How is Narcolepsy Diagnosed?
Narcolepsy is not definitively diagnosed in most patients until 10 to 15 years after the first symptoms appear. This unusually long lag-time is due to several factors, including the disorder's subtle onset and the variability of symptoms. As important, however, is the fact that the public is largely unfamiliar with the disorder, as are many health professionals. When symptoms initially develop, people often do not recognize that they are experiencing the onset of a distinct neurological disorder and thus fail to seek medical treatment.
A clinical examination and exhaustive medical history are essential for diagnosis and treatment. However, none of the major symptoms is exclusive to narcolepsy. EDS-the most common of all narcoleptic symptoms-can result from a wide range of medical conditions, including other sleep disorders such as sleep apnea, various viral or bacterial infections, mood disorders such as Depression, and painful chronic illnesses such as congestive heart failure and rheumatoid Arthritis that disrupt normal sleep patterns. Various medications can also lead to EDS, as can consumption of caffeine, alcohol, and nicotine. Finally, sleep deprivation has become one of the most common causes of EDS among Americans.
This lack of specificity greatly increases the difficulty of arriving at an accurate diagnosis based on a consideration of symptoms alone. Thus, a battery of specialized tests, which can be performed in a sleep disorders clinic, is usually required before a diagnosis can be established.
Two tests in particular are considered essential in confirming a diagnosis of narcolepsy: the polysomnogram (PSG) and the multiple sleep latency test (MSLT). The PSG is an overnight test that takes continuous multiple measurements while a patient is asleep to document abnormalities in the sleep cycle. It records heart and respiratory rates, electrical activity in the brain through electroencephalography (EEG), and nerve activity in muscles through Electromyography (EMG). A PSG can help reveal whether REM sleep occurs at abnormal times in the sleep cycle and can eliminate the possibility that an individual's symptoms result from another condition.
The MSLT is performed during the day to measure a person's tendency to fall asleep and to determine whether isolated elements of REM sleep intrude at inappropriate times during the waking hours. As part of the test, an individual is asked to take four or five short naps usually scheduled 2 hours apart over the course of a day. As the name suggests, the sleep latency test measures the amount of time it takes for a person to fall asleep. Because sleep latency periods are normally 10 minutes or longer, a latency period of 5 minutes or less is considered suggestive of narcolepsy. The MSLT also measures heart and respiratory rates, records nerve activity in muscles, and pinpoints the occurrence of abnormally timed REM episodes through EEG recordings. If a person enters REM sleep either at the beginning or within a few minutes of sleep onset during at least two of the scheduled naps, this is also considered a positive indication of narcolepsy.
