What is Narcolepsy?
Narcolepsy is a chronic disorder of the central nervous system characterized by the brain’s inability to control sleep-wake cycles. At various times throughout the day, people with narcolepsy experience irresistible and sudden bouts of sleep, which can last from a few seconds to several minutes.
In narcolepsy, sleep episodes can occur at any time. People may unwillingly fall asleep while at work or at school, when having a conversation, playing a game, eating a meal, or, most dangerously, when driving an automobile or operating other types of machinery.
In addition to daytime sleepiness, other major symptoms include cataplexy (a sudden loss of voluntary muscle tone that may be triggered by strong emotions), vivid dream-like images or hallucinations during sleep onset or when waking, and brief episodes of total paralysis, also during sleep onset or when waking. The loss of muscle tone in cataplexy and sleep paralysis involves the simultaneous loss of both extensor reflexes (such as a knee tap and resulting leg jerk) and flexor reflexes (such as lifting the foot and/or leg following a foot prick or stepping on a sharp object). Normally, this kind of reflex loss exists only during REM sleep.
The diagnosis of narcolepsy involves a consultation and discussion about symptoms and review of one’s sleep history. Sleep studies are performed to measure how rapidly someone can fall sleep during daytime naps. In addition, we look for dreaming or REM sleep during these naps, strengthening the diagnosis. Blood tests suggest the diagnosis but are not definitive. Narcolepsy can be seen in other family members as well.
What Treatments are Available?
Narcolepsy cannot yet be cured. When cataplexy is present, the loss of hypocretin is believed to be irreversible and lifelong. But EDS and cataplexy can be controlled in most individuals with drug treatment. Modafinil and sodium oxybate are two drugs that have been approved by the U.S. Food and Drug Administration for the treatment of narcolepsy.
Doctors prescribe central nervous system alerting agents such as modafinil and amphetamine-like stimulants such as methylphenidate to alleviate EDS and reduce the incidence of sleep attacks. For most people these medications are generally quite effective at reducing daytime drowsiness and improving levels of alertness. However, these medications may be associated with several undesirable side effects so their use must be carefully monitored. Common side effects include irritability and nervousness, shakiness, disturbances in heart rhythm, stomach upset, nighttime sleep disruption, and anorexia. Individuals may also develop tolerance with long-term use, leading to the need for increased dosages to maintain effectiveness. In addition, doctors should be careful when prescribing these drugs and people should be careful using them because the potential for abuse is high with any amphetamine.
Two classes of antidepressant drugs have proved effective in controlling cataplexy in many individuals: tricyclics (including imipramine, desipramine, clomipramine, and protriptyline) and selective serotonin and noradrenergic reuptake inhibitors (including venlafaxine, fluoxetine and atomoxetine). In general, antidepressants produce fewer adverse effects than do amphetamines. But troublesome side effects still occur in some individuals, including impotence, high blood pressure, and heart rhythm irregularities.
In addition to central nervous system alerting agents and antidepressants, sodium oxybate or gamma hydroxybutyrate, also known as GHB or Xyrem®, can be used to treat narcolepsy. Sodium oxybate is a strong sedative that must be taken during the night. Sodium oxybate induces sleep and reduces the symptoms of daytime sleepiness and cataplexy. Due to safety concerns associated with the use of this drug, the distribution of sodium oxybate is tightly restricted.