What is cutaneous tuberculosis?
Cutaneous tuberculosis (TB) is essentially an invasion of the skin by Mycobacterium tuberculosis, the same bacteria that cause TB of the lungs (pulmonary TB). Cutaneous TB is a relatively uncommon form of extrapulmonary TB (TB infection of other organs and tissues). Even in countries such as India and China where TB still commonly occurs, cutaneous outbreaks are rare (<0.1%).
Types of cutaneous TB
Several different types of cutaneous TB exist. Direct infection of the skin or mucous membranes from an outside source of mycobacteria results in an initial lesion called the tuberculous chancre. The chancres are firm shallow ulcers with a granular base. They appear about 2-4 weeks after mycobacteria enter through broken skin. The immune response of the patient and the virulence of the mycobacteria determine the type and severity of cutaneous TB.
|Types of cutaneous TB||Features|
|TB verrucosa cutis||
What tests are available?
The diagnosis is usually made or confirmed by characteristic histopathological features on skin biopsy. Typical tubercles are caseating epithelioid granulomas that contain acid-fast bacilli. These are detected by tissue staining, culture and polymerase chain reaction (PCR).
Other tests that may be necessary include:
- Tuberculin skin test (Mantoux or PPD test)
- Interferon gamma release assay blood test
- Sputum culture (it may take a month or longer for results to be reported)
- Chest X-ray and other radiological tests for extrapulmonary infection.
- Interferon gamma release assays (IGRA)
What is the treatment of cutaneous TB?
Patients with pulmonary or extrapulmonary TB disease need to be treated with antitubercular drugs. This usually involves a combination of antibiotics (isoniazid, rifampicin, pyrazinamide and ethambutol) given over a period of several months and sometimes years.
Patients with latent TB infection but no active disease may also be treated with antitubercular drugs to prevent development of active disease. See tuberculosis screening.
Occasionally surgical excision of localised cutaneous TB is recommended.