Undifferentiated spondyloarthropathy in Chinese patients

Background. Undifferentiated spondyloarthropathy (USpA) is a unique group in spondyloarthropathy (SpA). This study will investigate the clinical and laboratory characteristics of USpA in the Chinese population. Methods. Forty two patients with USpA were enrolled from our rheumatology outpatient facility in this retrospective study. SpA was diagnosed according to the European Spondyloarthropathy Study Group (ESSG) criteria. Patients were considered having USpA when they had SpA but did not meet the criteria for the diagnosis of ankylosing spondylitis (AS), Reiter's syndrome or reactive arthritis (ReA), psoriatic arthritis (PsA), and inflammatory bowel diseases (IBD)-related arthritis, etc. Laboratory tests included erythrocyte sedimentation rate (ESR), serum C-reactive protein (CRP), immunoglobulin A (IgA), and human leukocyte antigen B27 (HLA-B27). Results. Among the 42 USpA patients, the ratio of men to women was 1.47:1, and the age at onset was 32.33 ± 10.83 years old. Approximately 61.9% of patients had peripheral arthritis, 30.95% had uveitis, and 64.29% had positive HLA-B27. Among these female USpA patients, compared to males, there is a trend of older age at disease onset, higher percentage of HLA-B27 positive, more peripheral arthritis and uveitis, longer disease duration, and higher level of ESR, and IgA and CRP in serum. The items reaching significant difference between males and females were longer disease duration (p <0.001), higher level of ESR (p <0.001), and serum IgA (p = 0.03). There was no significant difference in clinical and laboratory characteristics between HLA-B27-positive and -negative groups. Conclusions. Studies on USpA patients have not been reported in the Chinese population. In this study, we demonstrate the unique demographic characteristics, clinical and laboratory data of USpA in the Chinese population. These findings should be confirmed by analyzing larger number of patients and longer time for further follow-up. Such studies are crucial to understand the pathogenesis of USpA and evaluate its prognosis.