Objectives The aim of our research was to investigate potential etiological factors of undifferentiated spondyloarthritis (uSpA) in comparison with the data obtained in patients with “classic” ankylosing spondylitis (AS).

Methods The study involved 80 patients with spondyloarthritis admitted for the treatment to the Belorussian Republican Centre of Rheumatology (RCR). 40 patients had uSpA (33 males, 7 females; group I). 40 patients had axial AS (39 males, 1 female; group II). uSpA diagnosis before admission to RCR was established on the basis of the lack of compliance with the criteria of other forms of spondyloarthritis, AS diagnosis was based on matching the modified New York criteria of ankylosing spondylitis (1984). The average duration of the disease was 7.6 years and 7.4 months in patients with AS and undifferentiated spondyloarthritis, respectively. Before the admission to RCR infections caused by Chlamydia trachomatis, Yersinia spp., and other intestinal pathogens were excluded in all patients using indirect enzyme-linked immunosorbent assay (ELISA). Still, assuming infections as possible etiology of disease in patients with uSpA all patients in this group were screened for the C. trachomatis infection using polymerase chain reaction (PCR) and/or McCoy cell culture. Specimens for the assay were urethral scraping in males and endocervical scraping in females. Control group of patients with AS was also screened for C. trachomatis infection using the same assays.

Results According to the results of the study, C. trachomatis was detected in 29 (72.5%) of 40 patients with uSpA and only 5 (12.5%) of 40 patients with AS. The difference was statistically significant (p<0.001). In additional 2 (5%) of 40 uSpA patients without C. trachomatis infection during the 1-year follow-up period psoriatic skin plaques were newly diagnosed. After one year of observation only 9 (12.5%) still fulfilled diagnosis of undifferentiated Spondyloarthritis.

Conclusions Thus, diagnosis of chlamydia-induced spondyloarthritis was established in 72.5% of 40 patients with undifferentiated spondyloarthritis, 5% of patients with uSpA were diagnosed with psoriatic spondyloarthritis with musculoskeletal involvement preceding cutaneous lesions and only 12.5% remained with uSpA diagnosis after a 1-year follow-up period. Due to the use of relative insensitive laboratory assays of persistent C. trachomatis detection (ELISA) chlamydia-induces spondyloarthritis often remains undiagnosed. According to our data, the detection of chlamydial infection in patients with undifferentiated spondyloarthritis using PCR and/or McCoy cell culture assays is not just a concomitant finding, but is associated with the etiology of the disease, as in patients with “classic” AS chlamydial infection was detected significantly less often. We believe that timely establishment of chlamydia-induced spondyloarthritis should not be limited by ELISA. Most patients with persistent C. trachomatis infection do not have diagnostically significant serum antibody levels. PCR is a preferable assay for the chlamydial infection detection.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.3787