Although earlier classifi cations allowed diagnosis
of idiopathic hypersomnia only in the context
of a prolonged nighttime sleep period, patients
with comparable daytime sleepiness but normal
to only slightly prolonged nighttime sleep have
been reported.19,21 As a result, idiopathic hypersomnia
without long sleep time has been established
as a separate diagnostic entity in ICSD-2.
Although the severe, pervasive daytime somnolence
and unrefreshing naps seen in this condition
are identical to those seen in idiopathic hypersomnia
with long sleep time, the nighttime sleep
period is 10 h.