Mycobacterium marinum infection: a case report

Abstract

The infection by Mycobacterium marinum in humans is relatively uncommon. When it occurs, it mainly affects the skin, usually with a chronic, indolent and benign evolution. The diagnosis requires a high index of suspicion, and a significant delay may be observed between the first symptoms to the final diagnosis. This present case reports a M. marinum infection in an immunocompetent patient that had a chronic undiagnosed injury on the dominant hand for at least five years. The patient had several medical consultations, without proper suspicion, hampering adequate diagnostic investigation. Histopathology detected tuberculoid granulomas, but showed no acid-fast bacilli. The culture in appropriate medium and the polymerase chain reaction-restriction enzyme analysis (PRA)-hsp65 confirmed the diagnosis. Treatment with clarithromycin (1 g/day) for three months was effective. Although uncommon, this infection is a contact zoonosis. Therefore, it is important for clinicians to be aware of this diagnosis and properly guide preventable measures to professionals that are in risk group.

Keywords: Case report; Granuloma; Mycobacterium infections; Mycobacterium marinum.

Figure 1

Erythematous-brown plaque, hardened and rough, with some reddish-honey colored crusts on the dorsum of the fifth right finger, before treatment.

Figure 2

Skin biopsy - Histopathology. (a) Pseudocarcinomatous epithelial hyperplasia with amorphous material in the follicular epithelium, which is surrounded by intense infiltrates of lichenoid pattern (HE, original magnification 40×). (b) Chronic granulomatous inflammatory reaction of tuberculoid pattern with focus of fibrinoid necrosis and absence of acid-fast bacilli (Fite-Faraco, original magnification 200×).

Figure 3

Mycobacterium marinum culture on Löwenstein-Jensen medium, after 12 days of incubation at 26°C (78.800°F).

Figure 4

Evolution during and after treatment. (a) Dorsum of the fifth right finger, one month after the beginning of treatment. (b) Dorsum of the right finger, three months after initiation of treatment.