Sleep disorders

A review of the many abnormalities that arise from sleep is outside the scope of this brief review. However, sleep disorders such as periodic limb movements of sleep, REM sleep disorders, narcolepsy and cataplexy can be confused with seizures [60]. On the other hand some epilepsies arise exclusively from sleep and there is a propensity for partial seizures to occur in sleep or shortly after waking [61]. Benign rolandic epilepsy is an example of a seizure syndrome that is associated with sleep.

The parasomnias, including sleep walking, night terrors, restless legs, nocturnal myoclonus, bruxism, paroxysmal nocturnal dystonia and REM sleep disorder, can be more difficult to differentiate from seizures [62,63] whereas disorders with hypersomnolence rarely present diagnostic problems. Sleep disorders are common, particularly in the elderly.

Although the classic tetrad of narcolepsy involves excessive daytime sleepiness, cataplexy, hypnogogic or hypnopompic hallucinations and sleep paralysis, not every component occurs in a given individual. The diagnosis is based on sleep latency studies in which REM sleep begins abnormally early. Cataplexy, sudden episodes of sleep and hallucinations are sometimes misidentified as seizures

[64], Rarely, cataplexy precipitated by laughter is mistaken for a gelastic seizure.

Paroxysmal nocturnal dystonia presents as an often dramatic movement disorder from sleep with arousal and then vigorous motor activity, episodes typically lasting 30-60 s followed quickly by sleep [65]. They are usually amnestic for the episodes. Many patients originally diagnosed with this condition have since been recognized to have frontal lobe epilepsies. The diagnosis is made all the more difficult by movement artefact obscuring EEG traces made during the episodes.

Night terrors (pavor nocturnus) is a childhood parasomnia. Children wake from sleep screaming and crying inconsolably for many minutes, after which they go back to sleep and are amnestic for the episode. Rarely night terrors persist into adult life. If the diagnosis is in doubt, ictal EEG recordings can confirm that these do not have an epileptic basis [66].

Bruxism, or tooth grinding, can be a very striking nocturnal phenomenon. It is a benign disorder that requires no specific therapy.

Periodic movements of sleep are so distinctive that it is rare for them to be confused with seizures [67], They are characterized by repetitive flexion and extension, sometimes quite vigorously, of hip, knee, ankle and toe for a period of 30 s or so. The episodes frequently recur throughout the night troubling the bed partner but not the patient.

The REM behaviour disorders are much more complicated. These episodes occur from REM sleep and consist of the individual acting out components of dreams. Sometimes dramatic and prolonged, the activity can be complex, violent or aggressive and accompanied by agitation and vocalizations. Typically recurrent the attacks present a serious risk of injury for the partner. Causes include structural brain injury, such as subarachnoid haemorrhage. In some situations REM behaviour disorder might be difficult to distinguish from postictal confusion [68],

Although most parasomnias can be distinguished from epileptic disorders by their distinctive clinical features, polysomnography allows definitive diagnosis in most instances [69],

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