How many patients with rheumatic diseases and TNF inhibitors treatment have latent tuberculosis?

OBJECTIVES Spanish clinical guidelines recommend screening patients for tuberculosis (TB) before TNF inhibitors (TNFi) treatment. Our objective was to estimate the prevalence of TST seroconversion as an estimation of the prevalence of latent TB in patients with rheumatic diseases and TNFi treatment that have already been screened for tuberculosis. METHODS TST, booster and chest x-ray were performed to patients with rheumatic diseases, TNFi treatment, negative tuberculin skin tests before treatment and that were attending the rheumatology Department of three different hospitals in Barcelona. According to the Spanish Society Rheumatology guidelines, these patients had not received TB prophylaxis treatment. RESULTS One hundred and forty patients were included in the study. The tuberculin skin test was positive in 4.28% (n=6) of the patients. 50% of the patients were undergoing TNFi ≤ 2 years, being two of the patients only one year on the TNFi when a positive TST was detected. This shows that a conversion of the TST can occur even few months or years after the TNFi is started. CONCLUSIONS The present study observed that 4.28% of patients with rheumatic diseases on TNFi who did not have performed a pre-treatment TB prophylaxis, had a conversion of the TST. Moreover, the conversion of the TST had been within the first two years of treatment in half of the patients of our cohort. In spite of these results, false TST positives in the diagnosis of latent TB cannot be excluded as an explanation for our results.