Background/Purpose: Spondylitis in Psoriatic Arthritis (PsA) sometimes resembles DISH because of the presence of juxta-vertebral calcification that resemble syndesmophytes. Distinguishing spondylitis from DISH has therapeutic and prognostic implications. The purpose of this study was to determine the prevalence of DISH in PsA patients and to identify features associated with its occurrence.

Methods: PsA patients were recruited from a single centre prospective observational cohort initiated on 1978. All patients fulfilled the CASPAR criteria and were assessed every 6-12 months according to a standard protocol which included a detailed history, physical examination and laboratory evaluation. Radiographs of peripheral joints and spine were obtained every 2 years. DISH was defined as flowing bony bridges in at least 4 contiguous thoracic vertebrae irrespective of the presence of radiographic sacroiliitis on the last radiographic assessment. Each PsA patient with DISH was matched by sex to 3 PsA patients without DISH recruited to the clinic within a year. Demographics and disease characteristics were compared in both groups including age, disease duration, BMI, comorbidities (myocardial infarction, angina, diabetes, hypertension), uric acid levels, ESR and CRP. The radiographic features that were assessed included the presence of sacroiliitis, syndesmophytes at cervical, thoracic and lumbar spine, and calcaneal spurs. Descriptive analyses and comparisons were conducted using McNemar test, Fisher’s exact test and Chi-squared test for categorical variables and paired t-test for continuous variables. Logistic regression analyses using univariate and multivariate models with stepwise regression were conducted.

Results: Of 938 PsA patients, DISH was observed in 78 patients with a prevalence of 8.3%. Patients with DISH were older (62.9 vs 49.3, P<0.0001), had a longer disease duration (15.1 vs 12.8 years, P<0.003), a higher BMI (32.9 vs 28.7, P<0.0001), had more diabetes (28% vs 9.8%, P<0.0001), hypertension (50% vs 24.9%, P<0.0001) and higher uric acid levels (16% vs 7%, P=0.02).The modified Steinbrocker score  was also higher in patients with DISH (32.0 ± 39.8 vs. 19.5 ± 31.4, P=0.0001). The presence of inflammatory back pain, HLA-B*27 allele and sacroiliitis was similar in both groups. The difference in ESR and CRP was not clinically significant. However, patients with DISH had more syndesmophytes (38.5% vs 18.7%, P<0.0001) and calcaneal spurs (83.3% vs 60.9%, P<0.0001). Patients with DISH and syndesmophytes had more sacroiliitis (65% vs 38%, P=0.02) than patients with no syndesmophytes. Older age, higher BMI and the presence of radiographic damage to peripheral joints were associated with DISH in the multivariate analysis with an odds ratio of 1.13 95%CI(1.07-1.19), 1.19 95%CI(1.09-1.29) and 5.22 95%CI(1.35-20.13) respectively.

Conclusion: DISH was associated with known DISH related factors including older age and high BMI, as well as the presence of radiographic damage to peripheral joints. The diagnosis of DISH is possible in the presence of psoriatic spondylitis. The presence of sacroiliitis was similar but syndesmophytes were higher in patients with DISH.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/diffuse-idiopathic-skeletal-hyperostosis-dish-in-psoriatic-arthritis/