Unusual renal involvement of polymyositis complicated with malignant hypertension

We report an autopsy case of polymyositis (PM) with unusual renal involvement representing malignant hypertension. The histopathological findings of the kidneys revealed marked onion-peel-like duplication of internal lamina and fibrous thickening of intima in the arteries. Arterioles showed hyalinous thickening of intima with marked luminal narrowing. In some glomeruli, fibrinoid necrosis of the capillary tuft were observed, and in these portions, afferent and efferent arterioles were also affected by the same changes. Immunohistochemical findings were the deposition of immunoglobulin M and complement C1q in the wall of vessels and the capillary tuft of glomeruli. Renin-secreting cells in the juxtaglomerular apparatus showed hyperplasia, corresponding with elevated serum renin and aldosterone activity. These histological and clinical findings were similar to those of scleroderma renal crisis. It is suggested that the immunological mechanism, mediated by immune complex and complement deposition, was responsible for the pathogenesis of this renal lesion.