Makindo Medical Notes

Hypocretin 1 and 2 are hypothalamic factors of the incretin family involved in the sleep-wake cycle.

Fits of sleep by day
Yanked in, dreams won’t stay away
Low orexin A
Laughter prompts brief loss of tone
‘Wide awake’ is zone unknown
@DrCindyCooper

About

• Narcolepsy is a chronic neurological disorder that affects the regulation of the sleep/wake cycle in the brain.
• This disorder is characterized by disordered REM sleep regulation, leading to disrupted sleep patterns and excessive daytime sleepiness.

Classic Tetrad of Symptoms

• Excessive daytime sleepiness (EDS)
• Sleep paralysis
• Hypnagogic jerks and hallucinations
• Cataplexy (present in Narcolepsy Type 1)

Cataplexy, a hallmark of narcolepsy type 1, is triggered by strong emotional stimuli such as laughter, crying, or stress. It can manifest as slurred speech or, in more extreme cases, complete collapse. Despite the loss of muscle tone, the patient remains conscious throughout the episode, which typically lasts seconds to minutes.

Types of Narcolepsy

• Type 1: Characterized by loss of hypocretin in the brain and the presence of cataplexy.
• Type 2: No significant loss of hypocretin and no cataplexy.

Aetiology

• Cataplexy is caused by a deficiency of hypocretin (also known as orexin) cells in the hypothalamus.
• Orexin-A is a neuropeptide involved in the regulation of the sleep/wake cycle. Low levels of orexin-A in cerebrospinal fluid (CSF) are indicative of narcolepsy type 1.
• There is a high prevalence of the HLA-DQB1*0602 allele in narcolepsy patients. However, genetic testing for this allele is not recommended as up to 30% of the general population also carries it without having narcolepsy.

Clinical Features

• Excessive daytime sleepiness (EDS), which significantly impairs daily activities.
• Hypnagogic hallucinations: Vivid, often frightening, hallucinations experienced while falling asleep.
• Hypnopompic hallucinations: Hallucinations experienced while waking up.
• Cataplexy: Sudden loss of muscle tone triggered by emotions like laughter or surprise, causing collapse but without loss of consciousness.
• Sleep paralysis: A brief inability to move when falling asleep or waking up.
• Diagnosis is typically made using the Epworth Sleepiness Scale and confirmed with the Multiple Sleep Latency Test (MSLT).

Differential Diagnosis

• Sleep Apnoea: A common differential diagnosis due to shared symptoms of excessive daytime sleepiness.

Management

• Good Sleep Hygiene: Establishing regular sleep patterns and scheduling daytime naps is crucial for managing symptoms.
• Pharmacological options:
  • Modafinil: A wakefulness-promoting agent, often first-line treatment.
  • Sodium Oxybate: Effective for both cataplexy and excessive daytime sleepiness.
  • Dextroamphetamine: A stimulant that can help manage daytime sleepiness.

References

• Narcolepsy: A Clinical Review