In preadolescence, mean latencies less than 15
iNnutes are abnormal and suggest significant
sleepiness. REM sleep is normally not present
during any daytime nap. If PSG and MSLTs are
being performed in individuals with circadianrhythm
disorders, it is very important that the PSG
be timed to coincide with the patients habitual
sleep time. Practically, this means the patient
should not be arbitrarily awakened at a specific
time in the morning to end the night-time study and
to begin the MSLT. If this recommendation is not
followed, some patients will be misdiagnosed as
having a primary sleep problem, such as narcolepsy,
when in fact their symptoms of sleepiness
are the result of chronic sleep insufficiency often
seen with delayed sleep-phase syndrome (DSPS).
This pitfall will be further illustrated in the case
descriptions.