Cutaneous tuberculosis: A great imitator

Tuberculosis (TB) is still prevalent in many developing countries and can pose a new potential threat to global health due to international migration. As an uncommon form of extrapulmonary TB, cutaneous TB is complicated in its clinical manifestation, pathogenesis, and classification. Cutaneous TB can be divided into two major categories, true cutaneous TB and tuberculid, depending on the source of infection, the route of transmission, the amount of bacteria, and the immune state of the host. Clinical manifestations may include patches and plaques (lupus vulgaris, TB verrucosa cutis), macules and papules (acute miliary TB, papulonecrotid tuberculid, lichen scrofulosorum), nodules, and abscesses (erythema induratum of Bazin, tuberculous gumma), erosions, and ulcers (tuberculous chancre, orificial TB, scrofuloderma), mimicking diverse skin diseases. Uncommon localizations such as external genitalia, unusual presentations such as nodular granulomatous phlebitis, and coexistence with other morbidities such as Behçet disease and acne inversa or hidradenitis suppurativa deserve special attention. Treatment of both true and tuberculid cutaneous TB follows the same drug regimens of the World Health Organization's recommendation for treatment of new cases of pulmonary TB. Erythema induratum of Bazin may need longer treatment duration and adjuvants such as dapsone, potassium iodide, doxycycline, and corticosteroids to tackle inflammation. Misdiagnosis and undertreatment in daily practice are likely, and contemplation of this classic great imitator in dermatology is warranted.