Tests for narcolepsy can be performed by a qualified sleep specialist. During the appointment your doctor will ask questions about your symptoms, when, and how they developed. The doctor will ask you about sleepiness, possible episodes of cataplexy, your nighttime sleep patterns, and other symptoms like hallucinations, dreams, and sleep paralysis. At the same time, the doctor will rule out other causes of sleepiness and investigate other health conditions that may be causing your symptoms. The doctor may also do a physical exam.
If your symptoms sound like narcolepsy, the next step will be to collect more information about your sleep to confirm the diagnosis. For example,
- Overnight sleep study (polysomnogram). This is a are non-invasive, overnight study, conducted in a hospital or sleep center in which your sleep is monitored. While you sleep, an EEG monitors your brain waves and this information helps doctors understand what is causing your symptoms. Measurements of body movements, eye movements, heart and breathing rates, and oxygen levels are also taken throughout the night.
Home sleep tests (those that are performed at home versus in a sleep center) are used when a doctor suspects that abnormal breathing, such as apnea, is causing sleep disturbance or daytime sleepiness. Home sleep tests are not meant to diagnose other sleep disorders.
- Multiple Sleep Latency Test (MSLT). This is a daytime test conducted after an overnight sleep study so that your doctor can examine the quality of your nighttime sleep and the degree of sleepiness during the day. In the MSLT, you are asked to nap at five scheduled times at 2-hour intervals beginning a couple of hours after you wake up in the morning. How quickly you fall asleep and the type of sleep you have when you nap will be evaluated. Falling asleep quickly and entering rapid eye movement (REM) sleep during naps is one indication of narcolepsy. In preparation for this test, it’s important to follow your doctor’s instructions, because many factors can interfere with the results. For example, your doctor may recommend not taking certain medications—such as antidepressants, stimulants, or other medications affecting mood and behavior—for a period of time before the test.
- HLA typing.Many people with narcolepsy have a particular genetic marker related to the immune system. Testing for this genetic marker can be informative, but it is not a definitive test for narcolepsy, since some people without narcolepsy also have the marker.
- Hypocretin level test.The chemical hypocretin (deficient in many cases of narcolepsy) can be measured in cerebrospinal fluid. Talk to your doctor about whether this test is indicated.