Antisynthetase syndrome.

Autoantibodies to eight of the aminoacyl-transfer RNA synthetases-the most well-recognized of which is anti-histidyl (Jo-1)-have all been implicated in the pathogenesis of antisynthetase syndrome (AS). AS is characterized by varying degrees of interstitial lung disease, myositis, arthropathy, fever, Raynaud's phenomenon, and mechanic's hands, and the morbidity and mortality of the disease are usually linked to the pulmonary findings. The value of a lung biopsy in AS cannot be overemphasized, as it serves to describe the underlying etiology of the interstitial lung disease, guide therapy, and estimate prognosis. Muscle disease shares many clinical features of polymyositis, yet histologically, the inflammatory involvement resembles that of dermatomyositis. Because inflammatory arthritis mimics rheumatoid arthritis, AS should be considered in atypical cases. Corticosteroids are the mainstay of acute therapy, although treatment often requires immunosuppressant medications such as cyclophosphamide, azathioprine, mycophenolate mofetil, cyclosporine, tacrolimus, or rituximab.