C62-26 Resolution of Severe Pneumomediastinum With Aggressive Immunomodulation in a Child With Anti-MDA5-Positive Juvenile Dermatomyositis-Related Interstitial Lung Disease

Abstract Background Anti-MDA5-positive juvenile dermatomyositis (JDM) is a distinct clinical subtype of JDM with high risk of rapidly progressive interstitial lung disease (ILD). Despite aggressive immunosuppression, there is risk for spontaneous pneumomediastinum, a life-threatening alveolar rupture from inflammation and fibrosis, and mortality remains high. Case Report A 7-year-old girl was diagnosed with anti-MDA5-positive JDM due to consistent rash and muscle weakness. Initial therapy included intravenous immunoglobulin (IVIg), mycophenolate mofetil (MMF), and glucocorticoids (both oral and IV). She was treated with isoniazid due to an indeterminate tuberculosis (TB) test in the setting of long-term exposure to a TB-positive individual. Six-months after diagnosis, she presented to the ED with neck swelling and was found to have pneumomediastinum prompting hospital admission. Chest CT (Figure1A) demonstrated moderate pneumomediastinum tracking into the neck and shoulders with small bilateral pneumothoraxes, along with bilateral subpleural opacities suggestive of ILD. Rituximab was initiated with full CD20 depletion at second dose. She remained on room air. Serial CXRs showed persistent pneumomediastinum and similar pneumothoraxes, with concern for progressive lung fibrosis. She was transferred to our institution one month after her initial pneumomediastinum. On admission, the patient was comfortable on room air. Crepitus was palpable over the chest, neck, and face, with visible swelling of the neck and chest. Chest CT (Figure1B) showed peripheral reticular opacities, bronchial wall thickening, and traction bronchiectasis concerning for fibrosis, blebs, extensive pneumomediastinum, and small bilateral posterior pneumothoraxes. Labs were significant for high CXCL9 and IFN-1 score, suggesting active disease. Cyclophosphamide (CYC) was initiated, and MMF was discontinued. Six-minute walk test (6MWT) was normal without hypoxemia or dyspnea. WGS was unremarkable. She was discharged home on monthly IVIg, daily prednisolone, and CYC infusions with plans to continue rituximab and start tofacitinib (JAK inhibitor) once approved by insurance. Two months later, tofacitinib was initiated; cyclophosphamide was discontinued, and MMF was restarted, with gradual glucocorticoids tapering. She was clinically well at follow-up three months later, around three weeks after starting tofacitinib. Repeat chest CT (Figure1C) showed interval resolution of pneumothoraxes and pneumomediastinum with persistent but decreased subpleural opacities, reticulation, and traction bronchiectasis findings consistent with ILD/fibrosis. Notably, IL-18 levels and IFN-1 score had normalized. 6MWT had decreased pulse oximetry readings concerning for possible progressive ILD. Discussion This case describes a child with severe Anti-MDA5-positive JDM with ILD complicated by pneumomediastinum and evolving fibrosis who achieved air leak stabilization and decreased INF activity after aggressive immunosuppression including JAK inhibitor therapy. This abstract is funded by: none