Endocrinology Practice Questions

Q: Thyrotoxic periodic paralysis leads to extreme muscle weakness due to?

Hypokalemia. **Thyrotoxic Periodic Paralysis (TPP)** is a rare but life-threatening complication of hyperthyroidism characterized by sudden episodes of extreme muscle weakness and **hypokalemia**. **Why Hypokalemia is the correct answer:** The pathophysiology involves an intracellular shift of potassium rather than a total body deficit. Excess thyroid hormones increase the activity of the **Na+/K+-ATPase pump**, which drives potassium from the extracellular fluid into the muscle cells. This leads to hyperpolarization of the muscle membrane, making it non-excitable and resulting in acute flaccid paralysis. This shift is often triggered by high carbohydrate meals (insulin also stimulates the Na+/K+ pump) or strenuous exercise. **Why other options are incorrect:** * **Hypocalcemia:** Typically presents with tetany, carpopedal spasm, and Chvostek/Trousseau signs, rather than periodic flaccid paralysis. * **Hypomagnesemia:** Often co-exists with hypokalemia but is not the primary driver of the paralytic episodes in thyrotoxicosis. * **Hyponatremia:** Usually presents with neurological symptoms like confusion, seizures, or coma due to cerebral edema, not focal or global muscle paralysis. **High-Yield Clinical Pearls for NEET-PG:** * **Demographics:** Most common in **Asian males**, despite hyperthyroidism being more common in females. * **Triggers:** High-carb meals, alcohol, and rest after heavy exercise. * **Management:** Propranolol (non-selective beta-blocker) is the treatment of choice as it reverses the overactivity of the Na+/K+ pump [1]. * **Caution:** Be careful with aggressive K+ replacement; as the episode resolves, potassium shifts back out of cells, leading to a risk of **rebound hyperkalemia**.

Q: A 19-year-old man presents with early fatigue and muscle cramps during sports. He is asymptomatic during walking or less intense activities. Physical examination and vital signs are normal. Muscle bulk, tone, and strength in proximal muscles are normal, with no fatigue during repetitive arm grip exercises. Following an exercise stress test, his serum creatine kinase (CK) is elevated, and lactate level is normal. Which of the following is the most likely diagnosis?

McArdle disease (glycogen storage disease). The clinical presentation of exercise-induced fatigue, muscle cramps, and elevated creatine kinase (CK) with a **normal lactate response** is classic for **McArdle disease (Glycogen Storage Disease Type V)** [1]. **1. Why McArdle Disease is Correct:** McArdle disease is caused by a deficiency of **myophosphorylase**, the enzyme responsible for breaking down glycogen into glucose-1-phosphate in muscles. During high-intensity exercise, muscles rely on glycogenolysis for energy [2]. In its absence, patients experience "exercise intolerance" and cramps. A hallmark diagnostic finding is the **failure of blood lactate to rise** during an ischemic exercise test because the metabolic block prevents the conversion of glycogen to glucose, and subsequently to lactate [1]. The "second wind" phenomenon (improvement in symptoms after 10–15 minutes of exercise due to increased fatty acid delivery) is also characteristic. **2. Why Other Options are Incorrect:** * **Gaucher Disease:** A lysosomal storage disease (glucocerebrosidase deficiency) characterized by hepatosplenomegaly, bone pain (Erlenmeyer flask deformity), and cytopenias, not exercise-induced muscle cramps. * **Tay-Sachs Disease:** A neurodegenerative condition (hexosaminidase A deficiency) presenting in infancy with developmental regression, cherry-red spots on the macula, and seizures. * **Hemochromatosis:** An iron overload disorder leading to "bronze diabetes," cirrhosis, and cardiomyopathy. It does not typically present with acute exercise-induced muscle breakdown. **Clinical Pearls for NEET-PG:** * **Enzyme Defect:** Myophosphorylase (Muscle Phosphorylase) [1]. * **Biochemical Marker:** Flat lactate curve with a significant rise in ammonia during exercise. * **Key Symptom:** "Second Wind" phenomenon. * **Complication:** Risk of rhabdomyolysis and myoglobinuria (red-brown urine) after intense exertion.

