Q. Which hormone is elevated in Addison’s disease, leading to hyperpigmentation?

Correct Answer: B. ACTH

In Addison's disease (primary adrenal insufficiency), the adrenal cortex fails to produce adequate cortisol and aldosterone. This loss of negative feedback on the anterior pituitary leads to unopposed elevation of ACTH (adrenocorticotropic hormone). ACTH is a 39-amino acid peptide derived from the precursor molecule POMC (pro-opiomelanocortin), which also generates melanocyte-stimulating hormone (MSH). Both ACTH and MSH are potent melanogenic peptides that bind to melanocortin-1 receptors on melanocytes, stimulating melanin synthesis and deposition in the skin and mucous membranes. This results in the characteristic bronze or dark hyperpigmentation seen in Addison's disease—particularly in sun-exposed areas, skin creases, and the oral mucosa. The degree of pigmentation correlates with ACTH levels. In Indian clinical practice, Addison's disease is less common than in developed nations but remains an important differential in patients presenting with hyperpigmentation, hyponatremia, and hypotension. The hyperpigmentation is a clinical hallmark that distinguishes primary adrenal insufficiency from secondary adrenal insufficiency (where ACTH is low and pigmentation is absent). Measurement of elevated ACTH with low cortisol confirms the diagnosis.

Why the other options are wrong

A. Aldosterone — Aldosterone is decreased in Addison's disease due to adrenal cortical destruction, not elevated. While aldosterone deficiency contributes to hyponatremia and hyperkalemia, it has no role in melanin synthesis. Aldosterone acts on the collecting duct to regulate sodium and potassium, not pigmentation. This is a common trap—students confuse adrenal hormone deficiencies with the secondary compensatory rise in ACTH. C. Renin — Renin is elevated in Addison's disease due to hypovolemia and sodium depletion, but it is a renal enzyme, not a pituitary hormone. Renin activates the renin-angiotensin-aldosterone system (RAAS) to conserve sodium, not to stimulate melanin production. Renin has no melanogenic activity and does not bind melanocortin receptors. This option confuses the RAAS response with the pituitary-adrenal axis. D. Cortisol — Cortisol is markedly decreased in Addison's disease—this is the defining biochemical abnormality. Low cortisol is what triggers the compensatory rise in ACTH via loss of negative feedback. Cortisol itself has no melanogenic properties and does not cause hyperpigmentation. Confusing low cortisol with the secondary ACTH elevation is a classic NBE trap designed to test understanding of the feedback axis.

High-Yield Facts

Mnemonics

PAC-ACTH in Addison's Primary adrenal insufficiency → AACTH Crises (unopposed feedback loss). Secondary adrenal insufficiency → ACTH falls. Use this to distinguish primary from secondary Addison's. POMC → Pigmentation POMC (pro-opiomelanocortin) is cleaved to produce both ACTH and MSH (melanocyte-stimulating hormone). Both drive melanin synthesis → bronze skin in Addison's.

NBE Trap

NBE pairs "Addison's disease" with "hyperpigmentation" to lure students into choosing aldosterone or renin (which are also abnormal in Addison's) instead of recognizing that only ACTH/MSH have melanogenic activity. The trap tests whether students understand the POMC-derived melanogenic pathway versus general adrenal hormone dysfunction.

Clinical Pearl

In Indian clinical practice, a patient presenting with hyperpigmentation, fatigue, and hyponatremia should raise suspicion for Addison's disease. The bronze discoloration of the oral mucosa and palmar creases is a bedside clue that distinguishes primary adrenal insufficiency from other causes of hyperpigmentation (e.g., hemochromatosis, Minamata disease). Checking ACTH and cortisol levels at 8 AM (when cortisol is highest) followed by a short synacthen test confirms the diagnosis.

_Reference: Harrison Ch. 375 (Adrenal Insufficiency); Robbins Ch. 24 (Endocrine Pathology); KD Tripathi Ch. 31 (Adrenocorticotropic Hormone)_