Autoantibody to transcriptional intermediary factor-1β as myositis-specific antibody: clinical correlation with CADM or DM with mild myopathy.

Background Myositis-specific autoantibodies (MSAs) are associated with unique clinical subsets in polymyositis/dermatomyositis (PM/DM). Autoantibodies against transcriptional intermediary factor (TIF)-1 gamma and TIF-1 alpha are known to be MSAs. Previously, we reported that TIF-1 beta is also targeted in patients with DM with or without concomitant anti-TIF-1 alpha/gamma antibodies. Objectives To evaluate the clinical features of seven cases with anti-TIF-1 beta antibodies alone. Methods Serum autoantibody profiles were determined, and protein and RNA immunoprecipitation studies were conducted. Western blotting was performed to confirm autoantibody reactivity against TIF-1 beta. Results Anti-TIF-1 beta antibody was identified by immunoprecipitation assay in 24 cases. Among them, seven patients were positive for anti-TIF-1 beta antibody alone. Six of the seven patients were classified as having DM. Among the six cases of DM, two patients had no muscle weakness and normal creatine kinase (CK) levels, and were classified as having clinically amyopathic DM. Four patients had muscle weakness, but three of them had normal serum CK levels that responded well to systemic steroids. Characteristic features of DM included skin rashes, such as Gottron sign, periungual erythema, punctate haemorrhage on the perionychium and facial erythema including heliotrope, which were observed in 86%, 57%, 86% and 71% of our cases, respectively. One of the seven patients had appendiceal cancer. None of the patients had interstitial lung disease. Conclusions Seven patients were confirmed to have anti-TIF-1 beta antibody without any other MSAs, including TIF-1 alpha/gamma antibodies, and six of them were diagnosed with DM. We suggest that anti-TIF-1 beta antibody is an MSA, and that it is associated with clinically amyopathic DM or DM with mild myopathy.