Narcolepsy is a sleep disorder marked by excessive daytime sleepiness (EDS), which can cause significant health consequences for children, teens, and adults.
As an uncommon disorder, narcolepsy may not be immediately recognized or suspected, which is why many cases are believed to be undiagnosed or only diagnosed many years after the start of symptoms. Unfortunately, delayed diagnosis can prevent patients from getting treatment that can improve their safety and quality of life.
Diagnosing narcolepsy is a multi-step process guided by a doctor that often involves various medical tests and sleep studies. Understanding this process can help individuals with symptoms of narcolepsy work with their doctor and know what to expect during appointments and tests.
In some cases, a referral may be made to a doctor who specializes in sleep medicine, a neurologist, and/or a psychiatrist to conduct additional evaluations that may aid in diagnosis and treatment.
Anyone who is concerned about excessive daytime sleepiness (EDS) or narcolepsy should start by talking with their primary care physician or family doctor. This first contact can initiate the diagnostic process, which involves several steps.
At the outset, the doctor needs to find out more about your symptoms, review your health history, and do a basic physical exam.
To better understand your symptoms, the doctor may ask questions like:
EDS can be caused by many conditions, and your answers to these questions provide valuable information that helps the doctor identify the most likely explanation. A physical exam and a review of your health history and current medications can also help rule out other causes of your symptoms.
To gather more information about your sleep, the doctor may ask you to take a short test called the Epworth Sleep Scale (ESS). Your subjective responses to these survey questions help the doctor quantify your sleepiness.
In addition, you may be asked to keep a sleep log, which is a diary of your sleep habits, for a week or more. Another way to measure your sleep is with actigraphy, which is a watch-like device that uses a tracker to monitor your movement.
While all of this information can be essential, narcolepsy cannot be diagnosed on the basis of symptoms alone. Instead, other tests must be conducted to discount other potential causes of symptoms and confirm a narcolepsy diagnosis.
If your doctor suspects that you may have narcolepsy or another sleep disorder, it’s common for them to recommend two specialized sleep studies:
Both PSG and MSLT are complex tests performed in a specialized sleep clinic. At-home testing is not an option for narcolepsy because it lacks the necessary monitoring of brain activity.
The results of the PSG and MSLT can be critical in diagnosing narcolepsy. People with both NT1 and NT2 tend to fall asleep in less than eight minutes on average, and they usually enter REM sleep much earlier than people without narcolepsy.
To ensure these tests produce valid results, it’s vital to prepare for them correctly. Preparation includes stabilizing your sleep schedule for at least a week beforehand, which may need to be documented by a sleep log or actigraphy. It’s also important to stop using medications or substances that could interfere with your sleep during the tests.
Your doctor or a technician at the sleep clinic can provide specific instructions and let you know what to expect before you go in for these sleep studies.
A lumbar puncture removes some cerebrospinal fluid (CSF) from the lower spine that can be tested for its levels of hypocretin. Also called orexin, hypocretin is a chemical that helps control sleep and wakefulness. Low levels are indicative of narcolepsy type 1, which involves the loss of neurons in the brain that produce hypocretin.
Along with low hypocretin levels, almost everyone with NT1 carries a variation in a gene called HLA-DQB1*06:02. Human leukocyte antigen (HLA) testing can look for this variation, but, because it exists in many people without narcolepsy, it alone is not capable of providing a diagnosis.
Though not routine, other medical tests, such as blood work or imaging tests, may be recommended by the doctor if they suspect and want to test for another condition that may be causing your symptoms.
Taking all of the information — your symptoms, physical exam, and results from sleep studies and other tests — into account, the doctor can determine whether your situation meets the established criteria for narcolepsy.
Narcolepsy type 1 and type 2 have distinct criteria. One important differentiating factor between the two disorders is whether or not you have cataplexy, which is a sudden and temporary loss of muscle tone that commonly occurs with positive emotions. Cataplexy only occurs in NT1.
A comparison of the diagnostic criteria is listed in the following table:
|Narcolepsy Type 1||Narcolepsy Type 2|
|The patient must meet both of the following criteria:
||The patient must meet all five of the following criteria:
It is possible for a person’s diagnosis to change over time. Around 10% of people who are initially diagnosed with NT2 will develop cataplexy at a later date, at which point their diagnosis is reclassified as NT1.
Narcolepsy can be difficult to diagnose because other conditions can mimic its symptoms.
Sleep deprivation can cause excessive daytime sleepiness, and as many as one-third of Americans fail to sleep enough. Sleep disorders like insomnia and sleep apnea, as well as multiple neurological and mental health conditions, can also cause EDS.
Although cataplexy is highly specific to NT1, it may be mistakenly identified as a seizure or stroke. Other symptoms like sleep paralysis and hallucinations can occur independently of narcolepsy and as symptoms of other disorders as well.
Unlike NT1, which can be identified with a test for CSF hypocretin levels, there is no definitive test or biomarker for NT2. Because its symptoms overlap with those of other disorders like idiopathic hypersomnia and insufficient sleep syndrome, doctors frequently have to use careful judgment to make a differential diagnosis.
The same diagnostic process and criteria for narcolepsy are used for children, teens, and adults. That said, there may be special considerations when evaluating younger patients:
If you’re planning to talk with your doctor about narcolepsy, being ready for your appointment helps. Be prepared to carefully describe your symptoms and how long you’ve had them. You may also benefit from bringing a list of questions. Examples of potential questions include: