Cataplexy: cause, meaning, sleep, cure and etymology
Cataplexy is a generally temporary disorder that causes a loss of muscle tone usually triggered by strong emotions such as crying, laughter, joy, etc. and the memory of them, or occurs randomly during the course of the day
It can affect completely healthy people who have never had a seizure in their lives.
The word ‘cataplexy’ derives etymologically from the Greek κατάπληξις meaning ‘astonishment’.
Cataplexy can have different levels of severity:
- mild cataplexy: causes mild and temporary weakness in the subject with limb failure and generally lasts a few seconds;
- moderate cataplexy: causes partial weakness in the subject with limb failure and may last several minutes;
- severe cataplexy: there is complete muscular atonia that may last 30 minutes or more.
These disturbances are sudden, unpredictable and not anticipated by any premonitory signs and can therefore be dangerous if they occur while driving a motor vehicle or when performing dangerous work.
Generally, the patient finds himself as if paralysed and risks falling if he is standing at the time.
Cataplexy can last from a few seconds to about thirty minutes, during which time the patient remains fully conscious of what is happening.
In the most severe cases, fortunately rare, severe bradycardia (slowing of the heart rate) combined with bradypnoea (slowing of the respiratory rate) and arterial hypotension (lowering of the blood pressure) may occur during the attack, so much so that to the untrained eye the subject may even appear to be dead.
Causes of cataplexy
The causes of this disorder are unknown, although it is thought to be caused by a dysfunction of the sleep-wake functions: in fact, when this disorder occurs, the body feels as if it is sleeping while the mind is in a waking state.
Clinical experiments carried out in the 1990s by Jerome M. Siegel’s team on narcoleptic dogs showed that an unusual activity of the medulla oblongata was responsible for the cataplexy, while the University of Lyon demonstrated that damage in the upper regions of the brainstem that connect to the medulla oblongata affects the disease, as does another area of the brainstem called the locus coeruleus, whose cells become inactive before and during cataplexy and sleep.
According to these studies, there are two concomitant causes for the development of the disease: the lack of excitation of motor neurons caused by the suspension of noradrenal cells and the activation, instead, of the parallel system in the medulla that inhibits motor neurons.
At the same time, at Stanford University, Emmanuel Mignot’s research staff discovered that suffering dogs would be victims of a genetic mutation of the neurotransmitter orexin.
A third hypothesis was proposed by researchers at the Seiwa Hospital in Tokyo, who verified the link between cataplexy and certain as yet unknown environmental factors that trigger an autoimmune reaction, capable of damaging the neurons that regulate awakening and muscle tone.
Diagnosis of cataplexy
Cataplexy is rarely seen during an outpatient visit and the diagnosis can be made by a specialist who is familiar with the condition.
Measurement of hypocretin levels in the cerebrospinal fluid can confirm the diagnosis.
Treatment of cataplexy
Cataplexy is treated pharmacologically. The first product approved by the FDA for the treatment of cataplexy related to narcolepsy is Xyrem® (sodium oxybate).
Symptoms can be suppressed with the help of tricyclic antidepressants and serotonin reuptake inhibitors.
Despite its relation to narcolepsy, in the majority of cases, cataplexy must be treated separately.
Cataplexy, sleep and narcolepsy
When the patient suffers from both cataplexy and narcolepsy, one speaks of ‘Gélineau syndrome’ after the neurologist Jean-Baptiste-Édouard Gélineau, who first described it.
This syndrome is characterised by excessive daytime sleepiness, with brief bouts of sudden, irresistible sleepiness that interrupt normal activity, and the complete loss of muscle tone following emotional shocks.
Subjects affected by this disorder also report paralysis and hypnagogic hallucinations.
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