Qualitative evidence on EQ-5D-5L skin irritation and self-confidence bolt-ons in Darier's disease and Hailey-Hailey disease

Objectives: Limited evidence is available about the content validity of the EQ-5D-5L in rare skin fragility disorders. Previous research has demonstrated that the skin irritation and self-confidence additional dimensions (bolt-ons) improve the content validity of the EQ-5D-5L in psoriasis and atopic dermatitis. Our aim was to investigate the content validity of the EQ-5D-5L and the two bolt-ons in Darier's disease and Hailey-Hailey disease.

Methods: In 2023, we conducted qualitative, semi-structured interviews with 15 adult patients at a university dermatology clinic. Patients completed the EQ-5D-5L with two bolt-ons using a think-aloud technique. We used probing questions to explore the relevance, comprehensiveness and comprehensibility. Thematic analysis was applied to analyze the transcripts from the interviews.

Results: Most patients found both the EQ-5D-5L and the two bolt-ons comprehensible and relevant to their disease. All patients preferred the EQ-5D-5L with the two bolt-ons over the EQ-5D-5L alone. Twelve potential missing concepts were identified after the EQ-5D-5L + bolt-ons, but only financial impact and sex life were identified by more than one patient. Only one patient reported a conceptual overlap between the skin irritation bolt-on and the pain/discomfort dimension.

Conclusions: Our findings suggest that there is no actionable evidence indicating gaps in the content validity of the EQ-5D-5L with two bolt-ons in Darier's and Hailey-Hailey disease. Future studies are encouraged to conduct quantitative psychometric testing of the bolt-ons in this and other chronic dermatological patient populations.