Background:The prevalence of osteoporosis in inflammatory rheumatic diseases such as psoriatic arthritis (PsA) has not been sufficiently clarified yet, and the data in the literature are heterogeneous. In addition, it is still unclear to what extent patients with PsA differ in terms of bone density from patients with other forms of spondyloarthritis such as ankylosing spondylitis (AS).Objectives:In an interim analysis of the Rh-GIOP Study (ClinicalTrials.gov IdentifierNCT02719314), we observed that PsA patients demonstrated more frequently normal bone density than any other patient group analyzed (suffering from e.g. rheumatoid arthritis or systemic sclerosis). The main objective of this investigation was to compare bone density data from patients with PsA and AS, as both diseases belong to the spondyloarthritis group. 1100 patients with inflammatory rheumatic diseases provided the basis of Rh-GIOP, a prospective study monitoring glucocorticoid (GC)-induced osteoporosis in patients with rheumatic diseases. Rh-GIOP was established in 2015 at the Charité University Hospital. Bone mineral density data were measured by dual x-ray absorptiometry (DXA).Methods:92 patients with PsA (65% female) were compared with 51 patients suffering from AS (35% female). Potential risk and protective factors (e.g. data on GC treatment, anti-rheumatic therapy), laboratory parameters (e.g. Vitamin D, alkaline phosphatase, calcium and inflammatory markers) and functional status (e.g. Health Assessment Questionnaire, sporting activities, back pain) were compared between these groups. Statistical analysis was performed descriptively using mean and standard deviation, t-tests for metric variables, and chi-square tests for nominal variables. Due to the heterogeneous gender distribution, an additional statistical matching was performed to compare patients matched by age and gender.Results:Patients with PsA displayed significantly higher minimal T-scores than patients with AS (p=0.003) even though patients with AS were younger and more often male (p<0.001). AS patients showed a higher frequency of osteopenic bone densities (p<0.05), however, no differences in the frequency of osteoporotic bone densities were found. Body-mass-index (BMI) was significantly higher (p<0.001) in PsA patients. PsA patients demonstrated a higher frequency of csDMARD use (p<0.001). Additional analyses among PsA patients with and without csDMARDs revealed also significantly higher minimal T-scores in PsA patients taking csDMARDs (90% Methotrexate), and both groups showed the same average of age and gender distribution. Furthermore, AS patients complained significantly more often of back pain (96 % vs. 74%, p=0.001) than PsA patients. No differences in GC use or cumulative GC dose were found. All results could be confirmed when groups were matched by age and gender.Conclusion:Our results demonstrate that patients with PsA display higher bone density compared to age and gender matched patients with ankylosing spondylitis. Possible influencing factors could be the higher frequency of csDMARD use, higher BMI or the lower frequency of back pain in PsA patients. Multivariate tests and additional biomarker investigations in larger cohorts are necessary to corroborate these findings and to identify underlying pathogenic differences which could serve for an explanation.Disclosure of Interests:Desiree Freier: None declared, Edgar Wiebe: None declared, Robert Biesen: None declared, Thomas Buttgereit: None declared, Sandra Hermann: None declared, Timo Gaber: None declared, Frank Buttgereit Grant/research support from: Amgen, BMS, Celgene, Generic Assays, GSK, Hexal, Horizon, Lilly, medac, Mundipharma, Novartis, Pfizer, Roche, and Sanofi.
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