During wakefulness, the pontine REM sleep centres are inhibited by noradrenaline and serotonin (5HT) released by activity in the locus coeuruleus and raphe nuclei, but in REM sleep and during cataplexy this inhibition ceases. This causes glycine-mediated inhibition of the alpha motor neurones in the spinal cord with loss of muscle activity. Emotional activity in the limbic system activates the pontine REM sleep centres and nearby regions to increase the activity in the medullary motor centres. The neurological mechanisms underlying cataplexy are complicated. Attention to sleep hygiene, particularly avoiding sleep deprivation, may help, but nevertheless most subjects require drug treatment, usually in the long term. Episodes can sometimes be aborted by tensing the muscles at the onset of an attack. Patients tend to avoid situations in which sudden or intense emotions may be felt and develop coping techniques of controlling the emotions in order to prevent cataplexy. Each episode usually lasts for a few seconds or up to two minutes.

It is a specific feature of narcolepsy, a condition characterised by fragmentation and instability of rapid eye movement (REM) sleep, such that the muscle atonia which is normal in REM sleep can appear during wakefulness.Ĭataplexy may be mild and only cause, for instance, twitching of the face or the upper limbs, but it can lead to generalised muscle weakness in which the subject falls to the ground. Cataplexy is the sudden onset of muscle weakness during wakefulness.(1) It is almost always triggered by sudden or intense emotion, usually laughter.

Cataplexy in narcolepsy