Cutaneous paradoxical inflammatory reaction of erythema induratum of Bazin to standard antituberculosis treatment

IntroductionCutaneous tuberculosis (TBC) is a skin infection due most often to Mycobacterium tuberculosis, an acid-and alcohol-fast bacillus, and rarely due to M. bovis and bacillus Calmette-Gurin (BCG).Cutaneous TBC is rather rare, making up 1.5% to 3% of all extrapulmonary TBC cases (1, 2).It has diverse clinical presentations relative to host immunity and the number of bacilli present in the tissue.Direct inoculation of M. tuberculosis from an exogenous source can lead to tuberculous chancre, TBC verrucosa cutis, and occasionally lupus vulgaris.The endogenous infection may manifest as scrofuloderma, acute miliary TBC, tuberculous gummas, orificial TBC, and lupus vulgaris (1, 2).A separate group of lesions, termed tuberculids, arise due to delayed hypersensitivity reactions to M. tuberculosis or its antigens in individuals with strong cell-mediated immunity.The diagnostic criteria include tuberculoid granuloma (or other suggestive microscopic features) on histopathology, strongly positive Mantoux or interferon-gamma release assay, absence of mycobacteria in the skin and culture, and resolution of skin lesions with antituberculosis therapy (1-4).Mycobacterial DNA can usually be identified with the use of polymerase chain reaction (PCR), proving its causal role.However, failure to detect M. tuberculosis by PCR does not exclude the diagnosis of tuberculids.Among tuberculids, erythema induratum of Bazin (EIB) presents as ulcerative tender, erythematous nodules that are usually confined to the posterior aspects of the calves, although the lesions may affect the lateral and anterior surfaces as well (1,3,4), and it has a female predominance.In cases with negative TBC findings (chest radiograph, tuberculin