Most people go through several stages of sleep before settling into a stage called REM (rapid eye motion) sleep. But narcoleptics often fast-forward through the other stages and reach REM sleep in mere minutes.
Symptoms of Narcolepsy
Narcolepsy can present itself in a variety of ways. No one symptom is enough to diagnose narcolepsy. The most common symptoms are:
- Excessive Daytime Sleepiness (EDS), or the urge to sleep at random times during the day, often despite getting a full night’s sleep, has led narcolepsy to be thought of as “irresistible sleep.” EDS is typically the first narcoleptic symptom to occur.
- Cataplexy, which is almost exclusive to narcoleptics, is a sudden bilateral paralysis of the muscles usually triggered by strong emotion. Cataplexy can be subtle and brief – a jaw sags or knees buckle for a few seconds – or it can be extreme and prolonged – collapse and total body paralysis for half an hour.
- Sleep paralysis is a temporary inability to move or talk upon waking. Sleep paralysis can be very frightening to experience, but should not be a cause for concern.
- Hypnogogic hallucinations, which can contain visual, auditory, and tactile elements, occur during transitional periods between sleep and wakefulness.
- Automatic behavior in narcoleptics may include acting out dreams or sleep walking.
Causes of Narcolepsy
The cause of narcolepsy is not yet fully understood. However, approximately 90% of narcoleptic humans have very low levels of a neurotransmitter known as hypocretin (Hcrt, also known as orexin). There seems to be an autoimmune issue involved: an allele called HLA-DQ1*0602 and some unknown trigger cause hypocretin neuron death. Typically, hypocretin neuron death happens slowly over time. (Narcoleptic dogs are missing these neurons altogether, but that is exceedingly rare in humans.) By affecting other neurotransmitters, low levels of Hcrt disrupt the body’s ability to regulate wakefulness.
Some people suffer from secondary narcolepsy; that is, brain trauma (from injury, cancer, or other causes) leads to hypocretin neuron death and causes narcolepsy as a side effect.
Diagnosing Narcolepsy
Because symptoms can be so varied and the progression of the disease is slow, diagnosis can take 10-15 years from the onset of the first symptom. According to the International Classification of Sleep Disorders (ICSD), presence of excessive daytime sleepiness and cataplexy is sufficient to confirm a diagnosis of narcolepsy. Otherwise, sleep tests are called for:
- Nocturnal polysomnograms (NPSGs) are used to rule out other causes of EDS. NPSGs can also spot early nocturnal REM onset, if present.
- A daytime sleep test, the Multiple Sleep Latency Test (MSLT), is used to determine how quickly patients falls asleep during daytime naps and whether they experience REM sleep. Sleep latency periods of less than 5 minutes and two or more early onsets of REM are indicative of narcolepsy.
Treatment of Narcolepsy
Currently, treatment of narcolepsy typically focuses on the symptoms, not the cause. Both medication and behavioral changes are recommended, particularly for excessive daytime sleepiness. CNS stimulants such as Modafinil are usually prescribed for EDS. Improving nocturnal sleep and taking regular daytime naps can also ease EDS. Sodium oxybate (Xyrem) is the only FDA-approved drug for cataplexy. Clinicians also prescribe medicines, such as heterocylclic antidepressants and selective serotonin reuptake inhibitors (SSRIs), off label.
In the past few years, much has been learned about what narcolepsy is and how it is caused. Researchers are hopeful that this will translate to more effective drugs in the near future.
