Although MRI of the sacroiliac joints (SIJ) is the most sensitive imaging modality for early diagnosis of axial spondyloarthritis (axSpA) it is costly and not readily available. Therefore, clinicians still rely primarily on radiography. The relative degree to which radiography and MRI changes diagnostic ascertainment of axSpA in patients presenting with undiagnosed back pain has not been formally studied. We aimed to assess the relative impact of radiography and MRI evaluation on diagnostic ascertainment of axial SpA in patients presenting with undiagnosed back pain to rheumatologists, and the impact of central reading on diagnostic ascertainment.

The multicenter Screening for Axial Spondyloarthritis in Psoriasis, Iritis, and Colitis (SASPIC) Study is aimed at early detection of axial SpA in consecutive patients presenting with undiagnosed back pain. Consecutive patients ≤45 years of age with ≥3 months undiagnosed back pain with any one of psoriasis, acute anterior uveitis (AAU), or colitis undergo routine clinical evaluation by a rheumatologist for axial SpA and MRI evaluation is ordered per rheumatologist decision. The rheumatologist determines the presence or absence of axial SpA and the degree of confidence in the diagnosis (-10 (definitely not SpA) to +10 (definite SpA) on a numerical rating scale) at 3 consecutive stages: 1. After the clinical evaluation; 2. After the results of labs (B27, CRP) and radiography; 3. After the results of MRI evaluation. We assessed diagnostic ascertainment at each step at the categorical level (axial SpA yes/no) and also according to the degree of confidence (mean (SD) confidence). Two central readers assessed radiographs and MRI scans.

234 patients (51.3% male, mean age 34.6 years, mean symptom duration 7.0 years, mean back pain duration 7.1 years, B27+ 36.3%) were referred with AAU (29.9%), psoriasis (18.8%), Crohn’s colitis (32.1%), ulcerative colitis (19.2%). The number of patients diagnosed clinically with axSpA decreased after radiography and then decreased further after MRI while confidence in the diagnosis progressively increased (Table 1). After central reader assessment of imaging, the number of patients diagnosed with axSpA decreased substantially compared to assessment by local readers (Table 2).

In a setting of undiagnosed back pain and higher risk for axial SpA, imaging is primarily helpful in ruling out SpA and reducing false positives. Despite this, central reading of imaging raises concerns regarding ascertainment of false positive SpA in routine practice.

Table 1

Table 2