Narcolepsy is a chronic (long-term) neurological sleep disorder affecting at least 135,000 to 200,000 Americans. The primary symptom of narcolepsy is excessive daytime sleepiness. Narcolepsy symptoms occur because of problems with the brain’s ability to regulate sleep-wake cycles.

A typical sleep cycle consists of two phases, rapid eye movement (REM) sleep and non-REM (NREM) sleep. During REM sleep, dreams occur, and muscle tone is temporarily lost to prevent physical responses to dreams. Normally, REM sleep begins within an hour to 90 minutes of falling asleep. However, people with narcolepsy often enter REM in just 15 minutes.

Because of the way the brain misregulates sleep in people with narcolepsy, REM sleep, NREM sleep, and wakefulness do not exist as independent states. As a result, people with narcolepsy can experience symptoms associated with REM sleep when they’re awake.

How Is Narcolepsy Diagnosed?

Narcolepsy is diagnosed through a combination of medical history evaluation and specific tests. Unfortunately, the process can be challenging and time-consuming. Many people wait years and see multiple doctors before being diagnosed. Advances in research and expanding awareness of narcolepsy are contributing to shorter diagnostic delays.

There are several reasons a diagnosis of narcolepsy may be delayed. One factor is age of onset. A survey of 1,699 people with narcolepsy in the United States found that onset of symptoms before age 18 was a predictor of delayed diagnosis.

Another factor in diagnostic delay is the existence of related conditions, such as sleep disorders, that might confuse or complicate the process. In the study mentioned above, researchers found that people with narcolepsy who also have obstructive sleep apnea experienced a delay of six to seven years before receiving a narcolepsy diagnosis. Sometimes people with narcolepsy are misdiagnosed with vitamin deficiencies, depression, insomnia, blood pressure problems, and other health conditions.

Delayed diagnosis can have a negative impact on quality of life. In a study of 52 people with type 1 narcolepsy, participants reported less anxiety and reduced criticism from friends, family, and professional associates following their diagnosis.

Diagnostic Criteria for Narcolepsy

In 2014, the International Classification of Sleep Disorders (ICSD-3) introduced updated diagnostic criteria for narcolepsy, redefining its subtypes. What used to be known as narcolepsy with cataplexy was reclassified as type 1 narcolepsy. What was known as narcolepsy without cataplexy was reclassified as type 2 narcolepsy. Cataplexy is a sudden loss of muscle tone, usually triggered by strong emotions, such as anger or excitement. It remains a key feature in type 1 narcolepsy.

Another distinction between type 1 and type 2 narcolepsy is the level of hypocretin, also known as orexin, in the cerebrospinal fluid (CBF). Hypocretin is a brain chemical that helps regulate sleep, among other functions. Low levels of hypocretin are present in approximately 90 percent of people with type 1. Among those with type 2, 25 percent to 33 percent have low hypocretin levels. Cataplexy and hypocretin levels are both important factors in diagnostic criteria for narcolepsy.

Type 1 Narcolepsy Diagnostic Criteria

For an official diagnosis of type 1 narcolepsy, a person must experience at least three months of excessive daytime sleepiness that cannot be explained by another health condition or medication use. Additionally, they must experience one of the following:

• Cataplexy and a positive multiple sleep latency test (MSLT) result
• Low hypocretin levels, measured as less than one-third of normal levels in the cerebrospinal fluid

Type 2 Narcolepsy Diagnostic Criteria

A person must meet the following criteria to be officially diagnosed with type 2 narcolepsy:

• At least three months of excessive daytime sleepiness that cannot be explained by another health condition or medication use
• A positive MSLT result

Type 1 narcolepsy is typically easier to diagnose because cataplexy and low hypocretin levels provide clear diagnostic markers. Diagnosing type 2 narcolepsy can be more challenging since it lacks these specific markers.

Secondary Narcolepsy Diagnosis

Secondary narcolepsy is a rare type of narcolepsy caused by an injury to the hypothalamus, the region at the base of the brain that regulates sleep. People with secondary narcolepsy often exhibit signs of neurological damage and tend to sleep for 10 or more hours daily. Diagnosis typically involves identifying these symptoms, a positive MSLT result, and sometimes an MRI to confirm hypothalamic damage.

Testing for Narcolepsy

Doctors use several evaluations and tests to diagnose narcolepsy. The process typically begins with a discussion about symptoms with a health care provider. Based on this conversation, the doctor will consider various potential causes and decide which tests are necessary to confirm narcolepsy or another condition.

