In the United States, it is estimated that narcolepsy, a rare sleep disorder, affects between 135,000 and 200,000 people, which is about 1 in every 2,000 people. Some experts believe only 25 percent of people with narcolepsy have been diagnosed with the condition. At the same time, many other sleep disorders, such as sleep apnea, restless legs syndrome, or even medication use, can lead to excessive daytime sleepiness. These can be mistaken for narcolepsy, as they share this primary symptom. Narcolepsy is a chronic neurological disorder, which is typically characterized by these symptoms:
There are two main types of narcolepsy and a very rare form of secondary narcolepsy.
Type 1 narcolepsy was previously known as narcolepsy with cataplexy. Along with EDS symptoms of the disease, the condition is characterized by either — or both — cataplexy or deficient levels of hypocretin, also known as orexin. Hypocretin is a neurotransmitter, a chemical produced by neurons, located in the hypothalamic region of the brain.
Type 2 narcolepsy, previously called narcolepsy without cataplexy, generally has less severe symptoms than type 1 narcolepsy. People with type 2 narcolepsy have excessive sleepiness and normal (or a small loss of) hypocretin levels. They do not experience cataplexy.
Secondary narcolepsy can develop due to an injury, tumor, or underlying condition that damages the hypothalamic region of the brain. People with secondary narcolepsy experience the typical narcolepsy symptoms but may also have severe neurological problems. They can require even greater amounts of sleep (more than 10 hours per night).
Type 1 narcolepsy is rarer than type 2. The rate of type 1 narcolepsy is about 14 out of 100,000 people. Type 2 narcolepsy occurs at a rate of approximately 65 out of 100,000 people. Some individuals who are initially diagnosed with type 2 narcolepsy may develop cataplexy as the disease progresses.
Narcolepsy can be difficult to identify because sleeping disorders often occur with other psychological and neurological conditions. Narcolepsy can be formally diagnosed through an analysis of sleep patterns and sleep/wake cycles that require an overnight stay in a sleep study center. There is usually the addition of a daytime sleep study following the overnight stay. A definitive diagnosis of narcolepsy can take an average of 15 years because symptoms can develop slowly over time and can be associated with many other conditions. The standard methods that determine a diagnosis include:
Narcolepsy can resemble sleep disorders with similar symptoms. According to one study of 41 people, almost 50 percent of individuals originally diagnosed with narcolepsy had been misdiagnosed. These people were later found to have other conditions such as obstructive sleep apnea, depression, irregular sleep cycles, and parasomnia. Sleepiness, loss of muscle control and muscle weakness, and immune system disorders can resemble narcolepsy.
Narcolepsy is also frequently underdiagnosed. One study showed that more than 61 percent of narcolepsy cases were incorrectly diagnosed as other conditions before a correct diagnosis was made. Because the condition is so rare, some primary care doctors are not familiar with the particular characteristics of narcolepsy. Underdiagnosis happens when narcolepsy is mistaken for anemia, vitamin deficiency, burnout, poor sleep hygiene, epilepsy, and other conditions. In particular, underdiagnosis can occur when someone does not present with all of the defining symptoms of narcolepsy.
Narcolepsy is likely caused by genetic and environmental factors. Viral and bacterial infections may trigger the onset of narcolepsy, as well as exposure to toxic substances. Narcolepsy mostly occurs without any family history of the disorder, although the condition can also run in families. People who have a parent, sibling, or child with type 1 narcolepsy are 40 times more likely to develop the condition.
According to one study with 109 people (68 women), women were diagnosed with narcolepsy less frequently than men, despite presenting with similar symptoms. The study determined that women were not as likely to report how their narcolepsy experiences impaired normal activities. Women were likely to be diagnosed with the condition 28 years after symptom onset. In comparison, men were diagnosed 16 years after first experiencing symptoms. The delay in diagnosis may affect how women with narcolepsy have been assessed compared to men.
The onset of narcolepsy can begin at any age, including early childhood. Most cases first occur between the ages of 10 and 30. The condition can have a sudden onset or appear more gradually.
In one study of 321 people that evaluated narcolepsy symptoms among different age groups, findings showed that for most people, daytime sleepiness and cataplexy were first experienced between the ages of 15 and 19 years. The onset of sleep paralysis and hallucinations first began between the ages of 20 and 24 years. Nonetheless, the condition can begin much later in life. Throughout the disease course, young and old people with narcolepsy were found to have comparable rates of cataplexy, sleep paralysis, and hypnagogic hallucinations.
Studies have shown that narcolepsy has similar symptoms across different ethnic groups in the United States. Limited studies have shown that African Americans have a higher prevalence of narcolepsy, particularly without cataplexy. The presence of the gene variation HLA-DQB1*06:02 is associated with a higher risk of narcolepsy. This variation has been found to differ significantly among various ethnic groups. In one study of people diagnosed with narcolepsy, the gene variation was found in 39.4 percent of African Americans, 23.8 percent of white people, 16.1 percent of Latinos, and 8.8 percent of Asians. African Americans were also found to have low levels of hypocretin in cases of type 2 narcolepsy without cataplexy.
Around the world, epidemiological studies that track the incidence and distribution of narcolepsy are limited. It is estimated that narcolepsy occurs at a rate that generally falls between 0.02 and 0.067 percent of the general population in the United States, Europe, Asia, and the Middle East. Notable exceptions are Japan, where the rates were found to be much higher at approximately 0.17 percent, and the Israeli Jewish population, where the prevalence of narcolepsy was found to be much lower at 0.002 percent.
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