Inclusion body myositis.

The histochemical and ultrastructural study of muscle biopsies of two patients with a chronic muscle weakness and wasting showed particular changes in muscle fibers: (1) peripheral lined vacuoles, containing whorls of membranes and cytoplasmic debris; (2) collections of intranuclear and intrasarcoplasmic tubular filaments (16-18 nm in external diameter and 6.5 nm in inner diameter). These changes are characteristic of a rare muscle disorder termed inclusion body myositis; its individuality is favoured by the present study. The resemblance of the tubular filaments to myxovirus nucleocapsid has been suggested by various authors but attempts to isolate the virus were unsuccessful in several reported cases as well as in those here presented. This does not exclude a viral origin of the disease. The similarity of the tubular filaments to thick myofilaments has been invoked by others, but has not been demonstrated. At the present the nature of the abnormal filaments remains unknown.