A patient presents with fatigue, muscle cramps, and strong salt cravings. What is the most likely diagnosis?

Correct Answer: C. Addison’s disease

Addison's disease (primary adrenal insufficiency) presents with the classic triad of fatigue, muscle cramps, and salt cravings due to combined cortisol and aldosterone deficiency. The fatigue results from loss of cortisol's permissive effects on catecholamine action and metabolic homeostasis. Muscle cramps arise from hyponatremia and hypokalemia secondary to aldosterone loss, which impairs renal sodium reabsorption and potassium excretion. The intense salt cravings are a compensatory mechanism—patients instinctively seek sodium to counteract ongoing urinary losses. In India, tuberculosis remains the leading cause of Addison's disease (accounting for ~70% of cases), followed by autoimmune destruction. The diagnosis is confirmed by low morning cortisol (<3 µg/dL) with elevated ACTH (>100 mIU/L), and the short synacthen test shows inadequate cortisol response. Hyperpigmentation (due to ACTH-driven melanin production) is often the clinical clue that distinguishes primary from secondary adrenal insufficiency. Treatment with glucocorticoid and mineralocorticoid replacement (hydrocortisone + fludrocortisone) rapidly reverses symptoms.

Why the other options are wrong

A. Hypopituitarism — Hypopituitarism causes secondary adrenal insufficiency with low cortisol but low ACTH (not elevated). While fatigue occurs, salt cravings are absent because aldosterone production is relatively preserved (the renin–angiotensin system remains intact). Hyponatremia is less severe. This is the NBE trap—students may confuse 'adrenal insufficiency' symptoms without distinguishing primary from secondary. B. Cushing's disease — Cushing's disease presents with hypertension, weight gain, proximal muscle weakness (not cramps), and hypokalemia—but patients have salt retention, not cravings. Cortisol is elevated, not deficient. The clinical picture is opposite: excess glucocorticoid and mineralocorticoid effects. This option tests whether students confuse adrenal excess with deficiency. D. Conn's disease — Conn's syndrome (primary hyperaldosteronism) causes hypertension and hypokalemia but not fatigue or salt cravings. Patients have sodium retention and hypertension, not sodium loss. Cortisol levels are normal. The NBE trap here is pairing 'salt' with aldosterone disorders—but only Addison's (with aldosterone loss) triggers compensatory salt-seeking behavior.

High-Yield Facts

Mnemonics

ADDISON'S CLASSIC TRIAD Adrenal insufficiency → Fatigue, Salt cravings, Muscle cramps. Remember: loss of both cortisol (energy) and aldosterone (sodium retention) = fatigue + salt-seeking + electrolyte cramps. PRIMARY vs SECONDARY Adrenal Insufficiency PRIMARY (Addison's): Low cortisol + HIGH ACTH + hyperpigmentation. SECONDARY (Hypopituitarism): Low cortisol + LOW ACTH + no pigmentation. Mnemonic: 'Primary = Pigment' (ACTH-driven melanin).

NBE Trap

NBE pairs 'salt cravings' with aldosterone disorders to lure students toward Conn's disease. However, Conn's causes salt retention and hypertension, not cravings. Only Addison's (aldosterone loss) triggers compensatory salt-seeking. The trap tests whether students understand the direction of electrolyte abnormality, not just the hormone name.

Clinical Pearl

In Indian clinical practice, always screen TB patients on anti-TB therapy for adrenal insufficiency—TB-induced Addison's can present insidiously with fatigue mistaken for TB toxicity. A patient with persistent fatigue despite good TB adherence and rising ACTH should trigger suspicion. Stress-dose steroids during acute illness (surgery, infection) are life-saving in undiagnosed Addison's.

_Reference: Harrison Ch. 375 (Adrenal Insufficiency); KD Tripathi Ch. 56 (Adrenocorticotropic Hormone & Adrenal Steroids)_