Anti-nuclear antibody and enthesitis were frequently detected in female patients with undifferentiated peripheral spondyloarthritis in Japan

Abstract Background The clinical features of patients with spondyloarthritis (SpA) differ between women and men. Peripheral lesions of SpA are more common in women than in men. Compared with reports on psoriatic arthritis (PsA), while reports on patients meeting the criteria for peripheral SpA or patients with undifferentiated peripheral SpA (upSpA) are scarce. This study aimed to elucidate the detailed manifestations of upSpA and the sex differences in situations of low human leukocyte antigen B27 positivity.Methods This multi-center observational study was conducted between April 2020 and June 2024. Among 38 patients with SpA, participants with concomitant inflammatory bowel diseases or meeting with either axial SpA, PsA or reactive arthritis (ReA) criteria were excluded. We collected physical findings and laboratory data on 29 cases of upSpA (19 women and 10 men; mean age standard deviation: 41.6 years 16.3 vs. 60.2 years 11.2). We primarily analyzed the data to examine the relationship between sex and clinical findings.Results The rate of tenderness of the epicondyles of humerus were 79.0% in women and 40.0% in men (p = 0.047). The prevalence rate of tenderness of the Achilles tendon was 52.6% in women and 10.0% in men (p = 0.029). These areas in the women had a higher prevalence rate of enthesitis than those in men. Serum C-reactive protein (CRP) positivity in women (21.1%) were lower than in men (80.0%) (p = 0.004). The positive rate of anti-nuclear antibody, which was defined at a dilution of ≥ 1:160, was higher in women (47.4%) than in men (0%) (p = 0.009).Conclusion Women with upSpA frequently experience enthesitis of the epicondyles of humerus and the Achilles tendon, as well as a lower serum CRP positivity and a higher incidence of positive anti-nuclear antibody, compared to men, in Japan.