Conn's syndrome (primary hyperaldosteronism) simulating polymyositis.

A 44-year-old woman presented with typical polymyositis findings associated with hypokalemia. Abdominal CT as well as plasma renin and aldosterone levels showed a right surrenal adenoma secreting aldosterone. Unilateral adrenalectomy was performed and resolved all the clinical and laboratory manifestations. Hypokalemia should be considered in the differential diagnosis of polymyositis, even in the face of inflammatory cell infiltration in the muscle biopsy.