The fine structure of polymyositis, with consideration of capillaries and subcellular organelles

Abstract

SUMMARYThickened skeletal muscle capillary basement membranes, sarcolemmal nuclear inclusions suggestive of viruses, and muscle fiber mitochondrial alterations have been reported by others in skeletal muscle biopsy specimens from patients with polymyositis. In this study, muscle biopsy specimens from three females exemplifying the main clinical syndromes of polymyositis—childhood dermatomyositis, adult dermatomyositis associated with neoplasia, and late-onset polymyositis—were examined with the electron microscope to further investigate these pathogenetic and etiological possibilities. All 34 capillaries (less than 6 μ in diameter) examined from the first two cases had basement membranes which fell within a highly variable range of normal (1,550 to 4,400 Ångströms) established by study of over 100 capillaries from five normal individuals. Six of thirteen capillaries from the third patient had definitely thickened basement membranes of 4,850 to 8,500 Ångströms, but there was concomitant diabetes mellitus. All skeletal muscle nuclei were free of morphological evidence of viral infection and were indistinguishable from controls, even in severely altered fibers. No definite abnormalities of mitochondria or other subcellular organelles were seen; the severe but nonspecific myofibrillar degeneration was as has been described by previous investigation. It is concluded that abnormalities of skeletal muscle capillaries and, specifically, their basement membranes have yet to be demonstrated in dermatomyositis or polymyositis uncomplicated by diabetes mellitus. The absence of sarcolemmal nuclear inclusions or noteworthy changes of other subcellular components (other than the myofibrils) indicates that such findings may not be present in every case, may occur only during limited phases of the disease, or are very sparsely distributed in the tissue.