BACKGROUND/ INTRODUCTION: Septic arthritis present as an acute monoarticular arthritis and is highly suspected in patients with risk factors including DM, ESRD, and bacteremia. As a result, empiric antibiotics are usually started prior to definitive diagnosis. But crystal induced arthropathies closely mimic septic arthritis in their presentation. This case highlights the importance of early arthrocentesis to avoid unnecessary antibiotic treatment.
CASE PRESENTATION: 50-year-old female on antibiotics for MSSA bacteremia presented due to acute onset left hip pain, swelling and decreased range of motion. No trigger was present. PMH included HTN, T2DM and ESRD on HD. She denied fever, chills or any other systemic symptoms. Labs demonstrated WNL leukocytes. CT scan showed moderate size left femoral acetabular joint effusion with surrounding synovial hyperemia and bilateral iliopsoas hematoma. Based on recent history of MSSA working diagnosis was made as septic arthritis which prompted us to start her on antibiotics. arthrocentesis was performed and fluid was sent for studies after starting her on antibiotics. Fluid shows mild inflammation with no concern for septic arthritis. Suspicion was still high for septic arthritis given the recent diagnosis of MSSA, and it was thought that fluid studies were negative as patients have been on long term antibiotics. The case took an interesting turn when fluid studies showed bifringent crystals consistent with CPPD; Pseudogout and G/S and culture remained negative. The patient started and responded well to steroids.
DISCUSSION: This case shows how pseudogout mimics gout, especially in patients having risk factors for septic arthritis. Recent MSSA bacteremia and acute onset of hip symptoms justifiably raised concerns for septic arthritis prompting early antibiotic initiation. However, proper diagnostic tests lead to diagnosis. CPPD is underdiagnosed with a prevalence of 4-7% of the adult population in USA and Europe and is rarely seen in patients younger than 60 years. It is commonly presented as a painful and swollen joint which makes it difficult to distinguish from septic arthritis. Synovial fluid analysis and crystal studies are the mainstay for diagnosis and distinguishing it from septic arthritis.
TEACHING / LEARNING POINTS: Arthrocentesis and fluid studies should be done early, ideally before antibiotic initiation, in cases concerning arthritis and having effusion to r/o aseptic arthritis. As aseptic arthritis can get masked under septic arthritis.