Narcolepsy

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).

⭐ 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:

⭐ 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.

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:

  Drug	Target Symptom(s)	Key Side Effects
  Modafinil/Armodafinil	EDS (1st line)	Headache, nausea, anxiety
  Methylphenidate	EDS (2nd line)	Insomnia, irritability
  Sodium Oxybate	EDS, Cataplexy	Nausea, dizziness, confusion
  TCAs/SSRIs/SNRIs	Cataplexy, REM symptoms	Anticholinergic, GI upset
  Pitolisant	EDS, Cataplexy	Headache, 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.