Rare case of Mycobacterium marinum in a patient presenting with tenosynovitis.

A 72-year-old man presented with tenosynovitis of the left hand's extensor tendons that had been present for several months. He was initially treated with corticosteroids, first by local injection then systemically, but with no effect. When re-evaluated, the patient had developed a rash, and the symptoms had spread locally to surrounding structures. At this point, the patient added to the medical history that he had been stung by a sculpin a month before the debut of symptoms. Based on this, the patient's involved area was biopsied, and subsequent microbiology findings proved consistent with Mycobacterium marinum infection. By the time of diagnosis, the patient had soft tissue involvement, arthritis and osteomyelitis with an overlying rash. This case emphasises the need for reassessment when treatment is not effective and for further investigations of the medical history to establish the correct diagnosis and treatment.