SAT0349 A novel scoring system to differentiate psoriatic arthritis from nodal osteoarthritis on plain-film radiographs
Authors: R. Mandegaran, E. Nikiphorou, S. Bahadur, C. Hughes, B. Kirkham, A. Zavareh
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Differentiating Psoriatic Arthritis (PsA) and Nodal Osteoarthritis (NOA) in patients with interphalangeal joint (IPJ) involvement is often challenging.<sup>1–3</sup> Yet, the distinction is important to make, especially as the treatment for these conditions is vastly different. Here we present a novel scoring system based on identifying often subtle but characteristic radiographic features of both conditions on bilateral hand plain-film radiographs. <h3>Objectives</h3> To describe the key radiographic discriminating features that underpin a new scoring system aimed primarily to differentiate PsA from NOA. <h3>Methods</h3> The initial scoring methodology was tested through blind analysis and scoring of 99 bilateral hand radiographs of patients with a confirmed clinical diagnosis of PsA, NOA and RA.<sup>4</sup> In this initial study, anonymised radiographs were read by a Musculoskeletal Radiologist blinded to all clinical information. The reader correctly identified the clinical diagnosis in 100% of radiographs. The analysis method was taught to 3 specialist trainees, in a 1 hour training session. They assessed the same radiograph series with an accuracy of 67%–88%. We refined the radiograph analysis method to develop a scoring system by developing weighted scores for different PsA arthropathic features. These include periarticular erosions and new bone formation (NBF), reduced joint space, soft tissue oedema and asymmetry of findings. Osteoarthritis features included marginal osteophytes, subchondral sclerosis/cysts and reduced joint space. <h3>Results</h3> All bilateral interphalangeal joints and 1 st metacarpophalangeal (MCP) joint are assessed – (20 joints in total). First carpo-metacarpal joint changes were more common in NOA, but had little discriminatory value. Periarticular erosion and NBF are the key indicators and either feature must be present on the radiographs. Asymmetry of the findings and soft tissue oedema are also included. Each radiographic feature is scored between 0 and 2 (0=normal, 1=mild/moderate, 2=severe). The scoring system allows the identification of PsA features, even in the presence of background NOA. This scoring system is currently undergoing validation. <h3>Conclusions</h3> This radiographic interpretation and scoring system provides a clear framework with key discriminators and relative major and minor weighting. Once validated, it could be taught and used as a readily available, low-cost imaging tool, by both radiologists and non-radiologists alike. <h3>References</h3> [1] McGonagle D. Imaging the joint and enthesis: insights into the pathogenesis of psoriatic arthritis. Ann Rheum Dis. 2005;64[supple 2]:ii58-ii60. [2] Offidani A, Cellini A, Valeri G, Giovagnoni A. Subclinical joint involvement in psoriasis: magnetic resonance imaging and x-ray findings. Acta Derm Venereol1998;78:463–465. [3] Spira D, Kotter I, Henes J, et al. MRI findings in psoriatic arthritis of the hands. AJR Am J Roentgenol2010;195:1187–1193. [4] Bahadur S, et al. Psoriatic arthritis and nodal osteoarthritis can be differentiated using hand radiographs: a novel method, EULAR2017. <h3>Disclosure of Interest</h3> R. Mandegaran: None declared, E. Nikiphorou: None declared, S. Bahadur: None declared, C. Hughes: None declared, B. Kirkham Grant/research support from: Abbvie, Novartis, Roche, UCB, Paid instructor for: Eli Lilly and Co, Janssen, Novartis, A. Zavareh: None declared