Clinical assessment of sacroiliitis and HLA-B27 are poor predictors of sacroiliitis diagnosed by magnetic resonance imaging in psoriatic arthritis

Objective. To determine the frequency and clinical predictors of sacroiliitis diagnosed by magnetic resonance imaging (MRI) in a psoriatic arthritis (PsA) population. Methods. The studied comprised 103 patients with PsA. A careful clinical assessment for sacroiliitis was made from history and examination, and HLA-B27 testing was performed. Sixty-eight patients underwent tilted coronal fat-saturated T-1-weighted and STIR MRI of the sacroiliac joints. Results. Clinical features of moderate or severe sacroiliitis were found in 24/68 (35%) patients. MRI features of sacroiliitis were found in 26/68 (38%) patients. Clinical features of sacroiliitis were present in 14/42 (33%) with normal MRI scans and 10/26 (38%) with abnormal scans (normal vs abnormal scans, P = 0.7). The presence of sacroiliitis on MRI was associated with restricted spinal movements (P = 0.004) and the duration of PsA (P = 0.04). There was no correlation between HLA-B27 and sacroiliitis diagnosed by MRI. Conclusion. Sacroiliitis diagnosed by MRI occurs commonly in PsA but is difficult to detect clinically.