Polymyositis with hypokalemia: correction with potassium replacement in the absence of steroids

A patient presented with typical polymyositis, but also with hypokalemia. Correction of potassium deficit without corticosteroids led to complete resolution of symptoms and laboratory abnormalities. Muscle biopsy performed after correction of the hypokalemia revealed focal fiber necrosis with regeneration and inflammatory infiltrate that contained, among others, many eosinophils. Hypokalemia should be considered in the differential diagnosis of polymyositis even in the face of an inflammatory muscle infiltrate.