Background The frequency of axial disease in Psoriatic Arthritis (PsA) is around 24–78% with additional patients with subclinical disease who have spondylitic changes or sacroiliitis in the absence of clinical findings. Despite that most of the physicians do not perform routine imaging with the argument that subclinical disease has no effects on management decisions.

Objectives We aimed to explore barriers for diagnosing axial disease in PsA and its implications in real life.

Methods PsART (Psoriatic Arthritis Registry of Turkey) is a prospective, multicentre registry where PsA patients are consecutively recruited. Radiographs of the spine and sacroiliac joints were scored by one central reader, whenever available. Patients with axial disease according to the physician were compared with patients with imaging findings only and risk factors for being underdiagnosed were investigated.

Results Among 1195 patients, 35% had axial disease according to the physician who were more frequently men (41.2% vs 32.2%; p=0.04), younger (44.4 (12.2) vs 47.9 (13); p<0.001), more frequently smokers (44.6% vs 34.1%; p<0.001), more on anti TNFs (37.1% vs 29.4%; p=0.01) and had more nail involvement (49.9% vs 43.2%; p=0.03). Within the IBP criteria, the ASAS criteria had the lowest sensitivity (59.7%) which was even lower in women (53.1%). Forty-nine (15.7%) patients were classified as having axial disease according to the rheumatologist despite not fulfilling any of the IBP criteria which was more frequent for women (21.1%) than men (8.2%, p=0.002). Among 71 patients that had syndesmophytes, 20 patients (28.2%) were not classified as having axial disease according to the physician. This was higher for women (15/42, 35.7%) then men (5/29, 17.2%).

There were 126 patients who had sacroiliitis fulfilling the ASAS criteria, despite not being categorized as having axial disease by the clinician. The risk of being underdiagnosed was higher for women (30.8% vs 18.4%; p=0.003). These patients had higher Leeds enthesitis scores, tender and swollen joint counts (table) and were less using anti-TNF medications (14.6% vs 38.7%; p<0.001). The PROs and the physician global assessment were similar, suggesting a similar disease activity state according to the patients and physicians in diagnosed and underdiagnosed groups.

Conclusions Underdiagnosed axial disease is frequent in PsA, women having higher risk and IBP criteria being less sensitive in women. More complex patients (eg with higher enthesitis and peripheral arthritis) have a higher risk of being underdiagnosed. These patients are less frequently treated with biologic treatments, which could be the right treatment choice if were diagnosed. Axial disease needs to be ruled out using imaging modalities, even if back pain does not clinically suggest an inflammatory pattern.

Disclosure of Interest None declared