cataplexy

Cataplexy is a sudden loss of muscle strength, most often set off by a strong emotion: laughter, fear, anger, stress or excitement. The National Institute of Neurological Disorders and Stroke describes attacks that range from the mild, a brief drooping of the eyelids or weakness in a few muscles, to a total collapse of the body in which a person cannot move, speak or keep their eyes open. An episode usually lasts from a few seconds to several minutes and then resolves on its own, after which the ability to move and speak returns quickly.

The feature that distinguishes cataplexy from fainting or from a seizure is that the person remains fully conscious throughout, even when unable to speak. That difference matters clinically, because cataplexy is sometimes mistaken for a seizure disorder. Attacks vary enormously between people: some have only one or two in a lifetime, while others have many in a single day. Cataplexy may appear weeks or even years after daytime sleepiness begins, and in about 10 percent of narcolepsy cases it is the first symptom to show.

Cataplexy is the symptom that separates the two forms of narcolepsy. Type 1, once called narcolepsy with cataplexy, is marked by its presence and by very low levels of orexin; type 2 usually lacks it and comes with normal orexin levels. Where cataplexy is present, the cause is most often the loss of the brain cells that produce orexin, which is why the symptom is treated as a signature of that underlying deficiency rather than as a problem of the muscles themselves.