Surgical resection of a cutaneous nodule in the left foot caused by mycobacteria

First submission on 18/01/13; last submission on 19/03/13; accepted for publication on 03/05/13; published on 20/06/13 1. Master’s in Biological Sciences; professor in Mycology, Microbiology and Parasitology at Universidade Regional Integrada (URI) Erechim; biochemical pharmacist. 2. Graduate student in Pharmacy at URI Erechim; Scientific Initiation scholarship at URI Erechim. 3. Doctor specialist in Dermatology. ABStrACt

Mycobacteria include important pathogens such as Mycobacterium turbeculosis and M. leprae. Approximately 150 species are indigenous in the human environment (7,8) . Several species of nontuberculous mycobacterium have been reported in the states of Mato Grosso do Sul and Rio de Janeiro, Brazil (13,15) .
Mycobacterium marinum is among the pathogenic mycobacteria. It was initially described in 1926 during an investigation into infectious diseases in marine fish (2) . It has worldwide distribution and it is generally associated with cutaneous and bone-articular lesions (9) . Moreover, it is accountable for approximately 150 new cases in the United States annually (5) .
M. marinum is a natural pathogen in ectothermic animals, including amphibians and fish. In the latter they cause systemic granulomatous disease. Diseases caused by mycobacteria are among the most prevalent in fish (9,14) . It is particularly worrying the fact that bacteria involved in fish bacteriosis are able to infect humans (4) . Human infections caused by M. marinum produce nodular or ulcerated cutaneous lesions in upper or lower limb extremities (12) .
Delayed diagnosis is common and invasion of deeper structures such as synovium, bursae and bone occur in approximately a third of the reported cases (12) . A rare case of long bone osteomyelitis has been described in an immunosuppressed patient (16) . The contamination usually occurs through direct contact with fish or contaminated water, generally in the presence of a pre-existing wound or trauma (1,4) .
The present study describes the clinical progression of a patient who presented a wound caused by a fish. The microscopic exam of the affected area revealed the presence of resistant acidfast bacilli (RAFB).

CASE rEPort
In February 2007, 51 year-old female patient reported a superficial would in the left foot caused by a fish known as tilapia.
The lesion was caused by trauma during fishing, which occurred in a city in the north region of Rio Grande do Sul, Brazil.
Fifteen days after the initial wound, the patient developed a small asymptomatic papule on the site. Two months afterwards, after trekking with sneakers, the lesion volume increased considerably, presenting a painful swollen erytematous nodule ( Figure 1). Shortly after the onset of these symptoms, a traumatologist raised the diagnostic hypothesis of bursitis and prescribed applying ice to the affected region concomitantly with the use of a non-steroid anti-inflammatory drug orally. The clinical progression is illustrated in Figure 1.  As the patient did not present any clinical improvement after prescribed treatment, microscopic, bacteriological and anatomopathologic exams were requested. Gram staining allowed to establish that there were no microorganisms in the site, though there were numerous leukocytes. Microscopic and bacteriological exams were negative. Moreover, there were no fungi in the direct exam and culture. The absence of microbiological findings led to RAFB screening through Ziehl-Neelsen staining, yielding positive results (Figure 2A and Figure 2B -Figure 2).
The patient received rifampicin 300 mg, which was administered every 12 hours during 3 days. Subsequently, the patient underwent total surgical excision ( Figure 1B). The anatomopathologic results from the surgical specimen revealed chronic central suppurative granulomatous dermo-hypodermal inflammation ( Figure 2C and Figure 2D). After surgical resection of the affected area, followed by epithelial grafts and hyperbaric treatment, the patient achieved full recovery with no relapses for five years and eight months ( Figure 1D).

DiSCuSSion
Based on the patient's clinical history, Mycobacterium marinum was considered the most probable infectious agent, which is found in a wide variety of aquatic habitats worldwide. Accordingly, people who work with aquaculture or have aquariums have a higher risk of acquiring this infection.
Most patients with infections caused by M. marinum respond to antimicrobial treatment, though prolonged treatments are sometimes required for several months (1,6,17) . A review study assessed the clinical progression of 63 cases and concluded that the most commonly prescribed antibiotics were clarithromycin, tetracycline and rifampicin (3) . The use of clarithromycin is effective for most patients with cutaneous infections (10) . Nonetheless, refractory cases requiring several antibiotics and surgical procedures have been reported (18) as well as cases in which the infection has led to death (11) .
The clinical progression of some cases reported by the literature is shown in the Table below. In clinical practice, the diagnosis of cutaneous infection by M. marinum is established on the basis of the clinical history, lesion features, microbiological exam and molecular techniques. The contact with fish and aquariums plays a major role in the differential diagnosis, hence the need to investigate the patient's exposure to aquatic habitats. The better understanding of this infection enables an early approach, which reduces the potentially high risk of deeper tissue involvement. Therefore, in this specific case, the total surgical excision of a unique mycobacterial lesion was the treatment of choice.