Standardized documentation of health-related quality of life in patients with psoriatic arthritis Validation of the German version of the psoriatic arthritis quality of life (PsAQoL) questionnaire

Background. The standardized assessment of health-related quality of life is becoming increasingly more important. The English questionnaire on psoriatic arthritis quality of life (PsAQoL) is a disease-specific instrument for measuring the quality of life of patients with psoriatic arthritis (PsA). The aim of the present study was to translate the PsAQoL into German and to validate the German version in a cohort of PsA patients recruited from routine care. Method. The translation and validation of the PsAQoL questionnaire was carried out in a stepwise procedure involving affected patients with PsA. After translation of the original English questionnaire the German version was evaluated in a field test. The psychometric features of the questionnaire were then examined in a PsA cohort from routine care. In addition to the construct and group validity, the reliability of the questionnaire was tested using test-retest reliability and internal consistency. The physical functioning was measured with the health assessment questionnaire (HAQ) and domains of the quality of life with the Nottingham health profile (NHP). Results. In a field test with 10 patients the German version of the PsAQoL questionnaire proved to be relevant, easily understandable and feasible (processing time 4.7 +/- 2.1 min). A total of 126 patients (37.3% male, age 55.6 +/- 11.3 years) were included in the validation cohort. The PsAQoL showed moderate correlation with the HAQ (r = 0.65) and moderate to good correlation with the NHP (subdomains r = 0.58-0.75). The internal consistency was high (Cronbach's alpha 0.92) and reliability in patients with stable disease course was very good (Spearman correlation coefficient 0.94). The PsAQoL can differentiate between different patient groups. Conclusion. The German translation of the PsAQoL provides a valid disease-specific instrument for the standardized assessment of health-related quality of life in patients with PsA. The psychometric characteristics of this questionnaire are comparable with the original English version. The German PsAQoL can therefore be recommended for clinical and scientific application.