Longitudinal validation of the King’s Sarcoidosis Questionnaire in a cohort with mild sarcoidosis

<bold>Background:</bold> Quality of life is impaired in patients with sarcoidosis. The King’s Sarcoidosis Questionnaire (KSQ) is a brief questionnaire assessing health related quality of life in patients with sarcoidosis comprising subdomains of General Health status (GHS), Lung, Medication, Skin, and Eye. The aim of this study was to enhance the validation of the KSQ, incorporating longitudinal validation and known groups validity in a cohort with mild sarcoidosis. <bold>Methods:</bold> The KSQ was linguistically validated according to guidelines. Patients with sarcoidosis completed KSQ and other questionnaires at baseline, after two weeks and at 12 months. Forced vital capacity (FVC) was measured. Concurrent validity, reliability, and responsiveness were assessed. <bold>Results:</bold> In patients (n=150) the KSQ had moderate to strong correlations with the Short Form-12 (Mental Component Summary), the King’s Brief Interstitial Lung Disease Questionnaire and the Fatigue Assessment Scale (r=0.30-0.70) and weak for the Short Form-12 (Physical Component Summary) and forced vital capacity (FVC) (r= 0.01-0.29). The KSQ GHS and Lung domains were able to discriminate between groups of patients stratified according to fatigue, treatment, and FVC. KSQ had high internal consistency (Cronbach’s α = 0.73-0.90) and repeatability (interclass correlation coefficients = 0.72-0.81). Correlations to comparable questionnaires at baseline were moderate or strong for GHS, Lung, and GHS-Lung and weak or moderate to FVC. The KSQ was responsive to changes over time. <bold>Conclusion:</bold> This study strengthened the validation of KSQ by introducing known groups validity and assessments of responsiveness over 12 months in patients with mild sarcoidosis.