Psoriasis is a chronic, immunological and systemic disease with an estimated prevalence of about 2-3 percent. Psoriasis is associated with the joint disease psoriasis arthropathy. There are several treatments options available for psoriasis and patients with moderate to severe psoriasis generally need systemic agents. In 2004 biologics were introduced for patients with moderate to severe psoriasis in Sweden.
The overall objective of this thesis was to assess the relationship between Health Related Quality of Life (HRQOL) and clinical outcome measures in psoriasis patients, to analyse the effectiveness of biologics in psoriasis in everyday clinical practice and to explore how costs of the psoriasis population changed after the introduction of biologics in Sweden.
Methods: Research was based on national administrative registers and PsoReg, the Swedish registry for systemic treatment of psoriasis. In a cross-sectional study (paper I) the three outcome measures: the generic HRQOL measure EQ-5D, the dermatology specific HRQOL measure the Dermatology Life Quality Index (DLQI) and the clinical measure of skin involvement, Psoriasis Area and Severity Index (PASI), were analysed by demographic characteristics. The generic EQ-5D among psoriasis patients was compared to previously published values for the general population in Sweden. Relationships between measures were examined with correlation tests and regression analysis. A longitudinal study included patients registered in PsoReg who switched to a biologic agent for the first time during registration (paper II). The three outcomes EQ-5D, DLQI, and PASI were analysed before and after switch in the overall patient group and in subgroups. The relative effectiveness of continuing with the standard care of conventional treatment compared to switching from standard care to biologics was analysed in patients with moderate to severe psoriasis (paper III). Patients in PsoReg were matched with propensity scores and average treatment effects were estimated. The estimated outcomes were the change of EQ-5D, DLQI, and PASI. Patients were identified in national registers at the National Board of Health and Welfare when analysing costs; either by a registration of a psoriasis diagnosis in the national patients register and/or by a registration in the prescribed drugs register of a topical treatment with calcipotriol, a substance which has the indication psoriasis only (paper IV). Direct costs included patients’ visits in specialist health care and prescribed drugs used for psoriasis treatment, retrieved from the national patients register and the prescribed drugs register, respectively. Indirect costs included productivity loss in terms of sick leave and disability pension, which estimated as excess costs compared to controls. Controls were selected from the normal population and matched on sex, age and municipality. Productivity loss was estimated based on data from the Longitudinal integration database for health insurance and labour market studies at Statistics Sweden.
Results: Patients with moderate to severe psoriasis had significantly lower HRQOL in EQ-5D than the general population (paper I). Women rated their HRQOL lower than men, even though men had more severe clinical skin involvement than women. (paper I). The generic measure EQ-5D and the dermatology-specific DLQI had moderate correlations whereas EQ-5D had low correlation with the clinical measure PASI (paper I). Patients who switched to a biologic agent during registration in PsoReg had significant improvements in all outcomes (paper II). Patients who fulfilled the criteria for moderate to severe psoriasis had the highest benefits of the biologic agents (paper II). The matched conventionally and biologically treated patients with moderate to severe psoriasis were essentially equal in important observable variables (paper III). The subgroup of patients not responding to conventional treatment had high potential benefits of biologic agents (paper III). Individuals with psoriasis had sick leave and disability pension to a larger extent than their matched controls (paper IV). Direct costs increased, whereas the indirect costs of productivity loss decreased between 2006 and 2009 (paper IV).
Conclusion: Psoriasis is associated both with direct costs and indirect costs, and it has a negative impact on patients’ HRQOL. When evaluating psoriasis treatments and making decisions about treatment guidelines, both generic, dermatology-specific HRQOL measures, and clinical measures are necessary; as they answer to different needs. Although dependent on data quality, generalisability, and current pricing, results suggest that conventional treatments are suitable as first line and biologic agents as second line treatment. Results indicate that the different types of systemic treatments are not allocated optimally among patients with psoriasis in Swedish clinical practice.