Q: All of the following drugs alter calcium hemostasis except-

Indomethacin. Calcium homeostasis is a tightly regulated process involving bone resorption, renal excretion, and intestinal absorption [1]. The correct answer is **Indomethacin**, as it does not have a primary or clinically significant effect on systemic calcium levels. **1. Why Indomethacin is the Correct Answer:** Indomethacin is a non-steroidal anti-inflammatory drug (NSAID) that acts by inhibiting cyclooxygenase (COX) enzymes. **2. Analysis of Incorrect Options:** * **Fluoride:** It is a potent stimulator of osteoblasts. Chronic exposure (fluorosis) leads to increased bone density and can cause **hypocalcemia** as calcium is rapidly deposited into the newly formed bone matrix. * **Mithramycin (Plicamycin):** This is a cytotoxic antibiotic that inhibits osteoclast activity. It was historically used as a potent agent to lower serum calcium in cases of **hypercalcemia of malignancy**. * **Thiazides:** These diuretics increase distal renal tubular calcium reabsorption [1]. They are a well-known cause of **mild hypercalcemia** and are therapeutically used to reduce hypercalciuria in patients with recurrent calcium stones. **Clinical Pearls for NEET-PG:** * **Thiazides** cause **Hyper**calcemia, whereas **Loop diuretics** (Furosemide) cause **Hypo**calcemia ("Loops lose calcium"). * **Mithramycin** is rarely used today due to hepatotoxicity and thrombocytopenia, replaced by Bisphosphonates and Denosumab. * **Vitamin D toxicity, Sarcoidosis, and Lithium** are other high-yield causes of drug/disease-induced hypercalcemia.

Q: Syndrome of apparent mineralocorticoid excess is due to?

Lack of inactivation of cortisol to cortisone. Syndrome of Apparent Mineralocorticoid Excess (SAME) is a genetic or acquired condition characterized by hypertension, hypokalemia, and metabolic alkalosis, despite having low plasma renin and low aldosterone levels. 1. Why the correct answer is right: The mineralocorticoid receptor (MR) in the distal tubule has an equal affinity for both aldosterone and cortisol. Under normal physiological conditions, the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) converts active cortisol into inactive cortisone [1]. This ensures that only aldosterone can activate the MR. In SAME, there is a deficiency or inhibition of 11β-HSD2. Consequently, cortisol is not inactivated; it floods the MR, mimicking the effects of aldosterone (mineralocorticoid excess) despite aldosterone levels being suppressed. 2. Why other options are wrong: * A & B: In SAME, aldosterone levels are actually suppressed (low) due to the negative feedback loop caused by the cortisol-induced volume expansion and hypertension. * C: Increased cortisol production is characteristic of Cushing’s Syndrome. While severe Cushing’s can overwhelm the 11β-HSD2 enzyme, SAME specifically refers to the failure of the inactivation process rather than primary overproduction. 3. NEET-PG High-Yield Pearls: * Etiology: Autosomal recessive mutation in the HSD11B2 gene or acquired via Licorice ingestion (Glycyrrhetinic acid inhibits 11β-HSD2). * Biochemical Marker: An increased ratio of Urinary Cortisol to Urinary Cortisone (THF+αTHF/THE). * Treatment: Potassium-sparing diuretics (Spironolactone or Eplerenone) or low-dose glucocorticoids (to suppress ACTH and endogenous cortisol production). * Differential: Liddle’s Syndrome also presents with low renin/aldosterone but is due to a gain-of-function mutation in the ENaC channel.

Q: In thyrotoxicosis, which of the following is NOT controlled by beta-blockers?

Oxygen consumption. Explanation: In thyrotoxicosis, the clinical manifestations arise from two distinct mechanisms: **increased sympathetic (adrenergic) activity** and a **hypermetabolic state** caused by direct action of thyroid hormones ($T_3$ and $T_4$) on tissues. **1. Why Oxygen Consumption is the Correct Answer:** Beta-blockers (like Propranolol) act by antagonizing $\beta$-adrenergic receptors. While they effectively mitigate the symptoms of sympathetic overactivity, they have **no effect on the basal metabolic rate (BMR)** or the direct calorigenic effects of thyroid hormones [2,3]. Increased oxygen consumption is a result of thyroid hormone-induced stimulation of $Na^+/K^+$ ATPase activity and mitochondrial respiration [4]. Since this is a direct metabolic effect and not mediated by catecholamines, beta-blockers cannot control it. **2. Why the other options are incorrect:** * **Anxiety and Tremors:** These are neurological manifestations of increased $\beta$-adrenergic sensitivity [3]. Beta-blockers cross the blood-brain barrier (especially Propranolol) and block peripheral receptors to effectively reduce these symptoms [1]. * **Tachycardia:** This is driven by increased $\beta_1$ receptor expression in the myocardium [4]. Beta-blockers are the first-line treatment to rapidly control heart rate in thyrotoxic patients [1]. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Propranolol is preferred in thyrotoxic crisis (thyroid storm) because, in high doses, it also inhibits the **peripheral conversion of $T_4$ to $T_3$** (by inhibiting 5'-deiodinase). * **Contraindication:** Avoid beta-blockers in patients with thyrotoxicosis who have co-existing **asthma**; use cardioselective agents (e.g., Atenolol) or Calcium Channel Blockers (Diltiazem) instead. * **Key Concept:** Beta-blockers provide **symptomatic relief** but do not treat the underlying hyperthyroidism [1].

