Differentials
seizures (sleep related)
SIGNS / SYMPTOMS
Sleep-related hypermotor seizures may be accompanied by incontinence, tongue biting, tonic-clonic movements, and drooling; these symptoms are not noted in the parasomnias.
Seizures may also occur when the patient is awake and asleep; parasomnias are always related to sleep.[59]
INVESTIGATIONS
An electroencephalogram may show abnormal electrical activity supporting a diagnosis of epilepsy.[56]
narcolepsy
SIGNS / SYMPTOMS
May present with similar features to recurrent isolated sleep paralysis.
In addition to daytime sleepiness, narcolepsy patients may have other symptoms including cataplexy (sudden focal or generalised loss of tone in the body associated with strong emotional experiences), hallucinations at sleep onset or on awakening.
INVESTIGATIONS
A multiple sleep latency test (MSLT) following an overnight polysomnogram differentiates narcolepsy from recurrent isolated sleep paralysis.
In an MSLT, patients are monitored in the sleep laboratory while having the opportunity to nap.
A short sleep latency (<8 minutes) and ≥2 sleep-onset rapid eye movement episodes with these naps indicate a diagnosis of narcolepsy.[60]
nocturnal dissociative disorder
SIGNS / SYMPTOMS
Often have underlying psychopathology.[61] The condition is identical to dissociative disorders occurring during the awake state, which result in the disruption of the integrated function of consciousness, memory, identity, or perception of the environment.[1]
Bizarre behaviour and experiences, such as pelvic thrusting, may be reported by eyewitnesses.[48] Examination may reveal evidence of previous self-harm, such as wrist cut marks or self-mutilation.[48]
INVESTIGATIONS
Structured clinical interview.
Polysomnography (PSG) is not required unless the clinical presentation is very atypical and cannot be differentiated clinically from rapid eye movement sleep behaviour disorder, sleepwalking, or sleep terrors. PSG reveals that the behaviour associated with the disorder emerges from an awake state, which was indicated on the electroencephalogram.[48][62]
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