Anti-synthetase syndrome is an autoimmune disease characterized by autoantibodies toward amino acyl-tRNA synthetases (ARS), anti-Jo 1 being the most commonly detected. Muscle damage develops in up to 90% of ARS-positive patients, characterized by a necrotizing myositis restricted to the perifascicular region. This topographic distribution of muscle damage may lead to a misdiagnosis of DM at muscle biopsy. Despite similar clinical and morphological presentation, DM and ASS have a different prognosis, for instance, patients with ASS are prone to develop more aggressive complications requiring multi-modality immunosuppressive therapy. Aim of the present study will be to compare morphological, immunohistochemical and histoenzymatic features of muscle from ASS patients with those of DM ones. In addition, since a vasculopathy characterized by C5b9 deposition has been demonstrated both in DM and ARS-associated myositis, we will investigate capillary density both in the peripheral and central portion of the muscle fascicle. Finally, we will evaluate markers of mitochondrial damage to provide a further distinction between the two diseases.
Anti-synthetase syndrome is an autoimmune disease characterized by the presence of autoantibodies toward amino acyl-tRNA synthetases, anti-Jo 1 being the most commonly detected (up to 85%). Clinical manifestations include: myositis, ILD, arthritis, Raynaud¿s phenomenon, "mechanic's hand" and fever. These features may emerge at different time-points during follow-up making difficult to reach a diagnosis, especially in Jo 1 negative patients. In fact, although commercial kits are available for routine ARS-antibodies screening, tests for anti aminoacyl-tRNA synthetase other than anti-Jo 1, may be not accessible to all hospitals. Moreover, commercial tests may lack specificity. In this setting muscle biopsy still represents a valuable tool in a multidisciplinary approach to make a correct diagnosis.
The present study will provide histological, histochemical and immunohistochemical clues for the differential diagnosis of ARS-related myositis and DM on muscle biopsy. These two entities share the perifascicular pattern of muscle damage distribution and may show a similar clinical presentation, explaining the reason why most ARS-positive patients had been previously classified as DM (up to 77% in two large series of patients).