Tuberculosis (cutaneous) and tuberculids

Exogenous TB

Primary inoculation TB is rare and develops in previously unsensitized adults following local trauma as in tattooing, ear-piercing, ritual circumcision or exposure to unsterilized surgical instruments. A firm, painless reddish-brown papule/nodule forms after 1–3 weeks, evolving into a shallow ulcer with undermined bluish margins with regional lymphadenopathy. The chancre may heal spontaneously in 3–12 months. Tuberculosis verrucosa cutis (TVC) presents as solitary, slow growing, painless verrucous plaque over exposed sites in individuals with moderate-to-high immunity against M. tuberculosis . Lymphadenopathy is uncommon.

Endogenous TB

Scrofuloderma (SCF) , the most common variant worldwide, occurs as a result of contiguous spread from an underlying primary focus, usually a lymph node, bone, and/or joints. It presents as painless swellings and discharging sinuses with undermined bluish margins. There is the possibility of acid-fast bacilli (AFB) in stained cytology smears/biopsy samples as well as positive culture is higher.

Lupus vulgaris (LV ) is the second most common variant and presents as single or multiple, well-defined, reddish-brown, irregular plaques that expand peripherally with prominent advancing margins and central atrophy/scarring. Untreated, chronic LV lesions may be complicated by gigantic size, deep tissue destruction, bony contractures, and malignancy.

Orifical TB is rare and generally seen in severely ill, immunodeficient patients. Lesions form around mouth, genital, or anal mucosae, following M. tuberculosis autoinoculation in patients with advanced intestinal or genitourinary tuberculosis.

Tuberculous gumma present as fluctuant non-tender subcutaneous nodules or abscesses forming ulcers with undermined margins in patients with poor immunity.

Acute military TB results from hematogenous dissemination of M. tuberculosis in severely ill immune-compromised patients (as in HIV/AIDS) with disseminated TB. Lesions are widespread erythematous to purplish papules, pustules, or vesicles that resolved spontaneously in 2–4 weeks.

Tuberculid

Tuberculid represent a cutaneous immunologic reaction to the presence of M. tuberculosis in patients with significant immunity. The diagnosis is based on evidence of an active or healed tubercular focus (lymph node, lungs, abdomen, etc.), tuberculoid histology on biopsy, negative culture, strongly positive tuberculin test, and response to antitubercular drugs.

Papulonecrotic tuberculid (PNT) is characterized by symmetrical, dusky red necrotizing papules and pustules over extremities, while lichen scrofulosorum (LS) is characterized by grouped, pin-head sized, skin-colored/erythematous, perifollicular papules over the trunk in children. Erythema induratum of Bazin (EIB) presents as slightly painful, erythematous to violaceous indurated plaques and nodules that tend to ulcerate over posterior and anterolateral aspects of the legs.