Longitudinal validation of King's Sarcoidosis Questionnaire in a prospective cohort with mild sarcoidosis

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 Eyes. 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.

The KSQ was linguistically validated according to guidelines. Patients with sarcoidosis completed KSQ and other questionnaires at baseline, after 2 weeks and at 12 months. Forced vital capacity (FVC) was measured. Concurrent validity, reliability and responsiveness were assessed.

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 correlations with the Short Form-12 (Physical Component Summary) and 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. The 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 the GHS, Lung and GHS-Lung subdomains and weak or moderate for FVC. The KSQ was responsive to changes over time.

This study strengthened the validation of the KSQ by introducing known-groups validity and assessments of responsiveness over 12 months in patients with mild sarcoidosis.