The diagnosis of narcolepsy can be made on clinical evidence alone, but objective assessment and documentation with polysomnography (PSG) and Multiple Sleep Latency Test (MSLT) is preferred to assess the severity of sleepiness, document the presence of sleep-onset REM periods, and rule out other sleep disorders.
The MSLT is the primary diagnostic test for narcolepsy. In untreated patients who have narcolepsy, the mean MSLT is short (less than five minutes), and two or more sleep-onset REM periods are observed.40 The MSLT should be performed after PSG, however, to first exclude other sleep disorders.
One caution, however, is that the MSLT has high rates of both false positive and false negative results. (For example, an MSLT narcolepsy diagnosis can occur for patients with Behaviorally Induced ISS.) The MSLT may need to be repeated for this reason.
- Littner MR, Kushida C, Wise M, et al. Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test. Sleep. 2005;28:113-121.