Narcolepsy severity scale and its psychometric properties in patients with narcolepsy type 1 in the Czech Republic
Abstract
Aim: The aim of the study was to verify the applicability of the Narcolepsy Severity Scale (NSS) as a basic clinical tool for determining the subjective severity of the disease in patients with narcolepsy type 1 (NT1) in the Czech Republic. Patients and methods: A total of 78 patients from 2 sleep centers with a dia-gnosis of NT1 (29 men, 49 women, mean age 36.1 +- 11.7 years, range 18-71 years, N = 51 were treated) completed the NSS scale consisting of 15 questions focusing on the occurrence, frequency, and impact on daily activities of all major narcoleptic symptoms.
At the same time, they were instructed to complete the Epworth Sleepiness Scale (ESS), the Fatigue Severity Scale (FSS), the Hospital Anxiety and Depression Rating Scale (HADS) and a short version of the Quality of Life Questionnaire (SF-36). Results: The NSS scale shows good internal consistency of the questionnaire using Cronbach's a, which is 0.80 for the whole cohort of NT1 patients, 0.79 for the treated group and 0.82 for the untreated group.
The Keiser-Meyer-Olkin index for the entire cohort is 0.73, confirming sufficient structural validity of the questionnaire. There was no significant difference in the NSS scores of treated and untreated patients; however, the correlation of the total NSS score with ESS (ρ = 0.61; P < 0.0001) and FSS (ρ = 0.4438; P < 0.0001) was confirmed.
Conclusions: The NSS is a convenient and practical clinical tool for determining the subjective severity of the disease, well capturing the main narcoleptic symptoms and assessing their impact on daily activities.