Addison's disease masked by long-term exogenous steroid treatment for presumed polymyalgia rheumatica.

Addison's disease can present insidiously. A 78-year-old woman presented with non-specific symptoms and hyponatremia, with a previous history of polymyalgia rheumatica treated with glucocorticoids. Subsequent investigations were consistent with primary rather than secondary adrenal failure. Primary autoimmune Addison's disease can present with protean symptoms and diagnosis is often delayed. A high index of suspicion remains the cornerstone of diagnosis.