Narcolepsy

On this page

Intro & Epi - Sleepy Spells Saga

  • Definition: Chronic neurological disorder marked by excessive daytime sleepiness (EDS) & REM sleep dysregulation.
  • Types:
    • NT1: With cataplexy or ↓ CSF hypocretin-1 levels.
    • NT2: Without cataplexy, and normal CSF hypocretin-1.
  • Epidemiology:
    • Prevalence: Approx. 20-60 per 100,000.
    • Onset: Typically adolescence/young adulthood (bimodal peaks).
  • Etiology (NT1):
    • Deficiency of hypocretin (orexin) from autoimmune destruction of hypothalamic neurons.
    • Genetic predisposition: HLA-DQB1*06:02.

⭐ NT1 is characterized by cataplexy or low CSF hypocretin-1 levels.

Pathophysiology - Orexin's Off Switch

  • Hypocretin (Orexin) Deficiency:
    • Orexin, a key neurotransmitter for wakefulness, is produced in the lateral hypothalamus.
    • In Narcolepsy Type 1 (NT1), there's a significant loss (>90%) of these orexin-producing neurons.
  • Autoimmune Basis:
    • Strongly associated with HLA-DQB1*06:02.
    • Believed to be autoimmune; potential triggers include infections (e.g., H1N1 influenza) via molecular mimicry, leading to neuronal loss.
  • REM Sleep Dysregulation:
    • Results in REM sleep elements intruding into wakefulness (e.g., cataplexy, sleep paralysis, hypnagogic/hypnopompic hallucinations).

Orexin neuron loss in narcolepsy vs. normal brain

⭐ The strongest genetic association for narcolepsy with cataplexy is HLA-DQB1*06:02.

Clinical Features - Attack of the Zzzzs

Classic tetrad (or pentad) of symptoms:

SymptomDescription
CataplexyPathognomonic (NT1); sudden loss of muscle tone (emotion-triggered); conscious.
Hallucinations (Hypnagogic/pompic)Vivid, dream-like experiences (sleep onset/awakening).
EDS (Excessive Daytime Sleepiness)First symptom; irresistible sleep urge; naps refreshing.
Sleep ParalysisTemporary inability to move/speak (sleep onset/awakening).
Sleep disruption (Nocturnal)(Pentad) Fragmented night sleep.

⭐ Cataplexy, a sudden loss of muscle tone triggered by emotions, is highly specific for Narcolepsy Type 1.

  • Other features: Automatic behaviors, obesity.## Clinical Features - Attack of the Zzzzs Classic tetrad (or pentad) of symptoms:

(table)[2a93bb7d-9125-47f5-b789-3b2d656e5769]📌 CHESS (Cataplexy, Hallucinations, EDS, Sleep Paralysis, Sleep disruption).

⭐ Cataplexy, a sudden loss of muscle tone triggered by emotions, is highly specific for Narcolepsy Type 1.

  • Other features: Automatic behaviors, obesity.

Diagnosis - Nailing Narcolepsy

  • Clinical Dx: History of Excessive Daytime Sleepiness (EDS) for at least 3 months PLUS one of:
    • Cataplexy AND a positive Multiple Sleep Latency Test (MSLT).
    • Cerebrospinal Fluid (CSF) hypocretin-1 concentration ≤ 110 pg/mL (or <1/3 of mean control values).
  • Polysomnography (PSG): Overnight sleep study. Essential to rule out other sleep disorders (e.g., Obstructive Sleep Apnea - OSA). May show reduced sleep efficiency, increased awakenings, or short REM latency.
  • Multiple Sleep Latency Test (MSLT): Objective measure of EDS, performed the day after PSG.
    • Mean sleep latency ≤ 8 minutes.
    • 2 Sleep-Onset REM Periods (SOREMPs) (one SOREMP can be from the preceding PSG).
  • CSF Hypocretin-1 Levels: Low levels (≤ 110 pg/mL) are diagnostic for Narcolepsy Type 1 (NT1). Invasive, thus not routinely performed if cataplexy is typical and MSLT is positive.

⭐ Diagnostic criteria for narcolepsy on MSLT include a mean sleep latency of ≤8 minutes and ≥2 SOREMPs.

MSLT Hypnogram with SOREMPs in Narcolepsy

Management - Wake-Up Call

Goals: Manage EDS, control cataplexy, improve quality of life.

  • Non-Pharmacological: Sleep hygiene, scheduled naps (15-20 min), regular sleep schedule, patient education.
  • Pharmacological:
    DrugTarget Symptom(s)Key Side Effects
    Modafinil/ArmodafinilEDS (1st line)Headache, nausea, anxiety
    MethylphenidateEDS (2nd line)Insomnia, irritability
    Sodium OxybateEDS, CataplexyNausea, dizziness, confusion
    TCAs/SSRIs/SNRIsCataplexy, REM symptomsAnticholinergic, GI upset
    PitolisantEDS, CataplexyHeadache, insomnia

⭐ Sodium oxybate is uniquely effective for treating both excessive daytime sleepiness and cataplexy in narcolepsy.

High‑Yield Points - ⚡ Biggest Takeaways

  • Excessive Daytime Sleepiness (EDS) is the primary and most persistent symptom.
  • Cataplexy, a sudden loss of muscle tone triggered by strong emotions, is highly specific.
  • The classic tetrad includes EDS, cataplexy, hypnagogic/hypnopompic hallucinations, and sleep paralysis.
  • Pathophysiology involves loss of orexin (hypocretin)-producing neurons in the hypothalamus.
  • Diagnosis: MSLT shows mean sleep latency ≤ 8 minutes & ≥ 2 SOREMPs.
  • Management: Modafinil for EDS; sodium oxybate, SSRIs/SNRIs for cataplexy.

Practice Questions: Narcolepsy

Test your understanding with these related questions

Child wakes up at night sweating and terrified, does not remember the episode - diagnosis?

1 of 5

Flashcards: Narcolepsy

1/10

Periodic limb movement disorders and atypical parasomnias can be diagnosed using _____

TAP TO REVEAL ANSWER

Periodic limb movement disorders and atypical parasomnias can be diagnosed using _____

polysomnography

browseSpaceflip

Enjoying this lesson?

Get full access to all lessons, practice questions, and more.

Start Your Free Trial