An unusual cutaneous infection caused by Mycobacterium marinum

Introduction. Mycobacterium marinum is a non-tubercular mycobacterium residing in fresh or salt water (in tropical or temperate areas); it is a fish and human pathogen, and in immunocompromised patients can cause severe cutaneous and subcutaneous infections.

Case presentation. A 46-year-old white man who underwent immunosuppressive therapy was admitted to our department in May 2016 for skin lesions previously diagnosed as ‘unusual erysipelas’. We rejected the hypothesis of erysipelas, due to the clinical features, and our diagnostic hypotheses were oriented towards sporotrichosis, atypical mycobacteriosis, cutaneous tuberculosis and cutaneous sarcoidosis. Histological examination performed after a skin biopsy was compatible with a diagnosis of sporotrichosis. However, PCR performed on fresh tissue demonstrated the presence of M. marinum.

Conclusion. The case reported is interesting for the unusual clinical localization and modality of infection. The patient became infected by contact with contaminated remains or in the sea, in a geographical area not endemic for M. marinum. The previous state of immunosuppression favoured infection; however, the presence of M. marinum in this area suggests a possible tropicalization of the water of the Mediterranean Sea. To our knowledge, this case is the only one reported in the literature with this modality of infection and in that geographical area.