Narcolepsy is a neurological sleep disorder affecting an estimated 135,000 to 200,000 Americans. The primary symptom of narcolepsy is excessive daytime sleepiness (EDS). Narcolepsy symptoms occur because of problems with the brain’s ability to regulate sleep-wake cycles.
A standard sleep cycle consists of two phases, rapid eye movement (REM) sleep and non-REM (NREM) sleep. During REM sleep, people dream and experience temporary loss of muscle tone 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.
Narcolepsy is diagnosed through a combination of evaluating medical history and testing. Unfortunately, receiving a narcolepsy diagnosis can be challenging and time-consuming. In some cases, people can 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, burnout syndrome, or blood pressure problems.
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.
In 2014, the International Classification of Sleep Disorders (ICSD-3) published its third edition with updated diagnostic criteria for narcolepsy. As part of this new diagnostic criteria, the ICSD-3 redefined the types of narcolepsy. What used to be known as narcolepsy with cataplexy was reclassified as type 1 narcolepsy, and 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.
Along with cataplexy, another distinguishing factor between type 1 and type 2 narcolepsy is the level of hypocretin — sometimes called orexin — in the cerebrospinal fluid. Hypocretin is a chemical in the brain that helps to regulate sleep, among other functions. Low hypocretin levels are extremely common among people with type 1 narcolepsy and less common among those with type 2. Approximately 90 percent of people with type 1 have low levels of hypocretin compared to 10 percent to 24 percent of those with type 2. Cataplexy and hypocretin levels are both important factors in diagnostic criteria for narcolepsy.
To receive an official diagnosis of type 1 narcolepsy, a person must meet the following criteria:
And one of the following:
A person must meet the following criteria to be officially diagnosed with type 2 narcolepsy:
Secondary narcolepsy is a rare type of narcolepsy caused by an injury to the hypothalamus, the region at the base of the brain that controls sleep. People with secondary narcolepsy exhibit signs of neurological damage and tend to sleep for 10 or more hours daily. Secondary narcolepsy is usually diagnosed based on these symptoms, a positive multiple sleep latency test, and sometimes an MRI to confirm damage to the hypothalamus.
There are several different types of evaluations and tests a doctor may use to diagnose narcolepsy. In most cases, the diagnostic process starts with a conversation with your health care provider about your symptoms. From there, your doctor will consider a range of explanations for your symptoms and determine which tests are appropriate to confirm a diagnosis of narcolepsy or another condition.
Talk to your doctor about how to prepare for any sleep tests they recommend. You may be required to stop taking any medications that could interfere with your sleep or keep a sleep log in advance of the test.
A thorough medical history is often the first step to diagnosing narcolepsy. A neurologist or sleep specialist will ask about symptoms of narcolepsy, including EDS, cataplexy, hallucinations, and sleep paralysis. You may be asked to fill out the Epworth Sleepiness Scale questionnaire. Children may be evaluated using a special pediatric questionnaire. Your score can help your health care provider determine next steps for diagnosing the cause of your symptoms.4 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 — the process of ruling out other potential causes of symptoms — is an important component of diagnosing narcolepsy. There are several other sleep disorders, medical and mental health conditions, and medications or substances that could contribute to symptoms.
As part of your diagnostic process, your health care provider may consider the following alternative causes of your symptoms:
Differential diagnosis is especially important in identifying type 2 narcolepsy because it lacks clear defining characteristics like cataplexy or low hypocretin levels.
A polysomnogram is an overnight sleep study that can be used to diagnose narcolepsy and other sleep disorders like sleep apnea. The PSG will be used to evaluate your nighttime sleep patterns. A PSG takes place overnight in a sleep center. While you sleep, the polysomnogram will record your eye movements, brain waves, breathing, and muscle activity. The PSG can help determine if you have narcolepsy or another sleep condition.
A multiple sleep latency test is a daytime test used to assess excessive daytime sleepiness. The test usually occurs the day after a PSG. As part of the MSLT, you will take five short naps every two hours throughout the day. The test will measure how fast you fall asleep (known as sleep latency) and the time it takes to enter REM sleep.
A positive MSLT is a diagnostic criterion for type 1 and type 2 narcolepsy. An MSLT is considered positive, or indicative of narcolepsy, if your average sleep latency is eight minutes or less and you’ve entered REM sleep in at least two of the five naps.
The multiple sleep latency test is not a perfect test, and false negatives or inconsistent results are possible. 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 the result of environmental factors, age, or different methodologies at different sleep labs. Inconsistent results are a bigger problem in diagnosing type 2 narcolepsy because cataplexy and low hypocretin levels cannot be used to confirm the diagnosis.
Actigraphy is a noninvasive way of measuring cycles of sleep and wakefulness over days or weeks. An actigraph is worn on the wrist and looks like a sports watch. Monitoring sleep with an actigraph can help determine if sleep symptoms are caused by a circadian rhythm problem. Some sleep specialists will recommend monitoring with an actigraph for a few weeks before PSG or MSLT testing.
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 cerebrospinal fluid. While low hypocretin levels are one of the diagnostic criteria for type 1 narcolepsy, cerebrospinal fluid testing is not common. It is generally reserved for individuals suspected of having narcolepsy whose MSLT results are inconclusive and who have unusual cataplexy patterns.
Many people with narcolepsy carry a specific genetic marker — the HLA-DQB1*06:02 gene. This gene is also found in people without narcolepsy. Identifying the HLA gene doesn’t confirm narcolepsy, but testing may be helpful in cases where diagnosis is difficult due to inconclusive testing or unusual symptom presentation.