Autoantibodies against melanoma differentiation-associated protein 5 (MDA5) have been described in several Asian dermatomyositis (DM) cohorts, often associated with amyopathic DM and rapidly progressive interstitial lung disease (ILD). A recent study of a DM cohort seen at a US dermatology clinic reports that MDA5 autoantibodies are associated with a unique cutaneous phenotype. Given the widening spectrum of clinical findings, we evaluated the clinical features of anti-MDA5-positive patients seen at a US myositis referral center.
160 DM patients were screened for MDA5 autoantibodies by immunoprecipitation and antibody titers were analyzed in longitudinal serum samples. Anti-MDA5 positive patients were evaluated for the presence of additional myositis autoantibodies. Patient clinical characteristics were compared by retrospective chart review.
MDA5 was targeted in 11/160 (6.9%) patients with DM. Of these, nine presented with a symmetric polyarthropathy, six demonstrated overt clinical myopathy and eight had ILD. Eight anti-MDA5-positive patients exhibited the clinical attributes of the antisynthetase syndrome in the absence of Jo-1 or other anti-synthetase autoantibodies. MDA5 autoantibody titers did not correlate with clinical course.
MDA5 autoantibodies are found in DM patients presenting with a symmetric polyarthritis, clinically similar to rheumatoid arthritis. These patients often have features of the antisynthetase syndrome, but in the absence of antisynthetase autoantibodies. Most anti-MDA5 positive patients had overt clinical myopathy and ILD. The latter, while occasionally severe, typically resolved with immunosuppressive therapy. In this cohort, the MDA5 phenotype is frequently a clinical mimic of the antisynthetase syndrome and is not associated with rapidly progressive ILD.