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Narcolepsy is a chronic, neurological sleep disorder with no known cause. It involves the body's central nervous system. Narcolepsy is a genetic disorder, and is caused by a deficiency in the production of a neuropeptide (known as hypocretin or orexin) by a part of the brain called the hypothalamus.
The main characteristic of narcolepsy is excessive and overwhelming daytime sleepiness, even after adequate nighttime sleep. A person with narcolepsy is likely to become drowsy or to fall asleep at inappropriate times and places, and sleep attacks may occur with or without warning.
Attacks can occur repeatedly in a single day, drowsiness may persist for prolonged periods of time, and nighttime sleep may be fragmented with frequent awakenings.
The following are the most common symptoms of narcolepsy. However, individuals may experience symptoms differently. Symptoms may include:
- Excessive daytime sleepiness (EDS). An overwhelming desire to sleep at inappropriate times.
- Cataplexy. A sudden loss of muscle control ranging from slight weakness to total collapse.
- Sleep paralysis. Being unable to talk or move for about 1 minute when falling asleep or waking up.
- Hypnagogic and hypnopompic hallucinations. Vivid and often scary dreams and sounds reported when falling asleep (hypnagogic) or on awakening (hypnopompic).
Secondary or auxiliary symptoms include:
- Automatic behavior. Performing routine tasks without conscious awareness of doing so, and often without memory of it.
- Disrupted nighttime sleep, including multiple arousals
- Dream-enacting behaviors, in which patients may act out their dreams
Other difficulties may result from one's continuing struggle to cope, including:
- Feelings of intense fatigue and continual lack of energy
- Difficulty in concent
- rating and memorizing
- Vision (focusing) problems
- Eating binges
- Weak limbs
- Difficulties in handling alcohol
A combination of EDS and cataplexy provide for a preliminary clinical diagnosis.
In addition to a complete medical history and physical examination, laboratory tests to confirm diagnosis and plan treatment may include:
- Overnight polysomnogram (PSG). A sleep test to monitor various parameters during an entire night of sleep. This is to evaluate for other possible contributing sleep-related disorders.
- Multiple Sleep Latency Test (MSLT). Measures sleep onset and how quickly rapid eye movement (REM) sleep occurs during 5 naps. A mean sleep latency on the 5 naps of 8 minutes or less, in conjunction with 2 or more sleep-onset REM periods, is considered diagnostic of narcolepsy.
- Cerebral Spinal Fluid (CSF) hypocretin levels. A spinal tap for CSF to evaluate for possible hypocretin deficiency is used when there is concern about the possible diagnosis and other testing is either not possible or negative.
Genetic testing is no longer used because the human leukocyte antigen (HLA) markers may be negative in patients with narcolepsy and/or may be positive in patients who do not have narcolepsy. However, a link between reduced HLA markers and T cells, which are vital in the body's immune system, continued to be studied.