Identification and characteristics of patients with axial psoriatic arthritis: clinical, phenotypic and imaging associations.

OBJECTIVE

To present the clinical and imaging characteristics of patients with axial psoriatic arthritis (PsA) and to identify possible subtypes.

METHODS

Data were retrieved from the Greek-multicentre PsA study. Axial PsA (axPsA) was defined as PsA (CASPAR criteria) accompanied by inflammatory back pain (present or ever) and positive imaging findings of the sacroiliac joints and/or spine (MRI: active inflammation of sacroiliac joints and/or spine; X-rays: 1984 New York criteria for radiographic sacroiliitis and/or presence of syndesmophytes in the spine). Demographic and clinical characteristics were compared between axPsA and non-axPsA subsets. Two additional analyses were conducted: (i) isolated sacroiliac joint involvement (sacroiliac axPsA) vs isolated involvement of the rest of the spine (spinal axPsA); (ii) non-radiographic axPsA (nr-axPsA, positive MRI findings only) vs radiographic axPsA (r-axPsA, positive X-ray findings).

RESULTS

Among 922 patients with PsA, 238 (25.8%) had axPsA. Patients with axPsA had less frequently peripheral arthritis at diagnosis, whereas they had increased rates of HLA-B27 positivity, enthesitis ever and inflammatory bowel disease. Among patients with axPsA, 42% (n = 101) had isolated sacroiliac axPsA and 32% (n = 75) had isolated spinal axPsA. Sacroiliac axPsA was associated with younger age (OR: 0.97, 95% CI: 0.94-0.99) and enthesitis at diagnosis (OR: 3.37, 95% CI: 1.66-6.82). A total of 35% of patients with axPsA had nr-axPsA and were more commonly females (OR: 2.59, 95% CI: 1.39-4.82) and younger (OR: 0.96, 95% CI: 0.94-0.99) compared with those with r-axPsA.

CONCLUSION

Approximately one-quarter of patients with PsA exhibit axial involvement, and among them, ∼30% have isolated spinal axPsA and nr-axPsA, respectively.