Features of Axial Spondyloarthritis in Two Multicenter Cohorts of Patients with Psoriasis, Uveitis, and Colitis Presenting with Undiagnosed Back Pain.

Objective: We aimed to assess: 1. The frequency of axial spondyloarthritis (axSpA) according to extra-articular presentation and HLA-B27 status; 2. Clinical and imaging features that distinguish axSpA from non-axSpA; 3. The impact of MRI on diagnosis and classification of axSpA.

Methods: The Screening in Axial Spondyloarthritis in Psoriasis, Iritis, Colitis, (SASPIC) study enrolled patients in two multicenter cohorts. Consecutive patients with undiagnosed chronic back pain attending dermatology, ophthalmology, and gastroenterology clinics with PsO, AAU, or IBD, were referred to a local rheumatologist with special expertise in axSpA for a structured diagnostic evaluation. The primary outcome was proportion of patients diagnosed with axSpA by final global evaluation.

Results: Frequency of axSpA was 46.7%, 61.6%, and 46.8% in SASPIC-1 cases (n=212) and 23.5%, 57.9%, and 23.3% in SASPIC-2 cases (n=151) with PsO, AAU, or IBD, respectively. Among B27 positives, axSpA was diagnosed in 70%, 74.5%, and 66.7% in SASPIC-1, and in 71.4%, 87.8%, and 55.6% in SASPIC-2 in patients with PsO, AAU, or IBD, respectively. All musculoskeletal clinical features were non-discriminatory. MRI was indicative of axSpA in 60-80% of patients and MRI in all patients (SASPIC-2) versus on-demand (SASPIC-1) led to 25% fewer diagnoses of axSpA in HLA B27 negatives with PsO or IBD. Performance of the ASAS classification criteria was greater with routine MRI (SASPIC-2) though sensitivity was lower than previously reported.

Conclusions: Optimal management of patients presenting with PsO, AAU, IBD, and undiagnosed chronic back pain should include referral to a rheumatologist. Conducting MRI in all patients enhances diagnostic accuracy.