Should antituberculosis treatment be prescribed in erythema induratum? A case-control and incidence correlation study in Taiwan, 2001-2020.

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Erythema induratum (EI) is a tuberculid associated with Mycobacterium tuberculosis infection. Using polymerase chain reaction (PCR), M. tuberculosis has been identified in Taiwan with a high percentage of EI. However, this pathogen is now rarely detected in Taiwan. To explore the association between EI, the annual incidence of tuberculosis (TB) in Taiwan and treatment outcomes over the last two decades. Patients diagnosed with EI between 2001 and 2020 were enrolled based on histopathology, tissue culture and positive M. tuberculosis PCR tests. Other cases of panniculitis with positive M. tuberculosis PCR results were used as controls. The clinical information of participants was obtained. The results were correlated with the annual incidence of TB and compared between groups. Fifty-five biopsy specimens from patients with EI met the inclusion criteria; three (5%) had positive M. tuberculosis PCR results. One patient diagnosed with erythema nodosum in the control group had a positive M. tuberculosis PCR (n = 1/27; 4%). There was no significant relationship between M. tuberculosis and EI (odds ratio 1.5, 95% confidence interval -0.964 to 3.964). The correlation between the incidence of M. tuberculosis and the number of EI cases was not statistically significant (r = -0.185, P = 0.45). Only four patients received anti-TB treatment; they all showed clinical improvement without recurrence. One patient with M. tuberculosis PCR-positive EI was not treated with anti-TB therapy; however, the skin lesion improved after 3 months. No other patients in the EI group were diagnosed with M. tuberculosis infection over a follow-up period of 508 person-years. Most cases of EI in Taiwan are nodular vasculitis and not tuberculid, owing to well-controlled TB. This condition can be alleviated without anti-TB treatment.