Page 50 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER THREE
peripheral disease in AS, showing an arthritis prevalence of 18-58% (9,11,25–27), an enthesitis prevalence of 34-74% (9,25,26) and a dactylitis prevalence of 6-8% (9,26,28) (all reported at any time during the disease). One study of Vander Cruyssen et al showed higher arthritis- (58%) and enthesitis (50%) prevalence (ever occurrence) (25). A longer mean symptom duration (11 years) and the retrospective reporting in this study may have caused this difference. Importantly, none of the AS studies reported peripheral disease prevalence in AS as the primary outcome of the study.
Our prevalence data of extra-articular disease were also in line with previous data of AS, showing a uveitis prevalence of 22-37% (25–27,29–31), an IBD prevalence of 4-16% (27,30–34), and a psoriasis prevalence of 4-9% (6,27,30,31,33,34), which all adds to the robustness of the aggregated estimates we have provided. The prevalence of uveitis in our study population was lower than the prevalence in the meta-analyses of Stolwijk et al and Zeboulon et al, reporting a pooled prevalence of 25.8% and 32.7%, respectively (29,30). This might be caused by a higher mean disease duration (15.9 years in the meta-analysis of Stolwijk et al and 17.7 years in the meta-analysis of Zeboulon et al). Another explanation for this prevalence difference is that both review studies also included clinical trials, enriched with patients with more active and severe disease.
When we compare AS patients to nr-axSpA patients, HLA-B27 was equally prevalent in nr-axSpA and AS patients. Because HLA-B27 is the main entry requirement for fulfilling the ASAS criteria for nr-axial SpA via the clinical arm, HLA-B27 might be artificially overrepresented in the nr-axSpA arm. However, the Esperanza cohort differentiated axSpA in AS and nr-axSpA in a clinical and imaging arm, enabling us to compare the HLA-B27 prevalence in both arms. No statistically significant difference in HLA-B27 prevalence in the imaging arm of nr-axSpA (where HLA-B27 is not required to fulfill the ASAS criteria) and in AS was shown (58.3% vs. 67.6%, respectively) (44), providing evidence for equal HLA-B27 prevalence in nr-axSpA and AS.
Our data show that AS patients were more frequently male than nr-axSpA patients (prevalence difference 23.2%). These results are in line with previous study results, showing that male patients have more structural damage on radiographs than female axial SpA patients (11,47–49). Because the mNY criteria require sacroiliitis as shown on plain X-ray, channeling of male patients occurs. For nr-axSpA, this channeling does not exist, which is reflected in the equal gender distribution in nr-axSpA.
Interestingly, when we subcategorized the study population in HLA-B27+ and HLA-B27- AS and nr-axSpA patients, the male predominance among AS patients was the same in HLAB27+ and HLAB27- patients, challenging the concept of AS as a HLA-B27+ driven, predominantly male disease.
Our study data show that peripheral and extra-articular disease manifestations are, with the exception of uveitis, frequent and equally prevalent in AS and nr- axSpA. These data further support the idea of axial SpA being one disease
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