Myopathy with anti-Jo-1 antibodies: pathology in perimysium and neighbouring muscle fibres.

OBJECTIVE To evaluate muscle pathology and clinical characteristics in patients with a myopathy and serum antibodies to the Jo-1 antigen (histidyl t-RNA synthetase). BACKGROUND Anti-Jo-1 antibodies occur in syndromes that may include muscle weakness and pain, Raynaud's phenomenon, interstitial lung disease, arthritis, and a skin rash different from that seen in dermatomyositis. The muscle pathology is not well defined. METHODS Case series. Review of charts, muscle biopsies, and laboratory records. Features of myopathology in 11 patients with anti-Jo-1 antibody associated myopathies were compared with other types of inflammatory myopathies. RESULTS Myopathology in patients with anti-Jo-1 antibodies consistently included fragmentation of, and macrophage predominant inflammation in, perimysial connective tissue. Perifascicular myopathic changes, including atrophy, regenerating muscle fibres, and some muscle fibre necrosis, were most common in regions near the connective tissue pathology and were most prominent in patients with more severe weakness. Unlike many other inflammatory myopathies, inflammation in endomysial and perivascular regions was uncommon. By contrast with dermatomyositis, capillary density was normal. CONCLUSIONS Myopathological changes in the anti-Jo-1 antibody syndrome include perimysial connective tissue fragmentation and inflammation, with muscle fibre pathology in neighbouring perifascicular regions. Myositis with anti-Jo-1 antibodies may result from an immune mediated disorder of connective tissue.