Histopathological features of rapidly progressive interstitial lung disease associated with anti-MDA5 dermatomyositis: a case series and literature review.

Dermatomyositis (DM) is a rare autoimmune inflammatory myopathy disorder that affects skeletal muscles, skin, and other organs including the lungs. DM is associated with anti-melanoma differentiation-associated gene 5 (MDA5) antibody and is frequently complicated by rapidly progressive interstitial lung disease (RPILD), leading to poor prognosis. Reports describing histopathological features in detail were limited in the literature. We retrospectively identified and reviewed the morphological features in the explanted lung specimens of six patients with RPILD associated with DM between 2016 and 2023. The mean age of our cohort was 47.5 years with a female predominance (67%). All cases showed diffuse alveolar damage (DAD) of varying phases and extent with some resembling a fibrotic non-specific interstitial pneumonia pattern in the background. In addition, we performed a literature review of RPILD associated with anti-MDA5 antibody-positive DM with depictions of histopathological features. Our findings suggest that acute lung injury characterised by varying phases of DAD are the hallmark of fulminant and/or treatment-refractory RPILD associated with DM, and we highlight issues in identifying this process on small biopsies.