Study Finds Some Sleep Measures Can Distinguish Between Narcolepsy Types
A new study has identified certain sleep measures that can reliably distinguish between narcolepsy type 1 (NT1) and type 2 (NT2).
A recent study published in the journal SLEEP has shed light on the differences between narcolepsy type 1 (NT1) and type 2 (NT2). Researchers found that some measures used to diagnose these conditions are more trustworthy than others.
Narcolepsy type 1 (NT1) is characterized by the loss of orexin and the presence of cataplexy, a distinctive symptom. NT2 symptoms are generally milder, but variability in sleep testing makes it harder to diagnose. The study aimed to identify which sleep measures can reliably distinguish between NT1 and NT2.
The researchers used data from two clinical trials, following 37 people with narcolepsy-17 with NT1 and 19 with NT2-over three visits, four weeks apart. During each visit, participants underwent an overnight polysomnography (PSG) and a next-day Maintenance of Wakefulness Test (MWT).
| Measure | NT1 | NT2 |
|---|---|---|
| qEEG features | remarkably stable | rarely differentiated NT1 from NT2 |
| Sleep architecture | more useful for distinguishing diagnosis | |
| Wakefulness | NT1 consistently fell asleep faster than NT2 | |
| Hypnodensity analysis | strong reliability, wake-REM mixed features distinguished between NT1 and NT2 | |
| Sleep fragmentation | reproducible in repeat testing, measures included increased wake after sleep onset, greater N1 sleep, higher stage-shift indices, reduced N2 continuity, and increased transitions from N2 to wake |
The study found that quantitative electroencephalography (qEEG) measurements were the most consistent from visit to visit, but "the most reliable measures were not necessarily the most clinically informative," says Emily Schlafly, PhD, a postdoctoral researcher at Takeda Pharmaceuticals who led the study.
Researchers found that measures of sleep architecture and wakefulness were more useful for distinguishing diagnosis. Participants with NT1 consistently fell asleep faster than those with NT2 during MWT sessions, with measurements considerably more reproducible in NT1 than NT2.
Hypnodensity analysis-an automated scoring method that shows the probability of mixed sleep states, rather than a single stage-also showed strong reliability, and wake-REM mixed features in particular could distinguish between NT1 and NT2.
However, further validation and clearer guidance on which metrics were most meaningful are needed. "As the field evolves, some of the most informative signals may come from the patterns visible within these hypnodensity plots," she says.
Measures of sleep fragmentation-including increased wake after sleep onset, greater N1 sleep, higher stage-shift indices, reduced N2 continuity, and increased transitions from N2 to wake-were not only different between groups, but they were also reproducible in repeat testing.
The study highlights the importance of understanding the stability of sleep measures within an individual over time. "Not all sleep metrics are equally reliable or equally useful clinically. Before we can confidently use a measure to monitor disease or treatment response, we need to understand how stable it is within an individual over time," Schlafly says.
