BACKGROUND The diagnosis of gout can be problematic when the presentation is atypical and serum uric acid is borderline elevated. Demonstration of monosodium urate (MSU) crystals in fine needle aspiration (FNA) smears from nodular masses clinically suspected to be tophi establishes the diagnosis unequivocally.
Of the 7 cases in this study, 4 were suspected clinically to have gouty tophi. Giant cell tumor of tendon sheath, giant cell tumor of bone and metastatic tumor with multicentric involvement of bone were the clinical diagnoses in 1 case each. Serum uric acid levels high enough to be in the diagnostic range for gout were reported in 3 cases, within normal limits in 3 cases and low in 1 chronic alcoholic patient. Bright field microscopy of FNA smears revealed singly scattered or stacks of MSU crystals with variable number of inflammatory cells, with or without foreign body giant cells in 6 cases. In 1 patient, FNA showed stacks of MSU crystals only. Characteristic birefringence of MSU crystals was observed on polarizing microscopy.
FNA demonstration of MSU crystals on polarizing microscopy can easily establish the nature of the nodules in and around the joints and in soft tissue as gouty tophi and is thus an investigation differentiating this lesion from other masses clinically simulating it.