AdDRESSing T-cell responses to antituberculous drugs

In this issue of the BJD, Ye et al.1 present data on T-cell-specific responses in patients with antituberculosis drug (ATD)-induced maculopapular exanthema (MPE) and drug reaction with eosinophilia and systemic symptoms (DRESS). Understanding these responses helps further our knowledge of the immunopathogenesis of antituberculous hypersensitivity, and ideally it would be translated into diagnostic tests that improve ATD drug safety and guide therapy. Isoniazid, rifampicin, pyrazinamide and ethambutol are the first-line therapy used in the first 2 months to treat tuberculosis (TB) and multiple medications make the identification of culprit drugs difficult in the clear diagnosis of adverse drug reactions (ADRs). This uncertainty has detrimental effects, including interruption of treatment for prolonged periods, systemic corticosteroid use and alternative treatment with less effective regimens.2 To confirm the diagnosis of suspected immunologically-mediated ADRs associated with ATD therapy, a combination of skin tests (prick and intradermal dilutional testing) and patch testing is most often employed in the clinic. However, the specificity and sensitivity of patch testing is dependent on both the host and the offending drug and few validation studies exist. In the cases presented by Ye et al.1 patch testing is shown to be of little utility in DRESS and is unsuitable for cases of MPE; however, the oral provocation test and lymphocyte transformation test show a stronger correlation and support multiple drug reactivity.