Isolated Rapidly Progressive Interstitial Lung Disease Without Muscle or Skin Involvement in Idiopathic Inflammatory Myopathy: An Unusual Anti-Mi-2 Antibody Phenotype.

Anti-Mi-2 antibodies are myositis-specific autoantibodies typically associated with cutaneous manifestations in idiopathic inflammatory myositis with favourable outcomes. Interstitial lung disease (ILD), particularly rapidly progressive ILD (RP-ILD), is rarely linked to anti-Mi-2 and even more infrequently presents without muscle or skin involvement. We report a rare case of a 58-year-old male patient presenting with isolated RP-ILD without cutaneous or muscular manifestations. Laboratory evaluation revealed normal muscle enzymes and negative autoimmune markers, with myositis profile revealing isolated anti-Mi-2β antibody positivity, confirmed by enzyme-linked immunosorbent assay (ELISA) and immunoblot. Radiological features on high-resolution CT, coupled with the rapidity of progression, were suggestive of RP-ILD. Despite initial improvement with pulse corticosteroids and cyclophosphamide, the patient discontinued treatment and succumbed to the illness within two months. This case highlights an extremely rare anti-Mi-2 phenotype presenting solely with RP-ILD. Although anti-Mi-2 is typically linked to benign clinical courses, this case underscores its potential association with severe pulmonary manifestations in the absence of classic dermatomyositis features. Clinicians should be aware of atypical anti-Mi-2 presentations, including isolated RP-ILD. Early recognition and aggressive immunosuppressive therapy are critical to improving outcomes. Further research is essential to understand the underlying mechanisms and optimal management strategies in such presentations.