The Narcolepsy Severity Scale (NSS) is reliable, valid, and responsive to changes in the severity of narcolepsy type 1, and should be used more frequently in clinical settings and future narcolepsy studies, according to study results published in Sleep.
According to researchers, a small proportion of patients with narcolepsy type 1 share the same 5 symptoms (excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis, and disrupted nighttime sleep); however, it is unclear whether these symptoms affect daily functioning and quality of life in narcolepsy type 1. The NSS was recently developed to evaluate the severity, frequency, and impact of the 5 main narcolepsy symptoms in patients with this sleep disorder. The objective of this study was to define clinically relevant NSS score ranges, confirm its main performances, test whether its items should be weighted, and reassess its responsiveness to narcolepsy medications in patients with narcolepsy type 1.
In this study, researchers recruited 381 patients with narcolepsy type 1 (143 untreated patients and 238 treated patients) from the National Reference Center for Narcolepsy of Montpellier, France. All patients completed the NSS based on the last month of their experience with the sleep disorder and were asked questions about the frequency and intensity of symptoms and the impact of symptoms on daily life. The Epworth Sleepiness Scale (ESS) was used to assess the presence and severity of excessive daytime sleepiness, and logistic regression models were used to compare the ESS with different NSS items.
Researchers revealed that the NSS total score was higher in patients who were untreated than those who were treated (33.34±9.40 vs 24.26±10.24, P <.0001) and that all NSS items were less severe in patients who were treated vs those who were untreated, except for items #2 and #5 (irresistible need to sleep during the day and worried about falling asleep during the day, respectively). Patients who were treated had fewer symptoms than patients who were untreated (P <.0001).
The number of symptoms was associated with diagnosis delay, age of onset of narcolepsy type 1, and ESS and Beck Depression Inventory scores. NSS total score was divided into 4 severity levels (mild, moderate, severe, and very severe), with differences between each group related to treatment. The probability of scoring high in the ESS and Beck Depression Inventory, and of scoring low in quality of life, increased with the severity level. Researchers found that NSS item weighting was not necessary to highlight differences between each group.
The study researchers concluded that the NSS is valid, reliable, and responsive to changes in severity level of narcolepsy type 1 and that it has adequate clinimetric properties for continued use in clinical and research settings.
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
Dauvilliers Y, Barateau L, Lopez R, et al. Narcolepsy Severity Scale: a reliable tool assessing symptom severity and consequences [published online January 29, 2020]. Sleep. doi: 10.1093/sleep/zsaa009