * **Location:** Despite the name, it can occasionally occur on the dorsum of the foot or shoulders, though the pretibial area is most common. * **Biopsy Finding:** Increased dermal hyaluronic acid and chondroitin sulfate. * **Management:** Topical glucocorticoids under occlusive dressings are the first-line treatment for symptomatic cases.

Q: A 25-year-old male reports episodic spells characterized by palpitations, sweating, nervousness, and feelings of anxiety. On examination, the man's blood pressure is 165/95 mm Hg. Plasma norepinephrine is 450 pg/mL (normal, 150-400 pg/mL), plasma epinephrine is 115 pg/mL (normal, 25-100 pg/mL), and 24-hour urinary VMA is 11 mg (normal, < 8 mg). Which of the following is the most likely cause of the patient's hypertension?

Pheochromocytoma. The clinical presentation of episodic palpitations, sweating, anxiety, and hypertension forms the classic triad of **Pheochromocytoma**. This catecholamine-secreting tumor (usually arising from the adrenal medulla) leads to an excess of epinephrine and norepinephrine. The laboratory findings in this case—elevated plasma catecholamines and increased 24-hour urinary Vanillylmandelic acid (VMA)—confirm the diagnosis [2]. VMA is the end-stage metabolite of catecholamines, and its elevation is a high-yield diagnostic marker. **Why the other options are incorrect:** * **11-beta-hydroxylase deficiency:** This form of Congenital Adrenal Hyperplasia (CAH) causes hypertension due to the buildup of 11-deoxycorticosterone (a mineralocorticoid). However, it is typically associated with virilization (excess androgens) and would not cause elevated catecholamines or VMA. * **Conn’s Syndrome (Primary Hyperaldosteronism):** This presents with hypertension and hypokalemia due to excess aldosterone [1]. It does not cause episodic "spells" or elevated urinary VMA. * **Renin-secreting tumor:** This rare tumor leads to secondary hyperaldosteronism. While it causes severe hypertension, it is driven by the Renin-Angiotensin-Aldosterone System (RAAS), not the sympathetic nervous system. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 10s:** 10% are bilateral, 10% are extra-adrenal (Paragangliomas), 10% are malignant, and 10% occur in children. * **Diagnosis:** The most sensitive initial screening test is **Plasma free metanephrines**. 24-hour urinary metanephrines and VMA are highly specific. * **Management:** Always start **Alpha-blockers (e.g., Phenoxybenzamine)** before Beta-blockers to avoid an "unopposed alpha" hypertensive crisis [2]. * **Associations:** Often linked with **MEN 2A/2B**, von Hippel-Lindau (VHL) syndrome, and Neurofibromatosis type 1 [2].

Question 1

A 42-year-old male has a strong positive Benedict's test and random blood sugar > 163 mg%. His fasting blood sugar is > 200 mg%. What is the next line of investigation?

Accepted Answer

Oral glucose tolerance test (OGTT)

Answer

Urine glucose charting hourly

Answer

Repeat Benedict's test

Answer

24-hour urine sugar estimation

Question 2

Metyrapone inhibits which of the following enzymes?

Accepted Answer

11-β-hydroxylase

Answer

21-β-hydroxylase

Answer

Both

Answer

None

Question 3

Lab investigations of a patient show low T4 and elevated TSH. Which of the following is the most likely diagnosis?

Accepted Answer

Hashimoto's disease

Answer

Graves' disease

Answer

Pituitary failure

Answer

Hypothalamic failure

Question 4

Increased serum calcium is seen in all of the following except?

Accepted Answer

Primary hyperparathyroidism

Answer

Myxedema

Answer

Sarcoidosis

Answer

Familial hypocalciuric hypercalcemia

Question 5

Cardiovascular manifestations are more dominant in which of the following conditions?

Accepted Answer

Secondary thyrotoxicosis

Answer

Primary thyrotoxicosis

Answer

Simple goitre

Answer

All of the above

Question 6

A 33-year-old man presents with complaints of polydipsia and polyuria. Physical examination reveals a normal JVP at the sternal angle. Laboratory findings include serum sodium of 150 mEq/L, glucose of 120 mg/dL, and serum osmolality of 315 mOsm/kg. Urine studies show urine sodium of 20 mEq/L and urine osmolality of 260 mOsm/kg. Which of the following drugs is most likely to cause this clinical presentation?

Accepted Answer

lithium

Answer

cyclophosphamide

Answer

barbiturates

Answer

nicotine

Question 7

Conn's disease is characterized by an excess of which hormone?

Accepted Answer

Aldosterone

Answer

Adrenaline

Answer

Cortisol

Answer

Noradrenaline

Question 8

A 40-year-old female with a known history of ischemic heart disease (IHD) is diagnosed with hypothyroidism. Which of the following would be the most appropriate line of management for her?

Accepted Answer

Start levothyroxine at a low dose

Answer

Do not start levothyroxine

Answer

Use levothyroxine

Answer

Thyroid extract is a better option

Question 9

Which of the following conditions is associated with pretibial myxedema?

Accepted Answer

Thyrotoxicosis

Answer

Hypothyroidism

Answer

Hyperparathyroidism

Answer

All of the above

Question 10

A 25-year-old male reports episodic spells characterized by palpitations, sweating, nervousness, and feelings of anxiety. On examination, the man's blood pressure is 165/95 mm Hg. Plasma norepinephrine is 450 pg/mL (normal, 150-400 pg/mL), plasma epinephrine is 115 pg/mL (normal, 25-100 pg/mL), and 24-hour urinary VMA is 11 mg (normal, < 8 mg). Which of the following is the most likely cause of the patient's hypertension?

Accepted Answer

Pheochromocytoma

Answer

11-beta-hydroxylase deficiency

Answer

Conn's syndrome

Answer

Renin-secreting tumor

Endocrinology — MCQs

Endocrinology — MCQs

On this page

Practice by Chapter

Want unlimited practice?