Non-necrotizing autoimmune myopathy with pipestem type capillaries - a light and electron microscopic study

We report on 7 cases of a nonnecrotizing type of autoimmune myopathy found in suspected connective tissue disease and related disorders. In muscle biopsy, these cases showed myopathic alterations characterized by irregular outlines of muscle fibers in cross and longitudinal section nearly or totally lacking inflammatory cell infiltrations or macrophages and no necroses of myofibers. They revealed deposition of immunoglobulins and of collagen IV antibodies attached to fiber surface. The number of capillaries per myofiber was enlarged. Capillaries of pipestem type with thickened wall were found at the electron microscopic level. This type of myopathy was seen especially in subacute cases presenting with muscle pain, weakness and increased unspecific inflammatory laboratory parameters. No evidence for polymyositis, dermatomyositis or inclusion body myositis could be found. In all cases, steroid therapy was of striking benefit.