Atypical musculoskeletal manifestations on flexor hallucis longus tendon of gout causing tarsal tunnel syndrome in diabetic patients: A case report

RATIONALE: Deposition of tophus is a common feature in chronic gout; however, signs and symptoms are not always well-pronounced in cases of uncommon sites. We report a rare case with a tophaceous tendonitis on the flexor hallucis longus (FHL) tendon with tarsal tunnel syndrome (TTS). This is the first surgical case of TTS by gouty tophi in FHL. PATIENT CONCERNS: A 55-year-old woman presented with a 6-month history of mild discomfort at the right foot, which gradually worsened in the past 3 weeks. The patient visited our outpatient clinic due to persistent and aggravating foot pain and swelling around the tarsal tunnel. DIAGNOSIS: The patient was diagnosed with hyperuricemia and diabetes mellitus with chronic kidney disease, and did not receive regular antigout treatments. Paresthesia was found along the distribution of medial and plantar nerve and tinel test was positive on tarsal tunnel. Biochemical examination showed she had raised serum uric acid (10.6 mg/dL) and decreased estimated glomerular filtration rate (69 mL/min/1.73 m(2)). Conventional radiography examination showed negative pathology except soft tissue swelling. Magnetic resonance imaging revealed a fusiform mass within the FHL tendon and fluid collection around tarsal tunnel. INTERVENTIONS: Surgical exploration was performed to remove the mass. Inflammation fluid exploded out from FHL tendon sheath, which was later proven to have infiltration of monosodium urate crystal. Superficial dissection revealed a white chalky mass and posterior tibial nerve was significantly compressed by the tophus mass. OUTCOMES: The mass was removed and the symptoms were relieved at immediate postoperative period. LESSONS: A tophaceous tendonitis on FHL tendon can cause TTS and surgical decompression of the gout lesion can reduce the symptoms.