1507 - Anti-MDA5 Antibody Mediated Myopathy: A Case Report

Case Diagnosis: Anti-MDA5 antibody associated myopathy

Case Description: A 52 year- old male with multiple comorbidities presented with progressive left leg and upper extremity weakness, recurrent falls, dysarthria, and right sided ptosis. Initial concern was for Guillain Barré syndrome, and IVIG was initiated with partial improvement. Evaluation revealed markedly elevated creatine kinase, severe hypothyroidism, and positive anti-MDA5 antibody. EMG demonstrated mixed polyneuropathy without decrement, and lumbar puncture was unrevealing. Muscle biopsy showed type II myofiber atrophy without signs of inflammatory myopathy. The patient was transitioned to a prednisone taper and entered inpatient rehabilitation, where he demonstrated functional gains. Outpatient follow-up revealed persistent mild proximal weakness and gait instability. Repeat myositis panel later showed negative anti-MDA5 with borderline anti-TIF-1γ positivity, suggesting contributions from both hypothyroid myopathy and possible inflammatory myopathy. Pulmonary and cardiac evaluations showed no evidence of interstitial lung disease or cardiomyopathy, common complications of MDA5-associated myositis.

Discussions: Anti-MDA5 antibody myopathy is rare but clinically important due to its association with rapidly progressive interstitial lung disease and cardiomyopathy. Anti-MDA5 ab is mostly typically associated with dermatomyositis. Diagnosis may be challenging in patients with overlapping neuromuscular and endocrine conditions. Hypothyroid myopathy can mimic inflammatory myopathies and confound serologic interpretation. Rehabilitation plays a vital role in maintaining independence during diagnostic uncertainty and treatment initiation.

Conclusions: This case illustrates the diagnostic complexity of progressive weakness with overlapping autoimmune, endocrine, and neuromuscular features. Recognition of anti-MDA5 antibody positivity should prompt interdisciplinary management and close surveillance for systemic complications, while rehabilitation ensures functional recovery amid ongoing diagnostic clarification.