The objectives of this study were to document symptoms and health-related quality of life (HRQoL) impacts of idiopathic hypersomnia (IH) and evaluate content validity of the Idiopathic Hypersomnia Severity Scale (IHSS).

IH is characterized by excessive daytime sleepiness (EDS), sleep inertia, and prolonged nighttime sleep. Patients with IH experience reduced HRQoL. The IHSS measures symptom severity and impacts, and responsiveness to treatment. 

Interviews were conducted with adults with IH and had an open-ended concept-elicitation (CE) section (for descriptions of signs, symptoms, and HRQoL impacts) and a scripted “think aloud” cognitive debrief (CD) section assessing content validity of the IHSS. Targeted questions were asked to assess readability, relevance, and comprehensiveness. Participants were asked what point changes they considered to represent clinical meaningfulness.

Interviews were conducted with 20 participants (mean age, 35.0 years; 70.0% female; 90.0% White/Caucasian). Frequently reported symptoms were EDS and sleep inertia. EDS was reported as the most bothersome symptom (n=14/20, 70.0%) and rated as most important to treat (n=15/20, 75.0%). Nearly all participants reported that IH negatively impacted multiple life domains, including emotional, cognitive, and work domains. Cognitive difficulty was rated as the most bothersome (n=6/20, 30.0%) and most important functional domain to treat (n=8/20, 40.0%). Most participants (n=17/20, 85.0%) were able to read, comprehend, and interpret instructions, items, and response options for the IHSS; any difficulties were idiosyncratic and reported by single participants. No major interpretation issues were reported. Participants articulated a range of changes (1- to 2-point difference in a scale item) as meaningful improvement. No modifications to the IHSS were recommended.

Findings indicate that adults with IH experience many symptoms that negatively impact multiple domains of HRQoL, highlighting unmet medical needs for IH treatment. They also provide evidence of IHSS content validity, demonstrated as ease of completion, comprehensibility, and interpretability.