title: Erythema induratum: case series illustrating the utility of the interferon-γ release assay in determining the association with tuberculosis.
abstract: BACKGROUND
  The interferon-γ 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-Guérin (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.
  
  
  OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.forename: Vimal
authors.initials: V
authors.lastname: Prajapati
authors.forename: McKay
authors.initials: M
authors.lastname: Steed
authors.forename: Parbeer
authors.initials: P
authors.lastname: Grewal
authors.forename: Muhammad N
authors.initials: MN
authors.lastname: Mahmood
authors.forename: Geetika
authors.initials: G
authors.lastname: Verma
authors.forename: Alain
authors.initials: A
authors.lastname: Brassard
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D004797:Enzyme-Linked Immunosorbent Assay; D004891:Erythema Induratum / Q000175:diagnosis* / Q000378:metabolism; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D059425:Interferon-gamma Release Tests / Q000379:methods*; D012189:Retrospective Studies; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis*
chemical_list: D007371:Interferon-gamma