Amputation of a finger in a patient with multidrug-resistant Mycobacterium marinum skin infection.

Mycobacterium marinum is the etiologic agent of fish tank granuloma. The clinical course is usually benign: spontaneous healing is possible within weeks or months. However, fish tank granuloma is sometimes resistant to several antibiotics. We report a case of M. marinum infection of a finger in a 73-year-old cook. The disease was resistant to a number of antibiotics and required the amputation. The history of this patient testifies that M. marinum can be resistant to several antibiotics and that skin infections can be sometimes so severe as to require the amputation of a finger.

Introduction

Mycobacterium marinum is an acid-fast, aerobic, nonmotile, non-sporulating, photochromogen bacterium. It possesses a thick cell wall made up of wax (40%–70%) and lipids (25%–30%). M. marinum growth is usually slow: 2–6 weeks on Löwenstein–Jensen medium, at the temperature of 25°C–33°C. In culture, with a light source, the color changes from white to yellow because of the accumulation of β-carotene crystals.1,2 M. marinum has a worldwide diffusion, mainly in temperate and hot-humid climates. Its natural habitat is fresh and salt water. Penetration of M. marinum in the skin occurs through abrasions or excoriations. Incubation period is usually 3 weeks; however, 35% of patients has an incubation period ≥30 days.3 M. marinum is the etiologic agent of fish tank granuloma. Hands (fingers and dorsum), wrists and forearms are most frequently involved.3–9 Fish tank granuloma is characterized by four clinical presentations: type I: single erosive or ulcerative or crusted or verrucous papules, nodules and plaques; type II: more or less numerous and widespread lesions, often with a sporotrichoid distribution (multiple nodules along superficial lymphatics; regional lymphadenopathy is possible); type III: deep infections (bursitis, tenosynovitis, arthritis, osteomyelitis), with or without skin involvement; and type IV: widespread or disseminated lesions, systemic involvement and bacteremia, almost exclusively in immunocompromised patients.5,8,10–14 In types I and II, the clinical course is benign: spontaneous healing is possible within weeks or months;8,11,13 however, scar formation and reinfection, because of no permanent immunity, are possible. We report a case of type I M. marinum infection of a finger which was resistant to a number of antibiotics and required the amputation.

Case report

A 73-year-old Caucasian cook was admitted because of painful swelling, ulcers and crusts located at the left index finger. The patient stated that she was in good general health, except for mild essential arterial hypertension. Furthermore, the patient stated that the swelling had appeared 2 years earlier, followed, 6 months later, by the appearance of the ulcers. She was subjected to a biopsy at a dermatological center, with diagnosis of mycobacteriosis, although cultural examinations were negative for mycobacteria. The patient was treated with minocycline (100 mg/day for 3 months). However, this therapy was stopped because of both clinical failure and appearance of headache, dizziness and tinnitus. The patient was unsuccessfully treated at a second center with doxycycline (100 mg/day for 3 months) and nonsteroidal anti-inflammatory drugs. She subsequently went to a third center, where it was decided to use rifampicin (600 mg/day) and ethambutol (400 mg/day) for 4 months; however, no clinical remission was observed. When the patient was admitted at our hospital, dermatological examination revealed a severe erythematous swelling involving the left index finger. A roundish ulcer, of 0.8 cm diameter, with fibrinous bed and well-defined borders, and a round crust, of 0.7 cm diameter, were also visible at the medial and medial-lower surface of the finger, respectively (Figure 1). The patient complained of severe pain. General physical examination did not show anything pathological: in particular, no axillary lymphadenopathy was recorded. Laboratory examinations revealed leukocytosis (10,800 leukocytes/mm3), and increase in erythrocyte sedimentation rate (49 mm at the first hour), C-reactive protein (9 mg/dL) and α1-acid glycoprotein (4.1 mg/mL). All the other laboratory tests, including immunological tests, were within normal ranges or negative. X-rays showed a mild involvement of the periosteum of the second phalanx. Ultrasonography showed a dermal and subcutaneous swelling. Neurological examination, which was necessary in order to understand the nature of the severe pain reported by the patient, was negative. We performed a new biopsy. Histopathologic examination showed tubercular-like granulomas, with some Langhans cells and an inflammatory infiltrate with lymphocytes and neutrophils. Two out of three cultures were positive for M. marinum. PCR confirmed that the causative agent was M. marinum. Mycological examinations were negative. In vitro drug susceptibility testing was not performed. This was decided because, in our experience, based on ~60 patients with M. marinum skin infections, in vitro sensitivity was rarely correlated to in vivo sensitivity. The patient was treated with clarithromycin, according to a regimen we recently proposed (500 mg/day for 10 consecutive days/month for 5 months);15 oral diclofenac (100 mg/day) was added. This therapy induced only a slight improvement of the clinical picture; in particular, the patient complained of severe pain. She was therefore sent to a plastic surgery unit, where it was decided to perform the amputation of the finger. No additional antibiotic therapy was prescribed. We did not examine the patient anymore, but her surgeons stated that the follow-up (36 months) was negative.

Figure 1

Erythematous swelling, ulcer and crust located at the left index finger.

Written informed consent has been provided by the patient to have the case details and the accompanying image published.

Discussion

M. marinum skin infections can sometimes be considered as occupational diseases. However, they have been exceptionally reported in cooks.16–18 The patient we have described showed to be resistant to a number of antibiotics, including clarithromycin, which is, in our personal experience, the most effective antibiotic for the treatment of fish tank granuloma.15 However, according to literature data, M. marinum is often resistant, both in vitro and in vivo, to several antibiotics.13 In addition, in vitro sensitivity is not always correlated to in vivo sensitivity.13 In conclusion, no established therapy of choice does exist, and no therapeutic studies based on large groups of patients have been published.13 As previously mentioned, in this patient it was necessary to perform the amputation of the involved finger. This was also decided because of the severe pain reported by the patient. To our knowledge, six cases of amputation of a finger because of M. marinum infection were reported in the literature.9,19–23 In all cases, the infection was resistant to several antibiotics: isoniazid, rifampicin and ethambutol;19 rifampicin, ethambutol, clarithromycin and doxycycline;21 clarithromycin;22 and clarithromycin, moxifloxacin and ceftaroline.23 In addition, in one patient, destruction of the metacarpophalangeal joint capsule, flexor and extensor tenosynovitis, metacarpal and proximal phalanx bone destruction and abscess were recorded.19 In other two patients, amputation was considered as necessary because of osteomyelitis followed by fractures20 and flexor tenosynovitis,22 respectively. Finally, an amputation was performed because of methicillin-resistant Staphylococcus aureus superinfection.9 In our patient, bursitis, tenosynovitis, arthritis and osteomyelitis were not detected. The history of this patient testifies that M. marinum can be resistant to several antibiotics and that skin infections can be sometimes so severe as to require the amputation of a finger.