Author: Vanessa Ngan, Staff Writer, 2003. Updated by Hon A/Prof Amanda Oakley, August 2015.
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
TB verrucosa cutis
Occurs after direct inoculation of TB into the skin in someone who has been previously infected with mycobacteria
Presents as a purplish or brownish-red warty growth
Lesions most often occur on the knees, elbows, hands, feet and buttocks
Lesions may persist for years but can clear up even without treatment
Persistent and progressive form of cutaneous TB
Small sharply defined reddish-brown lesions with a gelatinous consistency (called apple-jelly nodules)
Lesions persist for years, leading to disfigurement and sometimes skin cancer
Skin lesions result from direct extension of underlying TB infection of lymph nodes, bone or joints
Often associated with TB of the lungs
Firm, painless lesions that eventually ulcerate with a granular base
May heal even without treatment but this takes years and leaves unsightly scars
Chronic TB infection that has spread from the primary infection (usually in the lungs) to other organs and tissues via the bloodstream
Skin lesions are small (millet-sized) red spots that develop into ulcers and abscesses
More likely in immunocompromised patients, eg HIV, AIDS, cancer
The patient is generally sick
Prognosis is poor (many patients die even if diagnosed and treated)
Generalisedexanthem in patients with moderate or high degree of immunity to TB because of previous infection
Usually in good health with no identifiable focus of active TB in skin or elsewhere
Erythema induratum (Bazin disease) presents as recurring nodules or lumps on the back of the legs (mostly women) that may ulcerate and scar. It is a type of nodular vasculitis.
Papulonecrotic tuberculid results in crops of recurrent crusted skin papules on knees, elbows, buttocks or lower trunk that heal with scarring after about 6 weeks.
Lichen scrofulosorum is an extending eruption of small follicularpapules in young persons with underlying TB.
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)
Severe Mantoux test reactions (active TB)
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 localisedcutaneous TB is recommended.