Evaluation of Ankylosing Spondylitis Spinal Mobility Measurements in the Assessment of Spinal Involvement in Psoriatic Arthritis

Objective. To determine the clinical usefulness of spinal mobility measurements used for ankylosing spondylitis (AS) to assess spinal involvement in patients with psoriatic arthritis (PsA). Methods. We assessed 100 patients with PsA and 103 patients with AS. Patients were classified as having axial PsA if they had grade 2 or higher unilateral sacroiliitis in the presence of spinal symptoms. All PsA patients, without taking the degree of joint involvement into consideration, were evaluated using several measurements for AS. Spinal measurements were compared with axial and peripheral forms of PsA, and the ability of the techniques to discriminate between the 2 forms of PsA was analyzed using the Mann-Whitney U test and the area under the receiver operating characteristic (ROC) curve. A logistic regression model was used to determine the best measurements for evaluating axial PsA. Finally, the results of measurements for axial PsA were compared with those for AS. Results. Of the 100 PsA patients, 46 met the classification criteria for axial PsA, which presented more severe spinal measurement assessments compared with peripheral PsA. Modified Schober test, lumbar side flexion, chest expansion, and cervical rotation measurements performed best under the ROC curve. Modified Schober test, lumbar side flexion, and cervical rotation were the more suitable measurements for assessing axial PsA. There were only minor differences between axial PsA and AS. Conclusion. The spinal measurements used to evaluate AS performed well to assess spinal involvement in PsA. These measurements, notably the modified Schober test, lumbar side flexion, and cervical rotation, should be used in daily clinical practice to assess PsA patients with spinal involvement.