Gouty finger flexor tenosynovitis with urate milk remarkably similar to infection: a case-based review.

Gout attacks and tophi due to hyperuricemia are common, but rarely occur in extraarticular flexor tendons. Milky white fluid containing urate crystals, referred to as urate milk, may incidentally accumulate in the joint cavity and tophus of patients with gout. We report a rare case of gouty flexor tenosynovitis in the finger, characterized by urate milk, which closely resembled pyogenic tenosynovitis. A 54-year-old man with a history of gout attacks presented unprovoked right ring finger pain with marked erythema, swelling, and limited range of motion of the palmar side of the proximal interphalangeal (PIP) joint. He experienced gout attacks without tophus in both feet once a year since the age of 30 years. At the time of the initial onset, the patient took uric acid-lowering drug just for one month for hyperuricemia, but then stopped outpatient treatment and had been using non-steroidal anti-inflammatory drugs (NSAIDs) only during attacks. No abnormalities were observed on radiographs, and magnetic resonance imaging (MRI) showed T1-low and T2-very high-intensity regions from precisely above the flexor tendon to subcutaneously at the PIP joint level. Blood examination revealed C-reactive protein level of 2.5 mg/L, white blood cell count of 8.1 × 10⁹ /L, and uric acid level of 666 µmol/L (normal range ≦ 360 µmol/L). The operation was performed for the patient suspected of suppurative flexor tenosynovitis. A milky white fluid overflowed subcutaneously, and multiple gouty tophi were observed on the tendon sheath. The diagnosis of gouty flexor tenosynovitis was made based on the absence of bacteria on culture and uric acid crystals on optical microscopy. Histopathological examination revealed an accumulation of multinucleated giant cells around the amorphous deposits characteristic of gouty tophi. Gouty tenosynovitis with urate milk should be considered in cases presenting a history of gout attacks, hyperuricemia, and high T2 signal intensity on MRI, such as subcutaneous pus accumulation in the clinical picture of infection.