Talk to your doctor about how to prepare for any sleep tests they recommend. You may need to stop taking medications that could affect your sleep or maintain a sleep log in the weeks leading up to the test.

Medical History

A thorough medical history is often the first step to diagnosing narcolepsy. A neurologist or sleep specialist will ask about symptoms of narcolepsy, including:

• Excessive daytime sleepiness
• Cataplexy
• Hallucinations
• Sleep paralysis

You may be asked to complete the Epworth Sleepiness Scale questionnaire, which measures your likelihood of falling asleep in various situations. Children may be evaluated using a special pediatric questionnaire. Your score can help your health care provider determine the next steps for diagnosing the cause of your symptoms. Information gathered in your medical history can also help your provider determine if conditions other than narcolepsy could be responsible for your symptoms.

Differential Diagnosis

Differential diagnosis — the process of ruling out other potential causes of symptoms — is a key step in diagnosing narcolepsy. Many other sleep disorders, medical conditions, mental health issues, and medications can contribute to similar symptoms.

During your diagnostic evaluation, your health care provider may consider the following alternative causes:

• Sleep disorders, such as obstructive sleep apnea and idiopathic hypersomnia
• Neurological disorders that affect brain function
• Mental health conditions, like depression or bipolar disorder
• Medication or substance use, including opioids and benzodiazepines like diazepam (Valium) or alprazolam (Xanax)

Differential diagnosis is especially important in identifying type 2 narcolepsy because it lacks clear defining characteristics like cataplexy or low hypocretin levels.

Polysomnogram

A polysomnogram (PSG) is an overnight sleep study used to diagnose narcolepsy and other sleep disorders, such as sleep apnea. Conducted in a sleep center, a PSG monitors a person’s nighttime sleep patterns. While a person sleeps, the polysomnogram records their eye movements, brain waves, breathing, and muscle activity. This data helps doctors determine whether a person has narcolepsy or another sleep condition.

Multiple Sleep Latency Test

An MSLT assesses excessive daytime sleepiness and usually follows a PSG. During the MSLT, a person takes five short naps, spaced two hours apart throughout the day. The test measures how quickly a person falls asleep (sleep latency) and how soon they enter REM sleep.

A positive MSLT result is a key diagnostic criterion for both type 1 and type 2 narcolepsy. The test is considered positive if the person’s average sleep latency is eight minutes or less and if REM sleep occurs in at least two of the five naps.

The MSLT is not a perfect test, and false negatives or inconsistent results can occur. A study of 36 people with type 2 narcolepsy found that 53 percent had a change in diagnosis after a second MSLT. Variable MSLT results can be due to environmental factors, age, or different testing procedures among different sleep labs. This inconsistency is a greater challenge in diagnosing type 2 narcolepsy, which lacks definitive markers like cataplexy or low hypocretin levels.

Actigraphy

Actigraphy is a noninvasive method of measuring sleep and wake cycles over several days or weeks. The actigraph, worn on the wrist like a sports watch, tracks movement to monitor sleep patterns. This test can help determine if sleep symptoms are due to a circadian rhythm disorder. Some sleep specialists may recommend actigraphy monitoring for a few weeks before proceeding with PSG or MSLT testing.

Hypocretin Level Test

Low levels of hypocretin are a defining feature of type 1 narcolepsy. Your doctor may test your cerebrospinal fluid to evaluate your hypocretin levels. This involves a lumbar puncture (sometimes referred to as a spinal tap) to collect the CBF. While low hypocretin levels are one of the diagnostic criteria for type 1 narcolepsy, CBF testing is not common. It is typically reserved for cases where MSLT results are inconclusive or cataplexy presents in an unusual pattern.

Genetic Testing

Many people with narcolepsy carry a specific genetic marker called HLA-DQB1*06:02. However, this gene is also found in people without narcolepsy. While genetic testing cannot confirm narcolepsy, it can be helpful when diagnosis is challenging due to inconclusive test results or atypical symptoms.

Talk to Your Doctor

Diagnosing narcolepsy can be a complex process that involves various tests. Given the challenges and potential delays in diagnosis, it’s essential to engage openly with your doctor or health care team. Don’t hesitate to ask questions about your symptoms, the testing process, or the steps involved in narrowing down a diagnosis. Be sure to communicate any new or changing symptoms, as this can provide valuable insight. Working closely with your doctor will ensure that you get the most accurate diagnosis and the best possible care for treating your condition.

Find Your Team

On MyNarcolepsyTeam, the social network for people with narcolepsy and their loved ones, more than 11,000 members come together to ask questions, give advice, and share their stories with others who understand life with narcolepsy.

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