A dyssomnia is a primary disorder of sleep or wakefulness
characterized by inability to sleep (ie, insomnia) or
excessive sleepiness (ie, hypersomnia). Dyssomnias are
disorders of duration, quality, and timing of sleep. The
prevalence of sleep-related problems in the general
population is estimated to be around 30%, affecting
between 50 and 70 million Americans of all ages.1
The
incidence and prevalence of sleep disorders are even
higher in the psychiatric population. Ford and Kamerow2
revealed that 40% of patients with insomnia and
46.5% of patients with hypersomnia had a psychiatric
disorder compared with only 16.4% of patients with no
sleep complaints.
Normal sleep is divided between rapid eye movement
(REM) and non-REM cycles. Non-REM sleep is
separated into 4 stages based on increasing depth of
sleep, which can be observed through polysomnography
(PSG). Sleep latency (ie, the time spent trying
to fall asleep) is normally 10 to 20 minutes. In stage 1
sleep, the occipital dominant rhythm decreases, and
the 8 to 13 Hz alpha waves seen in the awake state
diminish. Alpha waves are replaced by 3 to 7 Hz theta
waves, and larger vertex transients can be seen. In
stage 2, bursts of 12 to 15 Hz waves known as sleep
spindles occur, along with high voltage waves of positive
and negative polarity known as K complexes. In stage 3,
slow wave activity of 1 to 3 Hz known as delta waves are
observed, which comprise 20% to 49% of the stage 3
sleep period. Stage 4 consists of over 50% delta waves.
Stages 3 and 4 of non-REM sleep are more prominent
in the first half of normal sleep (Figure 1).3
REM accounts for 20% to 25% of sleep and is associated
with vivid dreaming. All muscles except for ocular
and respiratory muscles are paralyzed during REM to
prevent acting out dreams. REM normally starts around
60 to 90 minutes after sleep onset and is most prominent
in the latter half of sleep. REM and non-REM
usually occur in 90- to 110-minute cycles.4
Age-related
degenerative changes occur in the sleep cycles that lead
to a reduction of sleep efficiency (Table 1); however,
the overall need for sleep does not decrease with age.5