An immunocompetent 28-year-old male aquarium store employee presented with 1 month of intermittent epistaxis. A bleeding granulomatous lesion was identified over the right nasal septum (Figure 1). Histopathology from the incisional biopsy revealed granulomatous inflammation with the presence of acid-fast bacilli (Figure 2). Culture of the homogenized specimen on Middlebrook 7H11 agar after 14 days displayed white clones of non-tuberculous Mycobacterium (NTM) that turned brilliant yellow upon light exposure (Figure 3). Polymerase chain reaction (PCR) amplification of the 65-kDa heat shock protein gene with restriction enzyme analysis using BstE II and Hae III confirmed the diagnosis of Mycobacterium marinum infection. The lesion regressed completely with 3 months of doxycycline treatment.
Fish tank granuloma is a rare granulomatous skin infection caused by Mycobacterium marinum, an opportunistic NTM, commonly found in aquatic environments.1 Extremities are most frequently affected; nasal cavity infection is seldom reported. The diagnosis is generally based on a history of aquatic exposure (occupational or recreational), histopathology of granulomatous inflammation with or without the presence of acid-fast bacilli, and a slow-growing photochromogenic NTM incubated at low temperature (28–30°C). Furthermore, PCR facilitates an early identification of Mycobacterium marinum infection. Superficial lesion sometimes resolves spontaneously, but several months of antimicrobial drug are usually necessary. Various monotherapies, including doxycycline, are effective.2
Rallis E, Koumantaki-Mathioudaki E, 2007. Treatment of Mycobacterium marinum cutaneous infections. Expert Opin Pharmacother 8: 2965–2978.