Mycobacterium marinum causing tenosynovitis. 'Fish tank finger'.

Mycobacterium marinum is an unusual atypical mycobacterium with low pathogenicity for humans in comparison with Mycobacterium tuberculosis. Among the non-tuberculous mycobacterial pathogens, Mycobacterium marinum is the most common pathogen to cause skin infections. Mycobacterium marinum infection causes chronic cutaneous lesions and in some cases deeper infections such as tenosynovitis, septic arthritis and rarely osteomyelitis. We report the case of a male patient presenting with tenosynovitis of the distal upper extremity secondary to Mycobacterium marinum infection.