Whole-body Magnetic Resonance Imaging in Psoriatic Arthritis, Rheumatoid Arthritis, and Healthy Controls: Interscan, Intrareader, and Interreader Agreement and Distribution of Lesions.

Objective: Whole-body MRI (WBMRI) is a promising technique for monitoring patients' global disease activity in inflammatory joint diseases. The validation of WBMRI is limited; no studies have evaluated the test-retest agreement (interscan agreement) and only a few have assessed the intra- and interreader agreement. Therefore, we first examined the interscan agreement of WBMRI in patients with psoriatic arthritis (PsA), rheumatoid arthritis (RA), and healthy controls (HC); and second, we evaluated the intra- and interreader agreement and agreement with conventional hand MRI and determined the distribution of lesions.

Methods: WBMRI was performed twice at a 1-week interval in 14 patients with PsA, 10 with RA, and 16 HC. Images were anonymized and read in pairs with unknown chronological order by experienced readers according to the Outcome Measures in Rheumatology (OMERACT) WBMRI, Canada-Denmark MRI, and the RA MRI scoring system (RAMRIS) and the PsA MRI scoring system (PsAMRIS). Ten image sets were reanonymized for assessment of intra- and interreader agreement. Agreement was calculated on lesion level by percentage exact agreement (PEA) and Cohen κ, and for sum scores by absolute agreement, single-measure intraclass correlation coefficient (ICC).

Results: WBMRI of the spine and peripheral joints and entheses generally showed moderate to almost perfect interscan agreement with PEA ranging from 95% to 100%, κ 0.71-1.00, and ICC 0.95 to 1.00. Intra- and interreader data generally showed moderate to almost perfect agreement. Agreement with conventional MRI varied. More lesions were found in patients than in HC.

Conclusion: WBMRI showed good interscan agreement, implying that repositioning of the patient between examinations does not markedly affect scoring of lesions. Intra- and interreader agreement were moderate to almost perfect.