Case Report: Eosinophilic fasciitis with PM-Scl antibody positivity: expanding the serological spectrum

Eosinophilic fasciitis (EF) is a rare connective tissue disorder characterized by symmetrical or asymmetrical skin induration, fascial inflammation, and peripheral eosinophilia. We report the case of a middle-aged man presenting with left knee pain and swelling, progressive skin induration and pigmentation changes on the thigh and trunk. Blood workup showed peripheral eosinophilia and weakly positive PM-Scl-100 antibodies. MRI demonstrated fascial thickening with subcutaneous edema and fluid tracking along fascial planes, as well as a moderate knee effusion. Muscle biopsy confirmed eosinophilic fasciitis without muscle involvement. He was treated with high-dose prednisolone, methotrexate as a steroid-sparing agent, and adjunctive bone and infection prophylaxis, with marked clinical improvement at follow-up. This case highlights the diagnostic challenges in atypical presentation of eosinophilic fasciitis in the presence of overlap autoantibodies. Careful clinicopathological correlation is critical to exclude other differentials as EF can mimic systemic sclerosis or myositis. Biopsy can improve diagnostic certainty particularly when encountering auto-antibodies that have some association with other diagnoses.