How do axial spondyloarthritis subtypes differ in multiethnic Asian population?
Patients with the radiographic axial spondyloarthritis (axSpA) subtype, known as ankylosing spondylitis (AS), are more likely to be positive for human leukocyte antigen (HLA)-B27, hypertensive, and have uveitis and poorer spinal mobility, whereas those with the nonradiographic subtype (nr-axSpA) are more prone to experience poorer well-being and quality of life (QoL), according to data from a multiethnic Asian population in Singapore.
The population comprised 262 axSpA patients (mean age at diagnosis, 31.7 years; 79 percent male; 82 percent Chinese), among whom 215 had AS and 47 had nr-axSpA. [Int J Rheum Dis 2019;doi:10.1111/1756-185X.13603]
Compared with those who had the nonradiographic subtype, patients with AS were older (mean age, 42.7 vs 37.4 years; p=0.02), had longer disease duration (mean, 10.9 vs 6.4 years; p<0.01) and higher Bath Ankylosing Spondylitis Metrology Index (mean, 3.1 vs 1.5; p<0.01), and tended to be HLA‐B27 positive (82 percent vs 68 percent; p=0.03), hypertensive (17 percent vs 0 percent; p<0.01) and associated with uveitis (33 percent vs 17 percent; p=0.03).
In contrast, nr‐axSpA patients had higher scores for Bath Ankylosing Spondylitis Global (BAS-G; mean, 46.9 vs 38.6; p<0.01), Bath Ankylosing Spondylitis Disease Activity Index (mean, 4.2 vs 3.5; p=0.02) and ASQoL (mean, 4.9 vs 3.5; p=0.04) at baseline.
There were no significant between-group differences in patient global assessment, Bath Ankylosing Spondylitis Functional Index (BASFI), AS Disease Activity Score – C‐reactive protein (CRP), Health Assessment Questionnaire (HAQ), Short‐Form 36 (SF-36) physical and mental component summary, as well as in medications used and mean erythrocyte sedimentation rate and CRP.
“It has been presumed that nr‐axSpA is an early form of axSpA and possibly a milder form of disease…However, despite our patients with nr‐axSpA having similar levels of disease activity and better spinal mobility compared to patients with AS, they had poorer QoL based on ASQoL indices, and experienced greater effect of the disease on their well‐being as reflected by poorer BAS‐G scores,” the investigators noted.
They also pointed out that the lack of differences in other patient-reported outcome measures (eg, BASFI, HAQ and SF‐36) and inflammatory markers (eg, ESR and CRP) between the two patient groups suggest that nr‐axSpA is far from being a milder form of AS.
Another important thing to note is the similarity in the proportion of patients on biologic disease-modifying antirheumatic drug between the AS and nr‐axSpA groups. “This finding indicates that physicians may be treating patients with AS and nr‐axSpA similarly, regardless of the presence or absence of radiographic sacroiliitis,” the investigators said.
In light of the present data, “it would be important to be more vigilant in screening for uveitis and cardiovascular risk factors in our multiethnic Asian cohort of AS patients and to explore why nr‐axSpA patients are experiencing more pain and fatigue,” they added.