Atypical mycobacterial infection

Author: Vanessa Ngan, Staff Writer, 2003. Reviewed and updated by Dr Amanda Oakley Dermatologist, Hamilton, New Zealand; and Vanessa Ngan, Staff Writer; June 2014.

What is atypical mycobacterial infection?

Atypical mycobacterial infections are infections caused by a species of mycobacterium other than Mycobacterium tuberculosis, the causative bacteria of pulmonary TB and extrapulmonary TB including cutaneous TB; and Mycobacterium leprae, the cause of leprosy.

Atypical mycobacteria may cause many different types of infections, which are divided into the following four clinical syndromes:

Skin infection tends to result in crusted nodules and plaques. Abscesses may develop in skin and bone infection.

What causes atypical mycobacterial infection?

There are many different species of mycobacterium. To date at least 30 species of mycobacteria that do not cause tuberculosis or leprosy have been identified. Some of those causing atypical mycobacterial infections include:

Mycobacterium avium-intracellulare and Mycobacterium kansasii primarily cause lung disease similar to pulmonary TB, whilst Mycobacterium marinum, Mycobacterium ulcerans, Mycobacterium fortuitum and Mycobacterium chelonae cause skin infections.

What are the clinical features of atypical mycobacterial infection?

The clinical features of atypical mycobacterial infection depend on the infecting mycobacteria.

Mycobacterium avium-intracellulare

Mycobacterium kansasii

Mycobacterium marinum

Mycobacterium ulcerans

Mycobacterium chelonae

Mycobacterium abscessus

Mycobacterium fortuitum

See more images of atypical mycobacterial infections ...

How is atypical mycobacterial infection diagnosed?

Atypical mycobacteria are diagnosed on culture of tissue. Specific conditions are required, such as cool temperature, so the laboratory must be informed of the clinician's suspicion of this diagnosis. The infections have specific pathological features on skin biopsy.

Other diagnostic tools used include radiographic imaging studies and more recently, polymerase chain reaction (PCR) testing on swabs of ulcers or tissue biopsies.

What is the treatment of atypical mycobacterial infection?

Treatment of atypical mycobacterial infections depends upon the infecting organism and the severity of the infection. In most cases a course of antibiotics is necessary. These include rifampicin, ethambutol, isoniazid, minocycline, ciprofloxacin, clarithromycin, azithromycin and cotrimoxazole. Usually treatment consists of a combination of drugs.

Consider the following points when treating atypical mycobacterial infections with antibiotics:

Surgical removal of infected lymph nodes and aggressive debridement of infected skin lesions is sometimes necessary. In severe cases, skin grafts may be necessary to repair the surgical wound.

Some infections will heal spontaneously, leaving a scar (which is often very unsightly).

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