Complete and elaborate summary of the third task of the elective course PSY3349 - Sleep and sleep disorders. Summary contains all resources on the reference list, including figures.
Source: Van der Heide & Lammers in Thorpy & Billiard (2011)
According to the International Classification of Sleep Disorders, narcolepsy can be divided into
narcolepsy with and without cataplexy. Narcolepsy with cataplexy is considered to be a
homogeneous disease, of which the pathophysiological hallmark is a disturbed hypocretin
transmission. Narcolepsy without cataplexy may be no more than a heterogeneous group of disorders
characterised by excessive daytime sleepiness (EDS) in combination with abnormal expressions of
REM sleep on PSG. Most cases of narcolepsy without cataplexy do not develop cataplexy later on, so
it is not simple an early stage. Discusses below; narcolepsy with cataplexy.
Clinical features
Excessive daytime sleepiness
EDS is the leading symptom of narcolepsy, which is present in all patients and is usually the first
symptom. EDS is present daily. It is characterised by a inability to stay awake, and in the majority of
patients by an almost continuous feeling of sleepiness (dependent on the level of activity).
Monotonous activities such as watching tv, reading, attending a meeting or being passenger in a car
increase the feeling of sleepiness and increase the chance of a sleep attack. Conversely, intense activity
(physical or mental) decreases sleepiness. Sleep attacks tend to be short, usually less than 20 min, and
refreshing. The number of attacks may vary from 1 to over 10 each day.
EDS is typically accompanied by a pronounced difficulty to concentrate and to sustain attention,
leading to impaired performance. This expression of EDS may even cause more problems in
interpersonal relationships than the sleep attacks. EDS severely reduces quality of life.
Cataplexy
Cataplexy is characterized by a sudden bilateral loss of muscle tone, with preserved consciousness,
elicited by emotions. All striated muscles can be involved. Notable exceptions are eye muscles and
muscles involved in respiration. Cataplexy may be ‘complete’, indicating loss of muscle tone in all
muscles. Muscle twitches and jerky movements may be part of the attack. Complete attacks may
cause falls. Since it takes several seconds for a complete attack to build up, most patients are able to
take countermeasures (e.g. sitting).
Cataplexy is most often provoked by an emotional trigger; rather than the actual emotion, its
anticipation may trigger an attack. Common examples are not being able to tell the punchline of a
joke and not being able to score a goal during soccer. Another common trigger is an unexpected
meeting with an acquaintance.
Anger can also provoke attacks. A
degree of relaxation or comfort
with the situation may be
prerequisite, as uncomfortable or
stressful situations prevent their
occurrence.
,PSY3349 Sleep and Sleep Disorders
The frequency of attack varies from dozens a day to less than once a month. Most attacks last seconds
to half a minute, sometimes up to two minutes (rarely longer). Partial attacks tend to be shorter, the
majority even less than 10s. When the trigger remains present for minutes, repeated attacks may occur,
giving the impression of a very long-lasting single attack. Cataplexy is the only truly specific feature
of narcolepsy, but it is the first symptom to appear in less than 10%.
Hypnagogic hallucinations
Hypnagogic hallucinations (HH) are very vivid, dreamlike experiences that occur during the
transition from wakening to sleep. The content of the hallucination varies, but in general they are
extremely unpleasant and frightening. In 85% of the hallucinations multiple senses are
simultaneously involved. Examples are that someone the know seems to enter that room, or patients
may hallucinate that they are undergoing surgery without anesthesia in their own bed. Often, HH
appear so realistic that patients have difficulty telling them apart from real events after waking up.
Their occurrence during the transition between wakefulness and sleep also helps the diagnosis, as
hallucinations in psychiatric disorders can occur at any moment. There is no reason to think that HH
point towards a psychotic disorder; psychotic disorders do not occur more often in narcolepsy. HH are
not specific for narcolepsy, since they are also present in the general population and other sleep
disorders.
