Cytology of urate milk in gouty arthritis: a case report

BACKGROUND: Synovial fluid (SF) analysis is a useful investigative procedure in the evaluation of various types of arthritides, including gouty arthritis. Rarely, gouty arthritis may present with effusion containing thick, milky white fluid. We report a case of gouty arthritis, describing cytologic features of the urate milk. CASE: A 42-year-old man presented with pain and swelling of multiple joints of long duration. Approximately 3 mL of milky white SF was obtained for white blood cell (WBC) count, with a clinical diagnosis of septic arthritis. Due to the gross nature of the sample, the WBC count could not be performed; however, cytologic examination of the sample revealed a massive amount of classic, needle-shaped urate crystals on routinely stained May-Grünwald-Giemsa smears, favoring a cytologic diagnosis of gouty arthritis. CONCLUSION: Gouty synovitis occasionally presents with thick, milky white urate-laden synovial effusions, which clinically may be mistaken for septic arthritis. This gross nature of the specimen may interfere with the performace of a WBC count on SF samples.