Hypomyopathic Dermatomyositis Presenting with Idiopathic CD4 T-lymphocytopenia and Delayed Anti-MDA5 Positivity

A 47-year-old Haitian male with no known past medical history was admitted to the hospital for gradually progressive dyspnea, nonproductive cough, and weight loss. He also endorsed a one-year history of joint pains. He was febrile and tachycardic and in mild respiratory distress. Other pertinent physical examination findings included diffuse inspiratory crackles, digital ulcers, and symmetric swelling of the wrists, elbows, shoulders, and knees. He was found to have a right basilar consolidation on chest computed tomography (CT) and was placed on antibiotics for presumptive pneumonia. His CD4 count was 158 cells per microliter despite testing negative for human immunodeficiency virus (HIV). A thorough infectious workup was unrevealing, and he did not improve with antibiotics. He had a weakly positive anti-nuclear antibody (ANA) with an otherwise negative rheumatologic workup. Creatinine kinase and aspartate aminotransferase were mildly elevated in the absence of overt muscle weakness. A myositis panel, including melanoma differentiation-associated protein five (anti-MDA5) antibody, was negative at the time. He was discharged on a short course of prednisone without a definitive diagnosis. He returned several months later with worsening respiratory symptoms. At this time, a lung biopsy revealed interstitial lung disease. Repeat myositis panel demonstrated anti-MDA5 positivity. The patient was also found to have new-onset non-ischemic heart failure with reduced ejection fraction. A diagnosis of hypomyopathic dermatomyositis was made based on clinical, laboratory, and imaging findings. The patient was restarted on prednisone, and mycophenolate mofetil was subsequently initiated for maintenance therapy.