Atypical Presentation of MRSA Septic Arthritis with Concurrent Pyomyositis of the Calf Muscles in an Immunocompetent Adult.

INTRODUCTION

Concurrent pyomyositis and septic arthritis without systemic symptoms is uncommon and may delay diagnosis.

CASE REPORT: A 36-year-old immunocompetent male presented with isolated right knee swelling, without fever or trauma. Magnetic resonance imaging revealed joint effusion and myositis in surrounding muscles. Joint aspiration confirmed Methicillin-resistant Staphylococcus aureus septic arthritis. Despite intravenous antibiotics, a growing intramuscular abscess in the gastrocnemius was detected on serial ultrasound. Surgical drainage was performed. The patient was treated with IV vancomycin for 2 weeks, followed by oral linezolid, and recovered fully.

CONCLUSION

Pyomyositis should be considered in septic arthritis with atypical presentations. Serial imaging and inflammatory markers are essential for guiding treatment.