Background/Purpose: Patients with rheumatoid arthritis (RA) are at a well-documented increased risk of tuberculosis (TB) compared to the general population, both with and without treatment with tumor necrosis factor inhibitors (TNFi). Whether or to what extent these increased risks apply also to patients with ankylosing spondylitis (AS), psoriatic arthritis (PsA), or other types of spondyloarthropathies (SpA), whose age, gender and disease characteristics differ from RA, is much less known. We therefore investigated TB risks in these conditions, in relation to biological treatment and risks in the general population.

Methods: Through linkages including the Swedish national Patient, Population, TB and Rheumatology registers, we identified all individuals in Sweden registered with AS, PsA or SpA, and matched general population comparators, who were followed for TB from 2002 through 2013. Incidence rates were estimated for biological-naïve and biological-exposed patients and their comparators. We calculated hazard ratios (HR) and 95% confidence intervals (CI) for the whole period and stratified by calendar period. HRs were adjusted for age, sex and country of birth.

Results: 38,702 patients with AS, PsA or SpA, and 200,417 population comparators were included. Thirteen percent of patients used a biological drug during the study period, of which 99% was a TNFi. The average age of patients was approximately 10 years lower than the RA patients of the previous study. During the study period, 11 TB cases were identified among the patients, corresponding to an incidence rate (per 100,000) of 2.7 (95% CI 1.3 to 5.6) for biological-naïve patients, 22 (95%CI 8.3 to 59.2) for biological-exposed patients, and 2.4 (95% CI 1.8 to 3.3) for the general population. The HR comparing biological-naïve to biological-exposed patients was 7.5 (95% CI 1.9 to 29), and 1.2 (95% CI 0.5 to 2.7) comparing biological-naïve patients compared to the general population.

Conclusion: Biological-naïve AS, PsA and SpA patients have a similar risk of TB as the general population, and hence lower incidences than those previously reported in RA. However, these patients had a 7.5-fold higher risk of TB when treated with TNFi. Although the absolute risk of TB is low, and the most cases occurred in the biological-naïve group, the risk of TB increased after treatment with TNFi. Table: Incidence rates and 95% confidence intervals of tuberculosis (TB) in the general population and patients with AS, PsA or SpA with and without biologic therapy. Hazard ratios for TB comparing biological-naïve to biological-exposed, overall and stratified by calendar time of follow-up.