Background/Purpose:

There is limited evidence on the phenotypic characteristics of axial spondyloarthritis (axSpA) patients (pts) in various geographic regions around the world. This analysis aimed to compare demographic and disease-related characteristics in axSpA pts included in PROOF study in different regions.

Methods:

PROOF is an ongoing 5-year prospective observational study in pts with recently (≤1year prior to study enrollment) diagnosed axSpA and fulfilling the ASAS classification criteria. Baseline data of pts with centrally confirmed sub-classification as non-radiographic (nr)-axSpA or radiographic (r)-axSpA, based on the absence or presence of definite radiographic sacroiliitis (≥grade 2 bilaterally or ≥grade 3 unilaterally), were considered in the current analyses. Twenty-nine participating countries were divided into 4 geographic regions: 1. Europe and Canada (EC), 2. Middle East and South Africa (MEA), 3. Asia (China only), and 4. Latin America (LA).

Results:

A total of 1583 axSpA pts were centrally sub-classified as nr‑axSpA (n=544) or r-axSpA (n=1039). The proportion of patients with r-axSpA was highest in China (81%), followed by MEA (64%), EC (61%) and LA (54%) (Table). Gender distributions were similar across the regions in nr‑axSpA (M:49% vs. F:51%), while in r-axSpA the proportions of men differed, with the highest in China (79%) and lowest in MEA (58%). In both nr-axSpA and r-axSpA, Chinese patients were the youngest, reported the shortest time since chronic back pain onset and had the highest HLA-B27 prevalence. The frequency of peripheral manifestations did not differ between nr-axSpA and r-axSpA within the regions, however significant differences were observed in the frequency between the regions: peripheral arthritis was most common in LA (>50% pts); enthesitis in LA and MEA regions (≈50%), while dactylitis was not frequent with the highest prevalence again in LA (≈12%). Similarly, the prevalence of Extra-articular manifestations (EAMs) also did not differ between nr-axSpA and r-axSpA patients within the regions. Uveitis was significantly more frequent in r-axSpA pts in LA (19%) and EC (≈12%) vs China (6%). Psoriasis was almost absent in China, and had the highest frequency in EC and LA (≈10%). There were no IBD cases reported in China, while the highest IBD prevalence was reported in EC (3 and 6% for r-axSpA and nr-axSpA, respectively). Use of NSAIDs did not differ between regions, but there were differences in the frequency of therapy with conventional DMARDs, glucocorticoids and TNF inhibitors.

Conclusion:

The results showed differences between axSpA phenotypes between the geographic regions: peripheral manifestations were more prevalent in LA and MEA. EAMs were least frequent in Asian (Chinese) pts who were also the youngest, had the lowest disease activity and impairment in physical function.