Cutaneous tuberculosis (CTB) is caused by M tuberculosis, Mycobacterium bovis, and the Bacillus Calmette–Guérin (BCG) vaccine. It is exceedingly rare, only occurring in 1%-2% of extrapulmonary TB cases. CTB is more common in children, pregnant individuals, and HIV-infected persons. Cutaneous manifestations of TB can be subclassified into 4 categories.
Exogenous Sources: Primary inoculation TB occurs at sites of trauma, abrasions, or wounds or at mucous membranes.
- In patients with no immunity against TB, a scab or chancre forms at the wound site and can be associated with regional lymphadenopathy after several weeks. Lymph nodes can eventually suppurate, abscesses can form, and fever and pain can develop.
- In previously sensitized individuals, primary inoculation can lead to tuberculosis verrucosa cutis (warty tuberculosis) and is not usually associated with systemic symptoms.
- Scrofuloderma results from involvement of skin overlying a contiguous TB focus, usually a lymph node, bone, joint, or lacrimal gland. It is the most common form of CTB in children.
- Orificial TB is a rare mucosal autoinoculation TB from pulmonary, genitourinary, or intestinal disease shedding organisms that seed the adjacent orifices.
- Lupus vulgaris results from hematogenous spread and is a progressive form of CTB seen in individuals with prior sensitivity and low immunity.
- Tuberculous gumma (metastatic tuberculous abscess) is a rare form of hematogenous TB.
- Acute miliary TB is a rare but life-threatening form of hematogenous TB seen in patients with low immunity.
- Micropapular (lichen scrofulosorum)
- Papular (papulonecrotic tuberculid)
- Nodular (erythema induratum). Erythema nodosum can be also seen in pulmonary TB. Lesions are typically asymptomatic but may be painful. Localized adenopathy may occur.
All forms of CTB including tuberculids require systemic treatment. Without treatment, lesions can persist for months to years. The prognosis of miliary TB is often poor.