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Abstract
Objective To validate the Idiopathic Hypersomnia Severity Scale (IIHSS), a self-report measure of hypersomnolence symptoms, consequences, and responsiveness to treatment.
Methods The 14-item IHSS (developed and validated by sleep experts with patients' feedback) was filled in by 218 participants (2.3% missing data). Among the 210 participants who fully completed the IHSS, there were 57 untreated and 43 treated patients with idiopathic hypersomnia (IH) aged 16 years or older, 37 untreated patients with narcolepsy type 1 (NT1), and 73 controls without sleepiness. IHSS psychometric properties, discriminant diagnostic validity, and score changes with treatment were assessed.
Results The IHSS showed good internal consistency and content validity. Factor analysis indicated a 2-component solution with good reliability expressed by satisfactory Cronbach α values. IHSS scores were reproducible without changes in the test–retest evaluation (13 treated and 14 untreated patients). Convergent validity analysis showed that IHSS score was correlated with daytime sleepiness, depressive symptoms, and quality of life in patients with IH. The IHSS score was lower in treated than untreated patients (5–8 unit difference, without ceiling effect). The cutoff value for discriminating between untreated and treated patients was 26/50 (sensitivity 55.8%, specificity 78.9%). IHSS scores were higher in drug-free IH patients than NT1 and controls. The best cutoff value to differentiate between untreated IH patients and controls was 22 (sensitivity 91.1%, specificity 94.5%), and 29 with NT1.
Conclusions The IHSS is a reliable and valid clinical tool for the quantification of IH symptoms and consequences that might be useful for patient identification, follow-up, and management.
Glossary
- AUC=
- area under the curve;
- BDI-II=
- Beck Depression Inventory II;
- BMI=
- body mass index;
- CI=
- confidence interval;
- EDS=
- excessive daytime sleepiness;
- EQ-5D=
- European Quality of Life–5 Dimensions;
- EQ-VAS=
- European Quality of Life visual analog scale;
- ESS=
- Epworth Sleepiness Scale;
- ICC=
- intraclass correlation coefficient;
- ICSD=
- International Classification of Sleep Disorders;
- IH=
- idiopathic hypersomnia;
- IHSS=
- Idiopathic Hypersomnia Severity Scale;
- KMO=
- Kaiser-Meyer-Olkin;
- MSL=
- mean sleep latency;
- MSLT=
- multiple sleep latency test;
- NT1=
- narcolepsy type 1;
- NT2=
- narcolepsy type 2;
- PSG=
- polysomnography;
- ROC=
- receiver operating characteristic;
- SOREMP=
- sleep-onset REM period
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received July 20, 2018.
- Accepted in final form December 7, 2018.
- © 2019 American Academy of Neurology
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