Patients With Spondyloarthritis With vs Without Root Joint Disease Have Distinct Clinical Phenotype

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The primary objective of the study was to compare the clinical characteristics of patients with spondyloarthritis with and without root joint disease.

Patients with spondyloarthritis (SpA) with root joint disease (RJD) have a distinct clinical phenotype compared with those without RJD, according to study results published in Rheumatology. In addition, approximately one-thirds of patients with SpA have RJD involving the hip vs shoulder.

Previous studies have shown that peripheral joint involvement may occur in patients with SpA. Data suggest a correlation between root joint involvement, including the hip and shoulder, and a more severe course of the axial involvement and worse spinal mobility.

The current study aimed at comparing the clinical characteristics of patients with SpA with and without RJD.

Using data from the Assessment of Spondyloarthritis International Society Peripheral Involvement in Spondyloarthritis (ASAS-PerSpA), which is a multicenter, international study with patients with SpA from 24 countries, the researchers conducted a post-hoc analysis comparing data from patients with SpA with and without RJD.

Of 4465 patients with SpA, RJD occurred in 1503 patients (33.7%), including hip involvement in 1082 (24.2%), shoulder involvement in 589 (13.2%), and both hip and shoulder involvement in 299 (6.7%) patients.

Patients with vs without RJD were significantly younger at disease onset (mean age, 28.9 vs 30.9 years, respectively; P <.001). The prevalence of RJD was highest in Asia (57.4%) and lowest in Europe and North America. Patients from Asia were younger, had the earliest age at hip or shoulder involvement, and had the shortest diagnostic delay.

The prevalence of bamboo spine, loss of lumbar lordosis, or thoracic kyphosis, was higher among patients with RJD compared with those without RJD. Uveitis (19.2% vs 15.2%, respectively; P =.001) and enthesitis (55.1% vs 39.0%, respectively; P <.001) were also more common among patients with RJD vs without RJD. Among patients with vs without RJD, total joint count (3.4 vs 2.1 joints, respectively; P <.001) and the use of conventional synthetic disease-modifying antirheumatic drugs (csDMARDs; 76.4% vs 62.1%, respectively; P <.001) were higher.

Positive human leukocyte antigen (HLA)-B27 was more common among patients with RJD compared with those without RJD (49.4% vs 44.7%, respectively; P <.001);  multivariable analysis showed a significant association between RJD with a higher prevalence of HLA-B27 positivity, suggesting HLA-B27 might be a genetic risk marker for RJD severity. Although hip involvement was associated with HLA-B27 positivity, there was no significant association between shoulder involvement and HLA-B27 positivity.

Shoulder involvement was associated with older age at onset and features of peripheral disease, including dactylitis, enthesitis, and peripheral tender and swollen joint counts. Shoulder involvement was associated with inflammatory bowel disease and psoriatic arthritis, and was the least common in axial SpA.

The study had several limitations, including the potential misclassification of patients with peripheral SpA because of RJD involvement, the cross-sectional design, and the lack of confirmatory imaging data.

“This is the first and largest observational study to describe the prevalence and the clinical characteristics of both hip and shoulder involvement across a whole spectrum of patients [with SpA]. This worldwide analysis through 4 continents showed that the prevalence of RJD was 33.7% and was mostly driven by the hip involvement, which incited a separated analysis for the hip and for the shoulder involvement,” the researchers concluded.


Ziadé N, El Hajj J, Rassi J, et al. Root joint involvement in spondyloarthritis: a post-hoc analysis from the international ASAS-PerSpA study. Rheumatology (Oxford). Published online April 26, 2021. doi:10.1093/rheumatology/keab380