Narcolepsy with or without cataplexy


Narcolepsy is a neurological disorder that affects the natural cycles of sleeping and waking. It is characterized by excessive sleepiness during the day. This rare disease affects 2–5 out of every 10,000 people (1). At the present time nothing has been found to cure the disease. Therefore the treatment concentrates on relieving the symptoms as far as possible.

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Causes

Orexin is a natural hormone produced in our brain that helps us to stay awake (2-4). In most people with narcolepsy, the small region of their brain where orexin is produced is not working properly. Certain cells in this area are irreversibly damaged by an autoimmune process – that is, the patient's own immune system has attacked the cells in this brain region. The probability of this type of autoimmune reaction is partly inherited. Among people who have a genetic disposition towards this autoimmune condition, the risk of developing the disease may be increased by infections or by the vaccination against swine flu (5).

Changed sleep cycles

Healthy people sleep in cycles of about 90 minutes each. A normal sleep cycle includes phases with stable and deep sleep, followed by a phase with rapid eye movement (REM). In the REM phase, the person’s eyes move around quickly while their eyelids are closed, and this is the phase in which we have most of our dreams (6). 

In people with narcolepsy, the sleep cycles are disturbed. Instead of spending time in the “non-REM" phases of stable and deep sleep, patients go into REM phase shortly after falling asleep (7).

Symptoms 

The classic symptoms of narcolepsy include abnormal sleepiness during the day, disturbed sleep at night, hallucinations, sleep paralysis and cataplexy. The intensity of the symptoms can be very different from one patient to another, and some symptoms (e.g. cataplexy) may be completely absent (8).

Excessive sleepiness during daytime

The sleepiness during daytime is the central symptom of narcolepsy. Patients often describe it as irresistible and uncontrollable. They feel tired and lethargic during the day and may fall asleep suddenly. These naps are often very short, and the patients feel refreshed and more alert afterwards (7,9).

One consequence of daytime sleepiness may be ‘automatic behaviours’ in which patients continue activities being half-asleep - these actions may be executed with errors or purposeless (7). 

Disturbed sleep at night

A less well-known but common symptom of narcolepsy is disturbed sleep at night, in which patients wake up frequently (9). 

Sleep-related hallucinations

Narcolepsy patients often suffer from intense hallucinations while falling asleep or waking up. These can include seeing, hearing or touching things that don’t exist in reality but are often experienced as highly realistic. The hallucinations are mainly perceived as threatening or unpleasant (7).

Sleep paralysis

In healthy people sleep paralysis, which is the total inability to move, is normal during sleep and prevents them moving around while dreaming. Patients with narcolepsy, in contrast, often suffer from sleep paralysis at the beginning or end of sleep and they may consciously experience being paralysed. This could last from a few seconds to some minutes and can be a very frightening experience (7).

Cataplexy

Cataplexy is the term for a brief temporary loss of power in muscles. It ranges from mild cases, in which for example the facial muscles go limp, to severe forms, where a patient loses the strength to stay upright and drops. Episodes of cataplexy can be triggered by emotions such as laughing, anger or surprise and usually last only a few seconds (10).

 

1. Longstreth WT, Koepsell TD, Ton TG, Hendrickson AF, van Belle G. The epidemiology of narcolepsy. Sleep. 2007; 30 (1): 13-26

2. Nishino S, Ripley B, Overeem S, Lammers GJ, Mignot E. Hypocretin (orexin) deficiency in human narcolepsy. Lancet. 2000; 355 (9197): 39-40

3. Thannickal TC, Nienhuis R, Siegel JM. Localized loss of hypocretin (orexin) cells in narcolepsy without cataplexy. Sleep. 2009; 32 (8): 993-8

4. Thannickal TC, Moore RY, Nienhuis R, Ramanathan L, Gulyani S, Aldrich M, et al. Reduced number of hypocretin neurons in human narcolepsy. Neuron. 2000; 27 (3): 469-74

5. Bonvalet M, Ollila HM, Ambati A, Mignot E. Autoimmunity in narcolepsy. Curr Opin Pulm Med. 2017; 23 (6): 522-9

6. Rechtschaffen A, Kales A. Los Angeles: University of California, Brain Information Service/Brain Research Institute. 1968

7. Dauvilliers Y, Billiard M, Montplaisir J. Clinical aspects and pathophysiology of narcolepsy. Clin Neurophysiol. 2003; 114 (11): 2000-17

8. Deutsche Gesellschaft für Neurologie - Leitlinien Narkolepsie. 2012:https://www.dgn.org/images/red_leitlinien/LL_2012/pdf/030-056l_S1_Narkolepsie__verlaengert.pdf

9. Roth T, Dauvilliers Y, Mignot E, Montplaisir J, Paul J, Swick T, et al. Disrupted nighttime sleep in narcolepsy. J Clin Sleep Med. 2013;9 (9): 955-65.

10. Dauvilliers Y, Arnulf I, Mignot E. Narcolepsy with cataplexy. Lancet. 2007; 369 (9560): 499-511.