We have verified the eligibility of the Idiopathic Hypersomnia Severity Scale (IHSS) as a basic clinical tool for determining the subjective severity of illness in patients with idiopathic hypersomnia (IH) in the Czech Republic. Total of 37 patients with a diagnosis of IH (9 men, 28 women, mean age 40.2 ± 12.8) completed the IHSS scale. At the same time, they were instructed to complete the Epworth Sleepiness Scale (ESS), the Fatigue Severity Scale (FSS), the Hospital Anxiety and Depression Scales (HADS-A and HADS-D), and a short version of the Quality of Life Questionnaire (SF-36). The control group consisted of 88 age- and sex-matched healthy volunteers. The IHSS scale showed good internal consistency of the questionnaire using Cronbach's α, which was 0.88. The KMO (Keiser-Meyer-Olkin index) was 0.72, confirming sufficient structural validity of the questionnaire. The correlation of the total IHSS score with the ESS (ρ = 0.59, p=0.0001) and FSS (ρ = 0.84, p<0.0001) as well as with the HADS-A scales (ρ = 0.64, p<0.0001), HADS-D (ρ = 0.79, p<0.0001) and SF-36 in both the mental (ρ = -0.85, p<0.0001) and physical health (ρ = -0.66, p<0.0001) components. The IHSS is a convenient and easy-to-apply clinical tool to assess subjective severity of illness, which describes well the symptoms of idiopathic hypersomnia and assesses their impact on health and daily activities.

3rd Faculty of Medicine Charles University Prague Czech Republic

Department of Neurology and Center of Clinical Neuroscience 1st Faculty of Medicine Charles University and General University Hospital Prague Prague Czech Republic

Department of Sleep Medicine National Institute of Mental Health Klecany Czech Republic

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