Glomerulonephritis associated with polymyositis

Five patients with primary idiopathic polymyositis developed proteinuria associated with urine sediment abnormalities. Renal biopsies disclosed a focal mesangial proliferative glomerulonephritis with deposits of immunoglobulin and complement. After treatment of the polymyositis with corticosteroids, proteinuria and urine sediment changes disappeared within 4 to 8 wk along with an improvement in the muscle disease. Although the pathogenesis remains to be determined, immune complexes may be implicated in the etiology of this renal lesion.