Prevalence of latent tuberculosis infection in patients with moderate to severe psoriasis taking biologic therapies in a dermatologic private practice in Miami, Florida

BackgroundThe reactivation of a latent tuberculosis infection is one of the possible major events that may occur during biologic therapies for inflammatory chronic diseases such as psoriasis. Although its main screening test is regularly used in clinical practice, there are few studies about the prevalence of this silent mycobacterial infection and the rate of positive convertors during treatment. ObjectiveTo assess the prevalence of latent tuberculosis infection (LTBI) in patients with moderate to severe psoriasis receiving biologic therapy by using tuberculin skin test as a screening method and to evaluate the rate of conversion of tuberculin skin test (TST) during the treatment with biologics. MethodsA total of 445 patients were included in our retrospective study, conducted from January 2006 to September 2012. Tuberculin skin test was performed in all patients prior to treatment and once a year during the follow-up. PPD was considered positive with an induration above 5mm, following the recommendations of Centers for Disease Control and Prevention/ America Thoracic Society. Data analysis was obtained with SPSS 20.0. ResultsThe prevalence of LTBI in our population before initiating the treatment was 4.5% by using TST screening method. During the treatment, 10 cases that were initially TST-negative became positive. Only one of the patients developed active tuberculosis infection. The other 9 TST-positive patients were detected during the regular annual screening, and no symptoms or findings on chest x-ray were seen. All the patients were treated with isoniazid (INH) for ninemonths, and biologic therapy was restarted after onemonth of treatment with INH without development of overt TB infection in any of them during the follow-up period of the study. The mean time to becoming TST positive from start date was 26.7months (range from 8months to 5years). As the PPD was done annually, it is unknown exactly when the patients became TST positive. Prior to initiating treatment, 20 patients were found to be TST positive. All patients had clear chest x-rays and were treated with ninemonths of INH prior to initiating biologic therapy at least month later. ConclusionsThe use of a screening tool for LTBI is mandatory in patients taking biologic therapies to avoid severe infectious complications. Periodic follow-up is also crucial as positive results may be seen after prolonged use of these agents.