Local and disseminated infections caused by Mycobacterium marinum: an unusual cause of subcutaneous nodules.

Mycobacterium marinum is a free-living, nontuberculous, photochromogenic mycobacterium, which can cause opportunistic infections in humans. It can cause infection through the skin that has undergone minor trauma, as the portal of entry from contaminated water, fish tanks and nonchlorinated swimming pools. It can cause skin lesions, which are either single, papulonodular lesions, confined to an extremity or may resemble cutaneous sporotrichosis. This infection can also cause deeper infections including tenosynovitis, bursitis, arthritis, and osteomyelitis. Disseminated infections and visceral involvements have been reported in immunocompromised patients. We describe 3 patients seen in Geisinger Medical Center from 2000 to 2005 in whom the diagnosis of M. marinum infection was made. All 3 patients described had sporotrichoid nodular lesions, one had a preceding minor trauma, one was initially misdiagnosed as having rheumatoid arthritis and developed disseminated infection requiring prolonged treatment, and one had direct exposure to fish and fish tank. M. marinum infection is frequently misdiagnosed probably due to its rarity of occurrence, indolent presentation and difficulty in isolation and culture. Recognition depends on a high index of suspicion and eliciting a history of aquatic exposure. Diagnosis usually requires tissue biopsy for histopathologic examination and culture.