Erythema Induratum: Case Series Illustrating the Utility of the Interferon-γ Release Assay in Determining the Association with Tuberculosis

Background: The interferon- release assay (IGRA) is a novel method for detecting previous sensitization to tuberculosis (TB). Despite having several advantages over the tuberculin skin test (TST), including higher specificity and no influence from past bacille Calmette-Guerin (BCG) exposure, there are a limited number of reports describing its application in patients with erythema induratum (EI)/nodular vasculitis (NV), which is usually but not always related to TB. Objectives: The aim of our case series was to evaluate the usefulness of the IGRA for determining a TB association in patients with EI/NV. Methods: Retrospective chart reviews were conducted on four patients diagnosed with EI/NV at our institution in whom an IGRA had been performed. Results: All four subjects had positive TST results. The IGRA was also positive and therefore supported a link with TB in two cases. One patient responded completely to anti-TB therapy, whereas the second was lost to follow-up. Both cases unrelated to TB, by virtue of negative IGRAs, demonstrated complete response to immunosuppressive therapy (methotrexate), with one individual having failed anti-TB therapy first. Conclusion: Our case series highlights the utility of the IGRA for establishing a TB association in patients with EI/NV. Although limited by a small sample size, we propose adjunctive use of this test at the time of EI/NV diagnosis, especially in the setting of previous BCG exposure, so that management can be tailored according to whether an underlying relationship with TB exists. Contexte: Le test de liberation d'interferon gamma (TLIG) est un nouvel examen de detection de sensibilisation anterieure a la tuberculose (TB). Malgre plusieurs avantages comparativement au test cutane a la tuberculine (TCT), y compris sa plus grande specificite et l'absence d'influence resultant d'une exposition anterieure au bacille de Calmette et Guerin (BCG), il existe un petit nombre de rapports faisant etat de son application chez des patients presentant un erytheme indure (EI), ou une vascularite nodulaire (VN), une affection qui est generalement, mais pas toujours, liee a la TB. Objectif: La serie de cas visait a evaluer l'utilite du TLIG dans la determination d'un lien avec la TB chez des patients presentant un EI, ou une VN. Methode: Nous avons procede a un examen retrospectif des dossiers de quatre patients chez qui un diagnostic d'EI, ou de VN, avait ete pose dans notre etablissement et qui avaient subi le TLIG. Resultats: Les quatre malades avaient obtenu des resultats positifs au TCT. Le TLIG s'est egalement revele positif et, de ce fait, confirmait l'existence d'un lien avec la TB chez deux d'entre eux: l'un a parfaitement reagi au traitement antituberculeux, tandis que la trace du second a ete perdue au cours du suivi. Quant aux deux autres cas non lies a la TB, en raison des resultats negatifs du TLIG, ils ont parfaitement reagi au traitement immunosuppresseur (methotrexate), et ce, malgre l'echec d'un traitement antituberculeux anterieur chez l'un des patients.