A hallmark finding in primary adrenal insufficiency (Addison disease) is?

• A. Hyperkalemia with hypernatremia.
• B. Hyperpigmentation with hypertension.
• C. Hyperpigmentation with hyponatremia.
• D. Hypercalcemia with polyuria.

Answer: (C)

In primary adrenal insufficiency, destruction of the adrenal cortex lowers both cortisol and aldosterone. The lack of aldosterone leads to salt wasting, so sodium levels fall (hyponatremia) and potassium can rise, with volume depletion and low blood pressure. At the same time, ACTH rises to try to stimulate the adrenals, and because ACTH shares a precursor with melanocyte-stimulating hormone, the skin becomes hyperpigmented. This combination of darkening of the skin and low sodium is a classic clue to Addison disease.

The other pairings don’t fit the typical pattern. Hyperkalemia with hypernatremia would not occur because the body loses sodium with aldosterone deficiency, not retains it; hypertension is not expected in Addison disease, which usually causes hypotension; hypercalcemia with polyuria isn’t characteristic of primary adrenal failure.