‘Finding Gory’—bringing home an unwanted aquatic traveler

CASE PRESENTATION

A 12-year-old girl was referred to our clinic with a chronic, indolent swelling and ulceration on her right foot.

Her symptoms started while vacationing in Hawaii 6 months prior. She recalled ‘stepping on something’ while walking in the ocean resulting in a small abrasion to the plantar side of her right foot. Over subsequent weeks she developed erythema and swelling around the abrasion. An x-ray of the foot 3 weeks after the injury was unremarkable and no treatment was initiated.

Over subsequent months the lesion became more demarcated and migrated medially and dorsally. She noticed satellite lesions developing. She had progressive discomfort with walking due to pain at the site of the lesions but remained systemically well. She received a 10-day course of oral cephalexin at weight appropriate dose in the community approximately 4 months after the initial injury with no improvement. Bacterial cultures of superficial wound swab taken at 4 months were negative. Her past medical history was unremarkable. She was on no regular medications and had no history of immunosuppression.

On examination she had an open wound with granulation tissue and serous drainage surrounded by satellite lesions in a well demarcated, circular pattern (Figure 1). MRI showed no foreign body and no evidence of osteomyelitis. Wound biopsy was sent for routine bacterial cultures which were, again, negative. Histopathology in conjunction with additional microbiological testing confirmed the pathogen and appropriate treatment was initiated.

Figure 1.

Lesions at the time of referral.

DISCUSSION

Mycobacterial staining of the wound specimen was done at the time of the biopsy and revealed 1 + acid fast bacilli (AFB). Rapid nucleic acid testing for Mycobacterium tuberculosis complex was negative. Histopathology revealed abscess with granuloma formation. Provisional diagnosis of Mycobacterium marinum infection was made based on the AFB stain, histopathology and clinical history. Culture growth occurred after 3 weeks of incubation; the organism was confirmed using polymerase chain reaction testing. Treatment with oral rifampin and sulfamethoxazole-trimethoprim was initiated, pending culture confirmation. Sulfamethoxazole-trimethoprim was subsequently replaced with clarithromycin due to slight neutropenia. At the end of treatment 3.5 months later she had small residual violaceous lesions that were flat and no longer painful (Figure 2).

Figure 2.

Lesions after 3.5 months of treatment.

M. marinum is a slow growing, nontuberculous mycobacterium (NTM) carried by fish and shellfish. Infection in humans ranges from cutaneous lesions to tenosynovitis, septic arthritis, osteomyelitis and rarely disseminated disease. Portal of entry is usually via skin abrasion that has become infected through direct handling of aquatic organisms or with inoculated water. Risk factors include occupational exposures such as working at aquariums or fish markets, hence the common name ‘fish tank granuloma’. Immunocompromised status, especially treatment with TNF inhibitors, can result in more extensive disease (1,2).

Cutaneous lesions develop several weeks to months after the initial exposure. Cellulitis is followed by nodular and ulcerated lesions. A characteristic sporotrichoid lymphocutaneous spread (subcutaneous nodules that progress along dermal and lymphatic vessel) has been reported in around 20% patients (2).

It may take several months before appropriate diagnosis is made due to low level of suspicion among health care providers, specialized laboratory requirements required for microbiological confirmation and the slow growing nature of the organism. Differential diagnosis for indolent cutaneous lesions includes other mycobacterial infections, sporotrichosis, erysipeloid, nocardiosis and leishmaniasis. Noninfectious causes including pyoderma gangrenosum, vasculitis and malignancy should be considered. Exposure to fresh or marine water environments can also be associated with other soft tissue bacterial infections (e.g., Vibro and Aeromonas spp.) although these tend to have a much more rapid, and potentially life-threatening clinical course (3).

Ziehl-Neesen (ZN) staining for AFB has detection rates between 15 and 30% (4–6) and cannot differentiate between M. marinum or other mycobacteria. Cultures generally show growth within a month of incubation. Granuloma formation is a characteristic histopathology finding although it is not pathognomonic for a mycobacterial infection.

There is no established treatment regimen. Dual therapy for a total of 3 to 4 months in uncomplicated infections is recommended; the most commonly mentioned regimens are rifampin + clarithromycin, rifampin + ethambutol or clarithromycin + ethambutol (7,8). No acquired antibiotic resistance has been reported (8). Involvement of deeper structures has been associated with antibiotic treatment failure and appropriate imaging along with surgical debridement should be considered (7).

CLINICAL PEARLS

• M. marinum soft tissue infection is characterized by indolent nodular and ulcerated lesions that usually involve the extremities and may progress in a sporotrichoid pattern.

• Careful history eliciting exposure to water and/or aquatic organisms is required to raise the level of suspicion for M. marinum as a causative organism and initiate appropriate investigations and treatment. Consultation with an infectious disease specialist is recommended.

• M. marinum soft tissue infections respond well to prolonged course of oral antibiotics. Involvement of deeper structures may require surgical debridement.