What is narcolepsy?

Updated: Oct 09, 2018
  • Author: Sufen Chiu, MD, PhD; Chief Editor: Caroly Pataki, MD  more...
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Narcolepsy is defined by DSM-5 as recurrent periods of an irrepressible need to sleep, lapsing into sleep, or napping that occurs within the same day. This must occur 3 times per week over 3 months. It also requires one of the following to be present:

  • Episodes of cataplexy occurring a few times per month: Cataplexy is defined as (1) in individuals with chronic disease, as having brief (seconds to minutes) episodes of sudden loss of muscle tone with maintained consciousness that are triggered by laughter or joking or (2) in children or individuals within 6 months of onset, spontaneous grimaces or jaw-opening episodes with tongue thrusting or a global hypotonia without any obvious emotional precipitants.

In pediatric patients, excessive daytime sleepiness is the most common first symptom of narcolepsy. [5] Symptom onset peaks at 15 years of age. Low hypocretin levels are present, they must occur in the absence of acute brain injury, inflammation, or infection. Nocturnal sleep PSG shows REM sleep latency to be less than or equal to 15 minutes or a multiple sleep latency test shows a mean sleep latency of less than or equal to 8 minutes with 2 or more sleep-onset REM periods.

REM sleep mechanisms are dysregulated in youths with narcolepsy, but evidence also exists of non-REM (NREM) and circadian sleep-wake cycle abnormalities. REM-associated sleep phenomena intrude into the awakened state. Sleep attacks (sleep), cataplexy (abrupt atony precipitated by strong emotions), and hypnagogic and hypnopompic hallucinations (experienced as dreamlike events immediately before sleep onset or upon awakening) are characteristic of narcolepsy.

Excessive daytime somnolence leading to irresistible or involuntary sleep (sleep attacks) may occur. The roles of the neuropeptide hypocretin and human leukocyte antigen (HLA)-DR2/DBQ1 as a genetic-neuroimmune interaction are being considered in current research on this issue. Narcolepsy is consistent with the polygenic model of development in most human cases. Narcolepsy triggered by streptococcus infections, H1N1 influenza, and H1N1 vaccination in genetically vulnerable individuals has been reported. [5]

Specifiers include the following:

  • Narcolepsy Without Cataplexy But With Hypocretin Deficiency

  • Narcolepsy With Cataplexy But Without Hypocretin Deficiency

  • Autosomal Dominant Narcolepsy, Obesity, and Type 2 Diabetes

  • Narcolepsy Secondary to Another Medical Condition

Narcolepsy can be diagnosed even when secondary to infections, trauma, or tumor, such as in Whipple disease or sarcoidosis. There is destruction of hypocretin neurons. Individuals who are HLA DQB1*06.02 positive may be more vulnerable to destruction of these neurons from an autoimmune process. Transient decreases in cerebrospinal fluid (CSF) hypocretin levels can occur without cell loss and can complicate the diagnosis. Functional imaging has demonstrated impaired hypothalamic responses.

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