A 50-year-old woman who previously underwent a heart transplant presents to the clinic with nonpainful, nondraining erythematous nodules on her trunk and extremities. The nodules have developed over the course of 1 week. She is HIV negative and has no other significant medical history. Family history is unremarkable. The remainder of the physical examination is within normal limits, and the patient is otherwise asymptomatic.
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Disseminated atypical mycobacterial infections are caused by species of Mycobacterium other than M tuberculosis and M leprae. There are many species of Mycobacterium, and there are at least 30 species that do not cause tuberculosis or leprosy.1 Atypical mycobacteria are obligate aerobes that can be found in the environment in soil, water, vegetables, and dairy products, and on domestic animals.
Rapidly growing mycobacteria (RGM) usually grow in subculture within 1 week and include 3 clinically relevant species: M fortuitum, M chelonae, and M abscessus. Of this group, M abscessus is most commonly seen in clinical respiratory specimens, and M fortuitum is the most common form seen in nonrespiratory specimens. M fortuitum causes human infection primarily by direct inoculation, including primary skin and soft tissue infections, surgical wound infection, and catheter-related sepsis.2
Atypical mycobacteria infections are divided into 4 clinical syndromes2: pulmonary infection, especially in older patients; skin and soft tissue infections, which usually occur through direct inoculation; disseminated infection, especially in those with severe immunocompromise; and lymphadenitis, especially cervical lymphadenitis in children.
RGM are an uncommon cause of soft tissue infection. Signs and symptoms include crusted nodules and plaques (frequently with purple discoloration), recurrent abscesses, or chronic discharging sinuses. RGM infections have been associated with footbaths at nail salons and tattooing with contaminated ink.3 Disseminated disease is most commonly found in those with profound immunosuppression.
RGM must be distinguished from M tuberculosis because the presence of M tuberculosis requires public health tracking. Atypical mycobacteria are diagnosed by tissue culture. If atypical mycobacterial infection is suspected, the laboratory should be advised as growth requires a cool temperature. Polymerase chain reaction on swabs of ulcers or tissue biopsy is also possible.2
Treatment of atypical mycobacterial infection depends on the infecting organism and the severity of infection. RGM are not susceptible in vitro to antituberculous drugs, and treatment requires antimicrobial therapy based on susceptibility. Historically, clarithromycin has been the mainstay of oral therapy.1 Usually treatment consists of a combination of drugs.
Limited infection requires treatment with 2 agents via oral therapy for a minimum of 4 months. Monotherapy is not recommended because it may result in acquired resistance and treatment failure. Severe disease goes beyond localized skin involvement and requires parenteral therapy with at least 2 agents for 2 to 6 weeks, followed by oral therapy with 2 agents.1 Treatment duration is at least 6 to 12 months. Possible parenteral agents include amikacin, tobramycin, cefoxitin, imipenem, and levofloxacin. M abscessus is more difficult to treat and requires initial combination therapy with 3 agents. Possible surgery may be indicated when there is poor response to drug therapy or if there are significant disease-related complications.3 Aggressive debridement or removal of infected lymph nodes may be necessary. In severe cases, skin grafts may be needed.
Elizabeth Shane, BS, is a medical student at The University of Texas Health Science Center at Houston’s McGovern Medical School, and Maura Holcomb, MD, is a resident at Baylor College of Medicine in Houston.
- 1. Griffith D. Rapidly growing mycobacterial infections in HIV-negative patients. UpToDate. http://www.uptodate.com/contents/rapidly-growing-mycobacterial-infections-in-hiv-negative-patients. Updated January 15, 2015. Accessed March 10, 2016.
- 2. Bhambri S, Bhambri A, Del Rosso JQ. Atypical mycobacterial cutaneous infections. Dermatol Clin. 2009;27(1):63-73.
- 3. Ingram CW, Tanner DC, Durack DT, Kernodle GW Jr, Corey GR. Disseminated infection with rapidly growing mycobacteria. Clin infect Dis. 1993;16(4): 463-471.