A sudden, temporary period of muscle weakness in fully-conscious people is called cataplexy. It is one of a series of symptoms found in narcolepsy and it is the primary symptom of nearly three-quarters of the people affected by it. Cataplexy in the absence of narcolepsy is rare. Most often cataplexy is triggered by emotions such as laughing, crying, surprise, fear, etc, and even intense exercise. The cause is believed to be an autoimmune destruction of the neurotransmitter hypocretin in the brain that regulates wakefulness .
Usually cataplexy presents first in teens and young adults with two peaks at 15 and 35 years of age, however it can be diagnosed in very young or older people, including those past the age of forty. Most commonly it presents with sagging jaw and head plus drooping shoulders. More severe cases often show transient weakness at the knees. Slurred speech may be present. One syndrome involves facial muscles exclusively .
Cataplexy occurs most frequently at times of stress, either emotional or when tired and deprived of sleep. In general, the severity of symptoms decreases with age but significant emotional upset, eg. loss of a spouse, can bring about severe attacks again. Most attacks last less than two minutes, a few last up to five minutes but rarely do they last longer than five minutes. Status cataplecticus occurs when repeated attacks recur rapidly, the "limp man syndrome". This is extremely disabling for the individual but is very rare.
There is often considerable delay between the onset of catalepsy and a specific diagnosis because of the lack of specific diagnostic tests.
A history of cataplexy in patients with EDS suggests a diagnosis of narcolepsy. In such patients, nocturnal polysomnography followed by multiple sleep latency testing can be confirmatory under the following conditions:
The maintenance of wakefulness test does not help with diagnosis but does help monitor treatment efficacy . Tests for other disorders that can cause cataplexy are usually indicated by the clinical history and physical examination. These include:
Hypnosis and other techniques of energy medicine, eg. Reiki, have been used with some success. Medical treatment targets cholinergic and noradrenergic neurotransmitter systems. Widely used tricyclic antidepressants (eg. clomipramine, imipramine, orprotriptyline and venlafaxine) inhibit the reuptake of norepinephrine and serotonin at nerve endings. However their potential adverse side-effects have led to their replacement by selective serotonin reuptake inhibitors (SSRIs), eg. fluoxetine, paroxetine, sertraline and citalopram. Serotonin reuptake inhibitors (SSRIs) can be used by all ages of patient with fewer side effects .
However both tricyclic antidepressants and SSRIs may cause REM behaviour disorder (RBD) with disturbance of normal REM sleep. They decrease the REM stage of sleep and its associated muscle atonia. As a result, patients may act out their dreams and cause harm to themselves or others.
Sodium oxybate (eg. xyrem) is being used for the treatment of cataplexy, although its mechanism is unknown . Hypocretin gene therapy and hypocretin cell transplantation are emerging for severe syndromes .
Almost all cases are transient and, apart from the few cases of secondary catalepsy, the severity of symptoms reduces over time, especially when patients adapt their behavior .
Within the brain, the hypothalamus regulates basic functions of hormone release, emotional expression and sleep. Patients with symptoms of cataplexy have reduced levels of hypocretin (also called orexin). Hypocretin, regulated by the hypothalamus, is critical in controlling sleep and levels of wakefulness; it also reflects reduced levels of histamine and epinephrine, chemicals that promote wakefulness, arousal and alertness.
The associated syndrome narcolepsy is known to be strongly associated with certain human leukocyte antigen (HLA) haplotypes. The offspring of such patients have a 40-fold increased likelihood of developing the condition. This suggests a probable genetic cause to the syndrome but, since occurrence in twins is low (25%), this suggests that environmental factors play an important part in triggering the disorder  .
It has been observed that the level of the neuropeptide hypocretin-1 is reduced in the cerebrospinal fluid of both narcoleptic animals and humans. This suggests that there may be an HLA-associated autoimmune destruction of hypocretin-containing neurons in the hypothalamus.
Sudden, short bouts of excessive daytime sleepiness (EDS) and hypersomnia are commonly seen with acute systemic disorders such as influenza and encephalitis. A range of underlying disease states may also induce cataplexy, EDS and/or hypersomnia:
Cataplexy can also be the result of ischaemic attacks, head injury and multiple sclerosis. Secondary cataplexy is caused by space-occupying lesions in the hypothalamus, usually the lateral or posterior lobes, that cause the level of hypocretin to fall. Lesions in the brain or brainstem are uncommon but could include arterio-venous abnormalities or neoplasia. Possible neoplasias include subependynoma, glioma, glioblastoma and astrocytoma. Rarely the syndrome can be the result of paraneoplastic syndromes (the indirect effect of neoplasias).
Iatrogenic cataplexy may also occur, transiently or permanently, due to lesions in the hypothalamus after surgery. The specific lesions or generalized disease or syndromes discussed above disrupt the hypocretin control in the hypothalamus in different ways.
It is recognised that many patients learn to avoid the emotions and situations which will trigger their attacks.
The muscular weakness of cataplexy can vary from slight loosening of facial muscles through to complete muscle paralysis of the whole body to the extent that the patients cannot maintain their posture. Most attacks are short and last between several seconds and a few minutes. The most frequent signs are the jaw dropping and neck weakness but weakness at the knees can be seen, alone or in conjunction with these signs. Slurred speech and impaired vision (eg. inability to focus or double vision) may be identified but hearing and alertness usually remain normal. Patients learn to recognize the slow development of a cataplectic attack, so serious injury from severe attacks is unlikely. Cataplexy attacks are self-limiting and generally resolve without the need for any medical intervention .
Cause: An autoimmune disease in a neurotransmitter, hypocretin, in the brain that regulates wakefulness is destroyed in most of the cases.
Diagnosis: Clinical signs are usually diagnostic but brain scans may be indicated to rule out underlying causes when the condition is deteriorating.
Treatment: Medical treatment is not usually necessary. Some success is claimed by hypnosis and other energy medicines. Effective drugs include tricyclic antidepressants and newer drugs such as the selective serotonin reuptake inhibitors (SSRIs).