wHAT SORT OF LABORATORY TESTS CAN HELP IDENTIFY NARCOLEPSY?

wHAT SORT OF LABORATORY TESTS CAN HELP IDENTIFY NARCOLEPSY?

The multiple sleep latency test (MSLT): An objective measurement of daytime physiology.

The MSLT is indicated, together with polysomnography (PSG), as part of the evaluation of patients with suspected narcolepsy.1

  • The MSLT is performed immediately following overnight polysomnography to confirm the diagnosis.1
    • Performing an MSLT following a complete night of polysomnography is important since sleep latency is influenced by the quantity of prior sleep.1
    • The MSLT also should not be performed after a split-night sleep study, as its value in supporting a narcolepsy diagnosis may be suspect if the total night sleep on the prior sleep period is less than 6 hours.1
  • The MSLT assesses...
    • The ability or tendency to fall asleep (as indicated by mean sleep latency, or time to sleep onset) during normal waking hours.1,2
    • The presence of sleep onset rapid eye movement periods (SOREMPs).1,2
  • Measurements are taken during four or five 20-minute nap opportunities at 2-hour intervals.1,3
  • Normally, mean sleep latency is more than 10 minutes and SOREMPs (REM sleep onset less than or equal to 15 min) usually do not occur.2,4
  • In narcolepsy, mean sleep latency is 8 minutes or less and a SOREMP will occur during at least 2 of the 4 or 5 daytime nap periods.1-4

Interpreting MSLT results.*

Normal Sleep2,4
  • Mean sleep latency is more than 10 min.
  • SOREMPs are usually absent.
Sleep Suggestive of Narcolepsy1-4
  • Mean sleep latency is 8 min or less.
  • Two or more SOREMPs are present.

*At least 1 week of actigraphy assessment with a sleep log is strongly recommended prior to an MSLT to determine factors that may bias results (eg, insufficient sleep, shift work, or other circadian rhythm disorder). Patients should be free of drugs that influence sleep for at least 14 days (or at least 5 times the half-life of the drug and longer-acting metabolite) before performing an MSLT.2

A SOREMP on an overnight PSG can be used as 1 of the 2 or more SOREMPs necessary for a narcolepsy diagnosis according to the ICSD-3 (International Classification of Sleep Disorders, 3rd ed.2) criteria.