[Ultrasound-guided synovial biopsy].

A 47-year-old female presented with arthritis in the left hand's PIP III. Her symptoms were negative for connective tissue disease or spondyloarthritis, but she had HIV and hepatitis B. Initial tests showed no systemic inflammation or abnormal antibodies, and radiology revealed no bony changes. Despite a successful initial treatment with a Kenacort injection, arthritis recurred in both hands. A synovial biopsy via ultrasound revealed gout tophi, confirmed by dual-energy CT showing urate crystals in the soft tissue. Synovial biopsy is an effective, minimally invasive diagnostic tool for undifferentiated arthritis when other tests are inconclusive. Though puncture analysis remains the gold standard, it was not possible in this case due to lack of joint effusion.