Cutaneous Manifestation of Tuberculosis

Cutaneous tuberculosis (CTB) is an uncommon form of extrapulmonary tuberculosis (TB). It is characterized as an invasion of the skin by Mycobacterium tuberculosis and, less commonly, Myco- bacterium bovis and the bacilli Calmette-Guerin vaccine. Cutaneous TB is rare despite the high prevalence of TB worldwide. The highest in- cidence of CTB is in underdeveloped, resource-poor countries. With some exceptions, lupus vulgaris (LV) is the most common form. Cu- taneous TB manifests a wide spectrum of clinical presentations, and current classification systems are based on the route of transmission and the immunologic state of the host. The exogenous (or primary) form of CTB occurs via traumatic direct inoculation of M. tuberculosis into the skin or mucous membranes leading to primary cutaneous TB, TB verrucosa cutis, and rarely LV. The endogenous (or secondary) form of CTB occurs through lymphatic, hematogenous, or contiguous spread of M. tuberculosis to the skin from an internal focus leading to the de- velopment of LV, scrofuloderma, TB cutis orificialis, miliary TB, and metastatic TB abscesses. Tuberculids are another form of CTB resulting from a hypersensitivity reaction to an internal source of M. tuberculosis antigens. Diagnosis can be made based on history, morphologic features, and histopathologic characteristics but can be complicated and substan- tially delayed because of the resemblance to other dermatologic condi- tions. Furthermore, skin biopsy and/or acid-fast bacilli staining and culture may fail to reveal the presence of M. tuberculosis .A s with TB of other organs, treatment of CTB requires a 4-drug chemotherapeutic regimen that usually consists of rifampin, isoniazid, pyrazinamide, and etham- butol for 2 months followed by a 2-drug regimen for 4 months. De- pending on the type of CTB, several years of chemotherapy and/or surgical excision may be needed.