Ab0961 the Frequency of Diffuse Idiopathic Skeletal Hyperostosis (Dish) in Spondyloarthritis in Comparison to Age and Sex-Matched Controls and Impact of Spa on Onset Age of Dish

Background: The literature suggests the possibility of an increased prevalence of cervical diffuse idiopathic skeletal hyperostosis (DISH) in spondyloarthritis (SpA), based on case reports or studies that were not designed to investigate this specific question. Objectives: Our aim is to compare the frequency of cervical DISH in SpA vs age and sex-matched controls to see whether there is a true increased frequency and if the presence of SpA impacts the onset age of DISH. Methods: Adult patients with age ≥18 were included. The SpA population included patients who were diagnosed with axial or peripheral SpA, followed at the Arthritis Centre and had cervical spine x-rays for screening purposes in keeping with the standard of practice of a single rheumatologist between 2016-2020. The control group included patients who presented to the Emergency Department and had a cervical spine x-rays for any reason, and there were 4 control patients for each SpA patient who were age and sex-matched. An investigator meeting on the definitions took place prior to the study, followed by an agreement exercise. Two radiologists independently scored the xrays for the level of confidence for the presence of DISH, on a scale between 0-5. The ICC of the two radiologists were 0,935. For the study, the xrays were read by one of the two radiologists for any new bone formation, flowing ossification, bony spur, osteophyte, exuberant osteophytosis, syndesmophyte, floating mineralization, bridging and facet joint ankylosis and overall impression; equally distributing the cases and controls among the two radiologists. The confidence of ≥Grade 3 was considered DISH positive. Here, we present the data on DISH only. Results: One hundred ninety-one SpA and 764 age- and sex-matched controls were included. The mean (SD) age of SpA patients was 45.6 (13.4) years and 87 (45.5%) were women, being similar to the controls (p=1.00 and p=1.00, respectively). Eighty-three patients (43.4%) were diagnosed with psoriatic arthritis, 78 (40.8%) patients with radiographic axial SpA, 20 (10.5%) patients with non-radiographic axial SpA, and 10 (5.3%) patients with inflammatory bowel disease-related SpA. Within the whole group, 81 (42.4%) had isolated axial involvement according to the following rheumatologist, 36 (18.8%) had peripheral involvement, and 74 (38.7%) had axial and peripheral involvement. DISH was observed in 26 (13.6%) SpA patients and 108 (14.1%) controls, with similar frequency (p=0.852). The age of DISH+ patients was statistically significantly lower in the SpA group than the control group (median (IQR); 54 (16) vs 59 (13); p=0.026) (Figure 1). DISH was higher in males in both SpA and control groups (p=0.04 and p=0.003, respectively). There were 143 (74.9%) SpA patients with known HLA-B27 status. The frequency of DISH in HLA-B27(-) SpA patients was higher than HLA-B27(+) SpA patients numerically (n=14/65 (21.5%) vs n=8/78 (10.3%); p=0.063). Interestingly, HLA-B27 had different effects on the presence of DISH in subgroups: AxSpA patients (radiographic and non-radiographic combined) had more DISH if they were HLA-B27 positive (12.5% vs 8.7%), unlike the psoriatic arthritis patients, who had DISH exclusively if they were HLA-B27 negative (28.2% vs 0%). Conclusion: The frequency of DISH in SpA patients was found to be similar to the general population. However, SpA patients tended to develop DISH at an earlier age. Our observation on the differential impact of HLA-B27 on axSpA vs PsA may be a signal on the different mechanisms impacting the spine in both diseases. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: Sibel Aydin Abbvie, Jannsen, Novartis, Pfizer, and UCB, Abbvie, Celgene, Eli Lilly, Novartis, Pfizer, Sanofi, and UCB, Abbvie, Celgene, Eli Lilly, Jannsen, Novartis, Pfizer, Sanofi, Novartis, and UCB, Nicole Hryciw: None declared, Baljot Chahal: None declared, Seyyid Bilal Açikgöz: None declared, Gizem Ayan: None declared, Ummugulsum Gazel: None declared, Zaid Jibri: None declared, Marcos Loreto Sampaio: None declared.