Differential diagnosis of sleep laughter: A case report and literature review.

Sleep laughter is a relatively common phenomenon. It is classically seen during REM sleep, which is associated with dreams, and may be a component of REM sleep without atonia (RWA) as seen in cases of REM sleep behavior disorder (RBD). However, repetitive laughter episodes during NREM or during sleep-wake transition have not been described in the literature. We present a case of paroxysmal laughter out of drowsiness and NREM sleep, occurring almost every night, prompting evaluation for a possible seizure disorder. Multiple tests were unrevealing, including brain magnetic resonance imaging, polysomnogram, multiple sleep latency test and electroencephalogram. However, despite the lack of diagnostic certainty, this case provoked a discussion of key factors distinguishing parasomnia from seizure, which is useful for all physicians who may be faced with a case of unusual behavior in sleep. This case highlights the challenges that are encountered when trying to classify certain unusual sleep-related paroxysmal events.