Ultrastructural changes of skeletal muscles in polyarteritis nodosa and in arteritis assoicated with rheumatoid arthritis.

Muscle biopsies from two cases of polyarteritis nodosa (PN) and one of arteritis in assoication with rheumatoid arthritis (RA) were examined by electron microscopy. The histological changes were similar in all three cases. The endothelial cells of the small blood vessels were often hypertrophied. Inflammatory reaction was present mainly in the vicinity of the blood vessels. Individual muscle fibres showed mostly nonspecific degenerative changes. In a case PN, however, annulate lamellae were present in a small number of the muscle fibres. The annulate lamellae have been reported, to our knowledge, in the human skeletal muscles only in a few cases of polymyositis. In addition, two cases, one of PN and of arteritis with RA, showed fine filamentous inclusions in the muscle fibres. Changes were also noted in the motor end-plate. A sural nerve biopsy in a case of arteritis with RA showed changes both in axons and myelin sheaths, in addition to the changes in the blood vessels similar to those in the muscle.