Development of anti-MDA5 autoantibody-positive dermatomyositis following the use of etanercept biosimilar in rheumatoid arthritis.

The induction of autoimmune diseases during tumour necrosis factor-alpha inhibitor (TNFi) usage has been described. Herein, we report a rare case of a 49-year-old woman with antimelanoma differentiation-associated gene 5 (MDA5) antibody (Ab)-positive dermatomyositis (DM), which developed 5 weeks after the introduction of an etanercept biosimilar to rheumatoid arthritis (RA). Four of the five known cases, including ours, of anti-MDA5Ab-positive DM complicated with RA revealed anti-MDA5Ab-positive DM following TNFi usage. When patients with RA are diagnosed with interstitial lung disease during TNFi usage, anti-MDA5 Ab-positive DM could be a differential diagnosis.