Approximately half of people diagnosed with axial spondyloarthritis (SpA) according to the Assessment of Spondyloarthritis International Society (ASAS) criteria also displayed signs of peripheral SpA. Patients with axial and peripheral symptoms demonstrated greater disease activity than patients with axial symptoms only, according a report published in RMD Open.
Although patients with SpA may have axial or peripheral symptoms or a combination of both the current ASAS classification system allows for diagnosis as either axial SpA, based on the presence of back pain, or peripheral SpA. The combined manifestations of disease do not have a separate category and therefore are less understood than the separate axial or peripheral presentations. Investigators sought to evaluate the prevalence of axial disease with peripheral features (arthritis, dactylitis or enthesitis) and its effect on overall disease activity.
Between June 2007 and August 2012, a total of 314 patients fulfilled ASAS criteria for SpA and were enrolled in the cross-sectional, observational study. Participants were divided into those with axial SpA (n=230; median age, 41 years; 63% men; median age of onset, 32 years) or peripheral SpA (n=84; median age, 48 years; 58% men; median age of onset, 38 years). There were significant differences between the groups regarding age (P =.005) and age of onset (P =.001).
Disease activity measures included the physician’s global assessment (PGA), the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Ankylosing Spondylitis Disease Activity Score based on C-reactive protein (ASDAS-CRP). At baseline, patients diagnosed with axial SpA had higher activity scores compared with those with peripheral SpA (P <.001 for all), with regard to median PGA (48 vs 31), median BASDAI (4.9 vs 3.0), and median ASDAS-CRP (2.8 vs 2.0).
On further analysis, the axial SpA group was divided into patients with axial SpA only (n=112; median age, 39 years; 63% men; median disease duration, 3.1 years; median age at onset, 32 years) or combined axial SpA with peripheral symptoms (n=118; median age, 44 years; 64% men; median disease duration, 4.6 years; median age at onset, 34 years). In the combined group, arthritis, enthesitis, or dactylitis were present in 63.6% (P ≤.001), 61.9% (P ≤.001) and 7.6% (P =.003) of individuals, respectively. Compared with patients with axial SpA only, the combined group showed significantly higher disease activity on the median PGA (53 vs 44; P =.009), BASDAI (5.4 vs 4.4; P =.001), and ASDAS-CRP (3.0 vs 2.6; P =.014).
Study limitations included a lack of assessment of individual peripheral manifestation effects, inclusion of only patients with axial SpA in the final analysis, which may yield selection bias, and a cross-sectional design that prohibited evaluation of therapeutic effects.
“The data suggest that it remains crucial to assess the overall disease activity and the different domains of the disease, even when classified as axial disease. Treating accordingly may improve outcome,” the authors noted. They recommended that future research involve larger longitudinal studies that focus on peripheral disease influences and long-term outcomes.
de Winter JJ, Paramarta JE, de Jong HM, van de Sande MG, Baeten DL. Peripheral disease contributes significantly to the level of disease activity in axial spondyloarthritis. RMD Open. 2019;5(1):e000802.