Background/Purpose: Psoriatic arthritis mutilans (PsAM) is the most severe form of Psoriatic arthritis (PsA). Research on PsAM has been hampered by the lack of an accepted disease definition and a consensus on radiographic assessment. We recently performed a systematic review of the literature and conducted a survey of members of the Group for Research and Assessment of Psoriasis and PsA (GRAPPA) to identify radiographic features associated with PsAM. Based on the results of these studies, joint erosion of the entire articular surfaces on both sides of the joint, bone resorption leading to bone shortening, pencil-in-cup deformity, ankylosis, and subluxation were deemed to be PsAM manifestations. Thus, the aim of this study was to determine the reliability of assessing PsAM features on plain radiographs. 

Methods: The radiographs of 35 PsA patients who have one of the five features in at least one joint of the hands or feet were retrieved and duplicated to generate 70 sets of images. Three rheumatologists, blinded to diagnosis, independently evaluated the radiographs for the five PsAM features in random order. A total of 42 joints, including wrists, all joints of the hand, all metatarsophalangeal joints and the interphalangeal joints of the first toes, were evaluated for each set of images. Inter- and Intra-observer reliability of the five features (joint erosion of the entire articular surfaces on both sides, bone resorption, pencil-in-cup change, ankylosis, and subluxation) in each joint were determined using the kappa statistic with standard errors calculated to accommodate an association between joints within patients. 

Results: Moderate inter-rater agreement was observed for radiographic assessment of PsAM when the five PsAM features were considered as separate categories (kappa 0.63). The kappa improved to 0.83 when the PsAM features were grouped together as one category, indicating excellent inter-rater reliability in identifying severe joint damage. However, the specific agreement for each of the five PsAM features ranged from poor to moderate. Specifically, the assessment of joint erosion involving entire articular surfaces on both sides of the joint and bone resorption showed a kappa of 0.22 and 0.17, respectively whereas pencil-in-cup change, ankylosis and subluxation showed a kappa of 0.59, 0.76 and 0.52, respectively. Intra-rater reliability is excellent with an overall kappa ranging from 0.81 – 0.83. Based on these results, a revised evaluation protocol, where subluxation was removed and bone resorption and joint erosion were combined into one category as severe osteolysis, was applied to the analysis. The assessment of severe osteolysis showed an improved kappa of 0.54, and the kappa for overall inter-rater agreement in PsAM assessment increased to 0.72 with the revised protocol.

Conclusion: These results indicate that there is moderate agreement in radiographic assessment of severe joint damage associated with PsAM. However, the agreement for specific features such as severe joint erosion and bone resorption was poor. The new definitions of the PsAM features and the revised evaluation protocol showed promising result in improving the feature-specific and overall agreement in radiographic assessment of PsAM.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/reliability-of-radiographic-assessment-of-psoriatic-arthritis-mutilans/