Sleep paralysis
Sleep paralysis is the inability to move at awakening or when falling asleep while being
subjectively awake and conscious. The paralysis may be complete (not being able to move a single
muscle). Attacks last up to several minutes. Sleep paralysis has similarities with both cataplexy and
HH; the timing resembles that of HH, whereas the pattern of affected muscles resembles that of
complete attacks of cataplexy. Sleep paralysis may occur simultaneously with HH. It occurs as a
symptom of its own and is therefore not specific for narcolepsy.
Disturbed nocturnal sleep
Sleep latency in narcolepsy is very short; patients typically fall asleep as soon as they lie down. They
do not stay asleep, which is reflected in frequent awakenings, of which most are brief but some last
for more than one hour. The total duration of nocturnal sleep is by and large comparable to the
situation before. Remarkably, there is no clear correlation between the severity of EDS and the extent
of disturbed nocturnal sleep.
Associated symptoms
There are some other features frequently present that may be related to the inability to sustain
attention. One of them is automatic behavior; the performance of semi-purposeful, inadequate
daytime activity, for example, driving to a certain place by car without knowing how and why they did
so. Memory complaints occur frequently, which might be explained by other factors than temporary
lapses in attention. A final symptom, not directly related to impaired sustained attention, is obesity.
About 30% of patient have a BMI of at least 30kg/m2. Obesity may be explained in part by decreased
activity or increased caloric intake, but may be a direct consequence of hypocretin deficiency.
, PSY3349 Sleep and Sleep Disorders
Comorbidities
Sleep apnea and parasomnias are frequently present, but at an unknown frequency. One study
reported the presence of obstructive sleep apnea in 25% of patients. Periodic limb movements in
sleep (PLMS) have been described in up to two-thirds of patients. REM sleep behavior disorders
(RBD) has a significantly higher prevalence compared to the general population, affecting 12-36% of
patients. It can be difficult to diagnose depression as a comorbid disorder, but depression is
considered to have a higher prevalence in narcoleptics than in the general population; 5-30%.
Diagnosis
Figure; criteria for narcolepsy with cataplexy
according to the ICSD. The presence of EDS
and cataplexy, both of which must be
evaluated by careful history-taking, is required,
and should be confirmed with
polysomnography studies including a
multiple sleep latency test (MSLT) and/or
hypocretin-1 measurement in the CSF.
The sensitivity of low or absent hypocretin-1
levels in the CSF of patients suffering from
narcolepsy with cataplexy is about 90%.
Specificity is even higher. Hypocretin-1
measurement is more reliable for the
confirmation of narcolepsy than the MSLT
(sens. 71,5%, spec. 66%).
Differential diagnosis
EDS in combination with cataplexy is pathognomonic for narcolepsy with cataplexy. The only
relevant question in those cases is whether is concerns the idiopathic form (narcolepsy due to
medical condition). In the absence of cataplexy the diagnosis is more difficult, but can be made if the
patient meets the PSG criteria (table; narcolepsy without cataplexy).
However, it has been demonstrated that the
clinical as well as the MSLT findings can be
induced by chronic sleep deprivation; in
those cases, a low (or undetectable)
hypocretin-1 level can prove the diagnosis.
From a clinical point of view, the
differentiation from idiopathic hypersomnia
(IH) may also be difficult. In these cases, the
MSLT will sort them out by the presence of
fewer than two SOREMPs. Moreover,
hypocretin-1 levels are normal in IH.
Pathophysiology
The hypocretin system
The hypocretin system includes two peptides (hypocretin 1 and 2) and two receptors. Both hypocretin
peptides are cleaved from a common precursor (preprohypocretin) and have a different receptor
affinity profile. Hypocretin-1 has equal affinity for both receptors, while hypocretin-2 preferentially
binds to the hypocretin receptor-2. Hypocretins are produced by neurons in the dorsolateral
hypothalamus, centered around the fornix. Although the hypocretin cell bodies lie in a small area,
their axons project throughout the whole brain, except the cerebellum (figure).
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