skip to main content

Addisonian Hyponatraemia — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

ModerateEndocrinologyAddisonian HyponatraemiaRACP Adult Medicine

A 45-year-old woman presents with hyponatraemia (Na⁺ 128 mmol/L), hypotension (BP 90/60), hyperkalaemia (K⁺ 5.8 mmol/L), and hyperpigmentation. She has nausea, fatigue, and weight loss. Morning cortisol is 85 nmol/L (very low). ACTH is 250 pmol/L (markedly elevated). What is the most likely cause?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Addison disease

Hyponatraemia with hyperkalaemia, hypotension, hyperpigmentation, very low cortisol, and markedly elevated ACTH is primary adrenal insufficiency (Addison disease). Aldosterone deficiency causes sodium loss (hyponatraemia) and potassium retention (hyperkalaemia). Cortisol deficiency causes impaired free water excretion (ADH is no longer suppressed by cortisol). Acute management: IV hydrocortisone 100 mg bolus then 50 mg q8h, IV normal saline. Lifelong replacement with hydrocortisone + fludrocortisone.

Reference: eTG Endocrine – 2024 – Adrenal Insufficiency; Endocrine Society 2016