Q: Which of the following is true about primary aldosteronism?

Increased sodium reabsorption. Primary Aldosteronism (Conn’s Syndrome) is characterized by the autonomous overproduction of aldosterone from the adrenal cortex, independent of the renin-angiotensin system. ### Explanation of Options * Correct Answer: C (Increased sodium reabsorption) Aldosterone acts on the principal cells of the distal convoluted tubule and collecting duct. It increases the expression of apical epithelial sodium channels (ENaC) and the basolateral Na+/K+ ATPase pump [1]. This leads to increased sodium reabsorption and water retention, resulting in hypertension. * Incorrect: A (Pedal edema) Despite significant sodium and water retention, patients with primary aldosteronism rarely present with edema. This is due to the "Aldosterone Escape" phenomenon: the initial volume expansion triggers the release of Atrial Natriuretic Peptide (ANP), which promotes pressure natriuresis, preventing overt fluid overload and edema [1, 2]. * Incorrect: B (Increased renin) In primary aldosteronism, the high levels of aldosterone cause volume expansion and hypertension, which provide negative feedback to the juxtaglomerular apparatus [2]. This results in suppressed (low) plasma renin activity. A high Aldosterone-to-Renin Ratio (ARR) is the classic screening tool. ### High-Yield Clinical Pearls for NEET-PG * Classic Triad: Hypertension, Hypokalemia, and Metabolic Alkalosis [1]. * Screening Test: Plasma Aldosterone Concentration (PAC) to Plasma Renin Activity (PRA) ratio > 20-30. * Confirmatory Test: Saline infusion test (failure to suppress aldosterone) or Oral salt loading test. * Most Common Cause: Adrenal Adenoma (Conn’s Syndrome), followed by Bilateral Adrenal Hyperplasia. * Treatment: Surgical resection for unilateral adenoma; Spironolactone (Aldosterone antagonist) for bilateral hyperplasia.

Question 1

Thyrotoxic periodic paralysis leads to extreme muscle weakness due to?

Accepted Answer

Hypokalemia

Answer

Hypocalcemia

Answer

Hypomagnesemia

Answer

Hyponatremia

Question 2

A 19-year-old man presents with early fatigue and muscle cramps during sports. He is asymptomatic during walking or less intense activities. Physical examination and vital signs are normal. Muscle bulk, tone, and strength in proximal muscles are normal, with no fatigue during repetitive arm grip exercises. Following an exercise stress test, his serum creatine kinase (CK) is elevated, and lactate level is normal. Which of the following is the most likely diagnosis?

Accepted Answer

McArdle disease (glycogen storage disease)

Answer

Gaucher disease

Answer

Tay-Sachs disease

Answer

Hemochromatosis

Question 3

A 52-year-old alcoholic presents with a skin rash on his chest, diarrhea, and abdominal pain. Examination reveals a scaly and pigmented rash on sun-exposed areas, a soft abdomen, and impaired short-term memory. The patient exhibits dermatitis, diarrhea, and dementia syndrome. What is the most likely diagnosis for this patient's vitamin deficiency or excess?

Accepted Answer

niacin

Answer

thiamine

Answer

pyridoxine

Answer

vitamin C

Question 4

All of the following drugs alter calcium hemostasis except-

Accepted Answer

Indomethacin

Answer

Fluoride

Answer

Mithramycin

Answer

Thiazides

Question 5

Hypoglycemia is a recognized feature of all of the following conditions, except?

Accepted Answer

Acromegaly

Answer

Uremia

Answer

Addison's disease

Answer

Hepatocellular failure

Question 6

Tumor-induced hypoglycemia is seen in all of the following EXCEPT:

Accepted Answer

Lymphoma

Answer

Mesenchymal tumors

Answer

Hepatocellular carcinoma

Answer

Adrenal carcinoma

Question 7

Syndrome of apparent mineralocorticoid excess is due to?

Accepted Answer

Lack of inactivation of cortisol to cortisone

Answer

Increased aldosterone production

Answer

Lack of inactivation of aldosterone

Answer

Increased cortisol production

Question 8

In thyrotoxicosis, which of the following is NOT controlled by beta-blockers?

Accepted Answer

Oxygen consumption

Answer

Anxiety

Answer

Tremors

Answer

Tachycardia

Question 9

Which of the following is true about primary aldosteronism?

Accepted Answer

Increased sodium reabsorption

Answer

Pedal edema

Answer

Increased renin

Answer

All of the above

Question 10

A patient with pheochromocytoma would secrete which of the following in a higher concentration?

Accepted Answer

Norepinephrine

Answer

Epinephrine

Answer

Dopamine

Answer

VMA

Endocrinology — MCQs

Endocrinology — MCQs

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