Comorbidity Profiles at Diagnosis in Rheumatoid Arthritis Versus Psoriatic Arthritis: A Nationwide Polish Claims-Based Study

Background: Nationwide epidemiologic data on comorbidity burden in early rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are limited. We compared coded diagnoses for concurrent disorders in incident RA and PsA based on administrative healthcare data (AHC). Methods: This retrospective cohort study used AHCs from the National Health Fund between 2009 and 2021. Using composite proxy definitions for RA and PsA diagnosis (combination of ICD-10 codes and prescription data), we identified all new cases of RA and PsA between 2019 and 2021. We utilized a ten-year lookback window for the accrual of concurrent disorder claims. Age-, sex-, serostatus- and calendar year-adjusted models were considered. Crude, relative and adjusted prevalence estimates were calculated using generalized linear models. Results: Using NHF data, we identified 36,285 and 1603 patients with incident RA/PsA, respectively. We estimated the burden of 31 multisystem comorbidities. Most disorders (N = 23, 74.2%) were more frequently coded among RA patients, while only liver diseases were significantly more prevalent in PsA. Chronic back pain (+21.2 pp) and osteoarthritis (+18.3 pp) were tied to the greatest absolute differences, likely mirroring medical contact patterns throughout the differential diagnostic process. Hospitalization due to heart failure and stroke, but not myocardial infarction, was more common in RA vs. PsA. Conclusions: Newly diagnosed patients with RA and PsA show distinct patterns of healthcare utilization for multiple organ disorders. Early RA may be tied to higher comorbidity rates not fully explained by age and sex, as compared to PsA; further studies are necessary to clarify these observations.