The immunopathogenic role of complement in human muscle disease.

The complement system has been shown to play a pathogenic role in only a small number of muscle diseases. A complement-induced microangiopathy is important in dermatomyositis and in the rare disorder, necrotizing myopathy with pipestem capillaries. Recent studies demonstrate the reversibility of microvascular damage in dermatomyositis by intravenous immune globulin which appears to intercept the assembly and deposition of membrane attach complex. In myasthenia gravis, complement-mediated lysis directed at the acetylcholine receptor leads to a cascade of events reducing the number of receptors, simplifying the complex architecture of the junctional folds and decreasing the available surface for the insertion of new receptors. The newest condition in which a role for complement has been demonstrated is X-linked vacuolated myopathy. The condition is of interest because membrane attack complex deposits result in shedding of complement-laden membrane fragments in contrast to a cytolytic process as the consequence of assembly of the terminal complement components.