Eosinophilic Synovitis Masquerading as Septic Arthritis in a Pediatric Patient: A Case Report and Diagnostic Insights.

Introduction: Eosinophilic synovitis, though rare, can closely mimic septic arthritis in children, often complicating diagnosis. This inflammatory condition is typically linked to allergic reactions or parasitic infections, though idiopathic cases have been documented.

Case report: We describe a 4-year-old boy initially diagnosed with septic arthritis of the knee. The patient underwent arthrotomy, and synovial fluid analysis surprisingly revealed significant eosinophilia. Histopathology confirmed eosinophilic synovitis. Following a 3-week course of diethylcarbamazine (DEC), the patient achieved full recovery with no recurrence.

Conclusion: This case emphasizes the importance of synovial fluid analysis in pediatric monoarticular joint swelling, as eosinophilic synovitis should be considered in differential diagnoses to avoid misdiagnosis and unnecessary interventions.