Background/Purpose:  Estimates of axial involvement in PsA vary from 25% to 70% depending on the inclusion criteria. Three sets of criteria are available for defining inflammatory back pain (IBP) in Ankylosing Spondylitis (AS): Calin, Rudwaleit and ASAS criteria. We aimed to determine whether these criteria are useful screening tools for axial involvement in PsA and to describe the clinical features in PsA patients with IBP, mechanical back pain (MBP), no Back Pain (BP) and silent BP.

Methods:   Patients with PsA have been followed prospectively at 6-12 month intervals according to a standard protocol since 1978. Radiographs of peripheral joints and spine are performed at 2 year intervals. All data are tracked in a computerized database.  From the database we extracted data at the first visit since 2010 on the presence of back pain, as well as criteria for IBP (Calin, Rudwaleit and ASAS). At each visit a rheumatologist also recorded whether a patient had back pain, and whether it is inflammatory or mechanical based on independent clinical judgement.  We tested the agreement between physician assessment (presence or absence of IBP) and IBP criteria. Patients whose radiographic changes met the New York (NY) Criteria for AS or had any radiographic changes consistent with sacroiliitis and/or syndesmophytes on x-ray and/or MRI were analyzed for the agreement with the presence of any BP, IBP by physician assessment, and fulfilling IBP criteria, using the Kappa coefficient.  MRI was done only if there was a suspicion of axial involvement but the x-rays were negative. Descriptive statistics are provided.

Results:   171 patients were identified from the database. The patients were mostly male (52%), mean age of onset of PsA was 43.3±13.6, and mean age at first PsA clinic visit was 46.6±13.0 years. All patients had radiographic data available at clinic entry. The prevalence for BP was 56.2% (IBP 38.01%; MBP 18.12%). 27 out of 171 (15.79%) patients with baseline x-rays fulfilled the NY radiographic criteria for AS. 45 out of 171 (26.32%) patients had any radiological sacroiliitis and/or syndesmophytes. 9 out of 31 (29.03%) patients with no axial disease on x-ray had evidence of axial disease on MRI. 18 (24.0%) of the patients with no back pain had “silent” BP (evidence of axial disease on radiology (x-ray or MRI)). The agreement (kappa coefficient) between physician assessment and IBP criteria in all patients was highest for the Calin criteria (0.81, 95% CI (0.72, 0.91)), followed by the ASAS criteria (0.72, (0.61, 0.81)), and the Rudwaleit criteria (0.71, (0.59, 0.83)). There was no significant agreement between the presence of radiographic NY criteria and the presence of back pain, physician assessment of IBP, or the IBP criteria. There was also no agreement between physician assessment of IBP and any radiographic change (syndesmophytes or sacroiliitis of at least Grade 2). Mean BASMI, BASDAI, and BASFI were highest in PsA patients with IBP than those with MBP, no BP or “silent” BP.

Conclusion:   Patients with PsA report less back pain than AS patients. The low level of agreement between physician assessment and radiological presence of axial PsA indicates that we should consider axial imaging in all patients with PsA regardless of the presence of the nature of BP.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/back-pain-in-psoriatic-arthritis-defining-prevalence-characteristics-and-performance-of-the-different-inflammatory-back-pain-criteria-in-a-psoriatic-arthritis-cohort/