Infections are usually acquired from the environment. The initial lesions develop in the skin where they were inoculated. The clinical appearance is quite variable. Some have thickened lumps or plaques that cause no symptoms and usually grow slowly. Some ATM may cause ulcers.
Mycobacteria are rod-shaped bacteria. Their cell walls are surrounded by a thick waxy coat, which protects them in harsh environments. Mycobacteria are highly resistant to germicides because of their thick protective cell wall. They are highly resistant to drying, and can exist outside the body without moisture for long periods.
A history of hobbies such as working with tropical fish that may carry mycobacterium marinum can help pinpoint the diagnosis of lumps developing. The geograpical location also provides clues. Living in subtropical climates with wetlands the presence of a minor injury on the extremities that allows the bacterium in may result in the development of a slowly growing inflammation that ulcerates causing a Buruli or Bairnsdale ulcer. These occur in Northern Australia and Africa. Some ATM infections may follow injections, catheterisations or after surgery
The diagnosis is usually made from a biopsy with histology. Culturing the tissue to grow the bacteria and special tests such as polymerase chain reaction that identifies the presence of the genetic material from mycobacterium tuberculosis.
The treatment of cutaneous mycobacterial infections depends on the species and sensitivity to antibiotics. Atypical mycobacteria are less sensitive to anti-tuberculous treatments but may be responsive to some chemotherapeutic agents or other antibiotics. Hence, species identification is important prior to instituting treatment. Treatment regimens are usually prolonged and often more than one medication may be given to minimise the risk of developing drug resistance.
If patients are under nourished, have HIV or are on medications that cause suppression of their immune system these infections may be more extensive and harder to treat.
This information has been written by Mia Yue Yu and Dr Monisha Gupta
Published: 3rd July 2019
