Immunoglobulin deposition in skeletal muscle in primary muscle diseases

Using direct immunofluorescence the deposition of IgG, IgM, IgA, Clq and C3 was studied on muscle biopsies from 39 patients with polymyositis/dermatomyositis, 21 patients with muscular dystrophy, 57 other disease controls and 10 healthy volunteers. Three staining patterns were observed, sarcolemma/basement membrane blood vessel wall and intrafibrous. Sarcolemma/basement membrane staining, but not blood vessel wall or intrafibrous staining, occurred more frequently (p less than 0.05) in the polymyositis/dermatomyositis group compared with the two other disease groups. Immunoglobulin deposition was useful in distinguishing myopathic from neuropathic disorders. Grouping the patients into those with connective tissue diseases and those without, sarcolemma/basement membrane and blood vessel wall staining were shown to distinguish the two groups (p less than 0.05). An analysis of the histological abnormalities in the polymyositis/dermatomyositis group was performed and related to immunoglobulin/complement deposition. Fibre damage, rather than the presence of a mononuclear perivascular infiltrate, was shown to be the best correlate with each of the three staining patterns. Immunoglobulin and/or complement deposition in skeletal muscle is an abnormal finding and the results described support the notion that humoral abnormalities may be detected frequently in polymyositis/dermatomyositis. In addition, the inability to distinguish polymyositis/dermatomyositis from muscular dystrophy limits the potential value of direct immunofluorescence as a diagnostic tool.