January 2006

This 16-year-old boy presented to the clinic with a 1.5-X 2-cm soft, well-circumscribed nodule on his left cheek. There was no purulent drainage, warmth or erythema. It has been slightly tender to touch. It has been present for two months, but increased in size and darkened in color after minor trauma to the area. There is no associated lymphadenopathy. What do you think is the diagnosis?

Answer

This patient’s wound culture was positive for Mycobacterium fortuitum, an atypical mycobacterial infection. The patient was initially treated with oral clarithromycin, but did not improve. Oral trimethoprim-sulfamethoxazole was added to his regimen without improvement. Finally, oral levofl oxacin (Levaquin, Ortho-McNeil) was started, and it resolved symptoms. Duration of therapy was approximately three months. There are over a dozen species of Mycobacterium in the environment capable of causing cutaneous disease. They are found in water, wet soil, household dust, dairy products, cold-blooded animals, vegetation and human feces. Accidental transmission occurs through inhalation, ingestion or percutaneous penetration resulting in pulmonary, lymph node or skin disease. More atypical mycobacterial infections are being reported in both immunosuppressed and normal hosts. They should be considered in patients with indolent ulcers, nodules or plaques especially if there is a history of HIV infection.

M. fortuitum and Mycobacterium chelonae are two rapidly growing organisms commonly grouped together as the fortuitum complex. M. fortuitum is a saprophyte found in water, soil, dust and animals. Skin infections most commonly present as multiple subcutaneous nodules on the distal limbs or in a sporotrichoid pattern. Rarely, localized lymphadenitis can also be present. Other cutaneous manifestations include cellulitis, abscesses, nodules, sinuses and ulcers with subcutaneous necrosis and serosanguineous or purulent discharge. M. fortuitum can also cause noncavitary pneumonia, endocarditis, lymphadenitis and osteomyelitis.

Transmission occurs after trauma, contact with animals or contaminated medical equipment. Cutaneous infection can also occur from dissemination from an endogenous source, although this is less common.

Diagnosis is made by culture. Biopsy material must be grown on specific media at 30 to 33 degrees Celsius. Biopsy specimens of abscesses should be obtained from the wall rather than aspiration of purulent material.

Differential diagnosis of cutaneous M. fortuitum infection includes actinomycosis, other atypical mycobacteria, coccidioidomycosis, cryptococcosis, histoplasmosis, mycetoma, sporotrichosis, nocardiosis and tuberculosis.

Treatment of M. fortuitum consists of local and systemic therapy. Surgical débridement may be required, especially in extensive lesions. Antibiotic therapy should be based on culture sensitivities. Agents effective in treating M. fortuitum include amikacin, tobramycin, cefoxitin, sulfonamide, ciprofl oxacin and imipenem (Primaxin, Merck). Fluoroquinolones are contraindicated in children younger than 18 years of age. First-line antituberculous agents, such as rifampin or isoniazid, have no role in treatment. There is no standard duration of therapy. Treatment should last until all clinical lesions have completely resolved, which may take at least six months.

For more information:

• Dieudonne A, Oleske JM, Schwartz RA. Atypical mycobacterial infection. [e-medicine Web site] February 15, 2005. Available at: http://emedicine.com/ped/topic3034.htm. Accessed December 14, 2005.
• Ramos e Silva M, Ribiero de Castro, MC. Mycobacterial infections. In: Bolognia JL, Jorizzo J, Rapini R, eds. Dermatology. London: Mosby; 2003:1145-1164.
• Woeltje KF, Lessnau KD, Talavera F, et al. Mycobacterium fortuitum. [e-medicine Web site] October 17, 2005. Available at: http://emedicine.com/med/topic1534.htm. Accessed Dec. 14, 2005.