Burden of disease in psoriasis and psoriatic arthritis. Occurrence, healthcare use, costs and health outcomes.

Psoriasis (PSO) and psoriatic arthritis (PsA) are two related chronic inflammatory diseases. A proportion of people with PSO also develop PsA. PSO and PsA seem to have multiple impacts; from the health and well-being of the individual; to the need for healthcare resources for disease management; to the loss of productivity. Compared with other chronic diseases, such as heart disease and diabetes, population-based observational healthcare research on PSO and PsA is limited. The overall aim of this thesis was to study the impact of PSO and PsA in terms of occurrence, costs, healthcare use and patient-reported outcomes (PROs), from a population-based perspective. The included studies used data related to residents in the Skåne region, and the study populations were identified in the Skåne Healthcare register (SHR). Information was based mainly on population-based registers but also on surveys and medical records. The point prevalence of physician-diagnosed PSO with or without PsA in the Skåne region by the end of 2010 was 1.2%, corresponding to 12,958 diagnosed individuals. The prevalence for PSO alone and PSO with PsA was 1.0% and 0.2% respectively. The ICD-10 diagnostic codes registered for PSO and PsA in the SHR showed overall good accuracy when compared to information in medical records. The annualized mean societal cost for PSO patients with PsA was 97% higher compared with PSO alone patients (€17,600 vs. €8,900). Only a minor fraction of the costs was identified as attributable to PSO and PsA specifically, indicating increased comorbidity in these patients.Analyses on healthcare use among PSO and PsA patients, and population-based matched referents, indicated remaining disparities in the socioeconomic pattern of healthcare use, especially related to income. The effect was less accentuated for PSO and PsA compared to referents. Regarding PROs, we showed that, in a cohort of PsA patients, continuous and never users of biological drugs, which were the majority of the patients, reported better PROs and lower societal costs compare to irregular users of biological drugs.This thesis contributes with knowledge on the impact of PSO and PsA from different perspectives, that can be useful both for researchers and policy makers. In addition, the work also adds information on data quality, and methods for prevalence and cost calculations using register-based data