Clinical Images: Anti‐ <scp>MDA5</scp> dermatomyositis with rapidly progressive interstitial lung disease presenting with rapidly progressive glomerulonephritis due to <scp>C3</scp> glomerulopathy

The patient, a 64-year-old woman with hypertension and type II diabetes, was admitted to the hospital for acute kidney injury with nephrotic range proteinuria. Before admission, she had three months of duskiness of the distal fingertips with mottling, or livedo reticularis. Computed tomography of the chest demonstrated increasing upper-lobe peribronchovascular consolidations and ground glass opacities with an organizing pneumonia pattern. Renal biopsy demonstrated glomerulonephritis with focal immune deposits that stained exclusively for C3 (A and B), consistent with rapidly progressive glomerulonephritis (RPGN) due to C3 glomerulopathy. Given her skin changes and worsening hypoxemia concerning for rapidly progressive interstitial lung disease (RP-ILD), myositis-specific antibody testing was obtained and demonstrated anti-MDA5 antibody positivity (74 units; reference interval <20 units), confirming anti-MDA5 dermatomyositis (DM). She had normal muscle strength and a normal creatine kinase level, consistent with an amyopathic presentation. Her ferritin level, a prognostic marker of anti-MDA5 DM RP-ILD,1 increased from 1,232 to 5,260 ng/mL, corresponding with acutely worsening hypoxemia requiring intubation. She was initially treated with mycophenolate mofetil, high-dose steroids, and rituximab and required escalation to cyclophosphamide, tacrolimus, and intravenous Ig due to worsening oxygen requirements. She ultimately died of pulmonary and renal failure. Renal involvement in idiopathic inflammatory myopathies is extremely rare, although it has been described2; however, anti-MDA5 DM is not known to present with renal disease. Although a single case report has described anti-MDA5 DM presenting with thrombotic microangiopathy,3 this is the first case describing anti-MDA5 DM and RPGN secondary to C3 glomerulopathy, highlighting the importance of recognizing renal involvement as a rare but possible overlap with anti-MDA5 DM. Verbal consent was obtained from the patient and the patient's family before case write up. Disclosure form. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.