Enterococcal pyomyositis in a rheumatoid arthritis patient under biologic therapy.

Pyomyositis is an uncommon bacterial infection of skeletal muscle, typically associated with tropical regions but increasingly reported in temperate climates among immunocompromised individuals. Staphylococcus aureus is the most frequently identified pathogen, whereas enterococcal pyomyositis is exceedingly rare. This report describes a case of Enterococcus faecalis pyomyositis in a patient with long-standing rheumatoid arthritis (RA) receiving combined immunosuppressive therapy. The 62-year-old woman with an 8‑year history of RA presented with a 2-month history of progressive right shoulder pain, swelling, fever, and chills. She had been treated with methotrexate, adalimumab, and low-dose corticosteroids. Laboratory evaluation revealed marked leukocytosis and significantly elevated inflammatory markers. Contrast-enhanced magnetic resonance imaging demonstrated a large multiloculated abscess involving the perihumeral muscles. Surgical drainage was performed, and cultures grew Enterococcus faecalis. The patient showed rapid clinical and laboratory improvement following appropriate antibiotic therapy. This case represents the second reported instance of enterococcal pyomyositis in a patient with RA. The findings highlight the potential cumulative immunosuppressive effect of combined disease-modifying antirheumatic drugs and corticosteroids as a predisposing factor. Clinicians should maintain a high index of suspicion for rare but serious infections such as pyomyositis in immunosuppressed patients presenting with focal muscle pain and systemic symptoms, as early diagnosis and prompt intervention are crucial for favorable outcomes.