use MSLT to diagnose narcolepsy and hypersomnia

  • multiple sleep latency test
  • take 4-5 daytime naps about 2 hours apart
  • measure how long takes to fall asleep
  • if not fall asleep in 20 minutes: sleep latency 20 min
  • if fall asleep: record brain activity for 15 min to see if reach REM
  • < 8 min latency: could be narcolepsy, and more likely to enter REM
  • idiopathic: less than 8 min latency but less likely to enter REM1
  • This clinical history is consistent with classic presentation of narcolepsy type 1 (narcolepsy with cataplexy). Narcolepsy is diagnosed by overnight polysomnogram followed by MSLT, a validated objective measure of the tendency to fall asleep (choice D is correct).

Classic symptoms of narcolepsy include chronic hypersomnia (longer than 3 months) despite adequate sleep duration, naps that tend to be refreshing for a short period of time, sleep paralysis, and vivid visual, tactile, or auditory hallucinations that occur as the patient is falling asleep (hypnagogic hallucinations) or waking up (hypnopompic hallucinations). This patient also has cataplexy, which consists of emotionally triggered transient muscle weakness. In most patients, cataplexy is generally triggered by intense positive emotions such as laughter, joking, or excitement. Less frequently, however, cataplexy may be brought about by anger or frustration. Typically, during a cataplexy episode, muscle weakness starts with the facial muscles (ie, ptosis; a slack, open mouth; loss of facial expression). In severe cases, the patient may lose muscle tone to the extremities and collapse. Importantly, consciousness remains intact during cataplexy, and weakness usually resolves in 1 to 2 min. Patients with narcolepsy type 2 do not have cataplexy.

MSLT is preceded by nocturnal polysomnogram to ensure that the patient has adequate sleep duration the night prior to MSLT (ideally more than 6 h) and to rule out other sleep disorders such as sleep-disordered breathing and periodic limb movement disorder. Poor sleep efficiency on the polysomnogram and untreated sleep apnea can lead to an abnormal MSLT and if present, MSLT should be canceled. MSLT consists of five 20-min nap opportunities performed at 2-h intervals. The first nap begins 1.5 to 3 h after the patient's usual wake-up time. During each nap opportunity, the patient is instructed to try to fall asleep. If no sleep occurs, the nap opportunity is ended after 20 min, and sleep latency is measured as 20 min. The diagnosis of narcolepsy is made if mean sleep latency across the five naps is ≤8 min and at least two of the naps have sleep-onset REM periods. Narcolepsy can also be diagnosed if the MSLT shows a mean sleep latency of ≤8 min and one sleep-onset REM period as long as the preceding overnight polysomnogram has a REM sleep latency of less than 15 min. For diagnosis of narcolepsy type 1, there must be a history of cataplexy or a low level of hypocretin in the cerebrospinal fluid (<110 pg/mL). A polysomnogram without MSLT can be helpful in diagnosing sleep-disordered breathing, periodic limb movement disorders, and certain parasomnias, but narcolepsy cannot be diagnosed without an MSLT. A home sleep test is a diagnostic tool for OSA, not narcolepsy. In this patient, home sleep test is not an appropriate diagnostic test because the pretest probability for OSA is low (choice A is incorrect).

Management of narcolepsy consists of treating the symptoms, given that there are no disease-modifying therapies available. In addition to good sleep hygiene and strategic napping, pharmacotherapy is used to improve alertness during the day to improve the patient's quality of life and functionality. Wake-promoting agents such as modafinil, armodafinil, and pitolisant may be sufficient for patients who have a mild to moderate degree of hypersomnia. In those who are refractory to these first-line agents, methylphenidate and amphetamines can be considered. Sodium oxybate indirectly improves daytime sleepiness by consolidating nighttime sleep; it also improves cataplexy.

Footnotes

  1. https://www.sleepfoundation.org/how-sleep-works/sleep-latency ↩