Clinical, Dermatoscopical and Laboratory Essentials of Fish Tank Granuloma

In immunocompetent individuals Mycobacterium marinum (M. marinum) infection usually presents with localized skin lesions, better known as “swimming pool granuloma” or “fish tank granuloma” (FTG). When establishing the diagnosis of FTG, doctors encounter several problems in the clinical practice: granulomas are detected in less than two thirds of biopsies and acid-fast bacilli are identified only in a minority of cases. Majority of disseminated and aggressive FTG forms are unrecognized at the beginning, and occur in immunosuppressed patients, including organ transplant patients. Functional impairment or even amputation of the extremity, visceral involvement and lethal outcome have been reported. Although more than one thousand cases of FTG have been reported worldwide, dermatoscopy of FTG, as a diagnostic aid, has not been reported yet. Presenting the case of FTG of recent onset where, guided by dermatoscopy, microorganisms were isolated and identified from the biopsy material, we summarize the essentials of clinical and laboratory diagnostics of M. marinum infection.