Narcolepsy is a neurological disorder that affects the control of sleep and wakefulness. People with narcolepsy experience excessive daytime sleepiness and intermittent, uncontrollable episodes of falling asleep during the daytime.
These sudden sleep attacks may occur during any type of activity at any time of the day.
In a typical sleep cycle, we initially enter the early stages of sleep followed by deeper sleep stages and ultimately (after about 90 minutes) rapid eye movement (REM) sleep. For people suffering from narcolepsy, REM sleep occurs almost immediately in the sleep cycle as well as periodically during the waking hours. It is in REM sleep that we can experience dreams and muscle paralysis which explains some of the symptoms of narcolepsy.
Narcolepsy usually begins between the ages of 15 and 25, but it can become apparent at any age. In many cases, narcolepsy is undiagnosed and, therefore, untreated.
What Causes Narcolepsy?
The cause of narcolepsy is not known; however, scientists have made progress toward identifying genes strongly associated with the disorder. These genes control the production of chemicals in the brain that may signal sleep and awake cycles. Some experts think narcolepsy may be due to a deficiency in the production of a chemical called hypocretin by the brain. In addition, researchers have discovered abnormalities in various parts of the brain involved in regulating REM sleep. These abnormalities apparently contribute to symptom development. According to experts, it is likely narcolepsy involves multiple factors that interact to cause neurological dysfunction and REM sleep disturbances.
What Are the Symptoms of Narcolepsy?
Symptoms of narcolepsy include:
- Excessive daytime sleepiness (EDS): In general, EDS interferes with normal activities on a daily basis, whether or not a person with narcolepsy has sufficient sleep at night. People with EDS report mental cloudiness, a lack of energy and concentration, memory lapses, a depressed mood, and/or extreme exhaustion.
- Cataplexy: This symptom consists of a sudden loss of muscle tone that leads to feelings of weakness and a loss of voluntary muscle control. It can cause symptoms ranging from slurred speech to total body collapse depending on the muscles involved and is often triggered by intense emotion, for example surprise, laughter, or anger.
- Hallucinations: Usually, these delusional experiences are vivid and frequently they are frightening. The content is primarily visual, but any of the other senses can be involved. These are called hypnagogic hallucinations when accompanying sleep onset and hypnopompic hallucinations when occurring during awakening.
- Sleep paralysis: This symptom involves the temporary inability to move or speak while falling asleep or waking up. These episodes are generally brief lasting a few seconds to several minutes. After episodes end, people rapidly recover their full capacity to move and speak.
How Is Narcolepsy Diagnosed?
A physical exam and exhaustive medical history are essential for proper diagnosis of narcolepsy. However, none of the major symptoms is exclusive to narcolepsy. Several specialized tests, which can be performed in a sleep disorders clinic or sleep lab, usually are required before a diagnosis can be established. Two tests that are considered essential in confirming a diagnosis of narcolepsy are the polysomnogram (PSG) and the multiple sleep latency test (MSLT).