Application of IFN-gamma releasing assay for the diagnosis of erythema induratum of Bazin

Background Erythema induratum of Bazin (EIB) is regarded to be a hypersensitive reaction to the concomitant tuberculosis. Recently, interferon- releasing assay (IGRA) has been focused as a promising tool in the diagnosis of latent tuberculosis. However, there has been no large scale study to investigate the usefulness of IGRA in the diagnosis of EIB. Objectives To evaluate the diagnostic performance for the detection of EIB. Methods We retrospectively reviewed medical records of all patients with EIB, in the Department of Dermatology, at the Seoul National University Hospital, between April 2009 and September 2011. We analysed clinicopathological features, responses to IGRA and the treatment courses. In addition, we compared positive rate of IGRA in patients with other diseases during the same period. Results All of the 22 patients demonstrated a positive response to IGRA (100%) and showed a good response to anti-tuberculosis treatment. In contrast, positive rate was 63.64% and 66.67% in patients with psoriasis and other vasculitis respectively. We observed complete resolution of skin lesions in 14 patients. Partial resolution was attained in one patient and the other seven patients are currently on the medication and are showing good responses. Conclusion We verified that IGRA has an excellent diagnostic performance in EIB, through this observational study. It is strongly suggested that if EIB is clinicopathologically suspected, IGRA should be performed.