Narcolepsy can usually be diagnosed by observing how you sleep and ruling out other conditions.
If you think you may have narcolepsy, you should see your GP. Before your appointment, it may be useful to record your symptoms in a diary or complete an Epworth sleepiness questionnaire.
Your GP will take a close look at your medical and family history. They will ask about your sleeping habits and any other symptoms you are experiencing.
Ruling out other conditions
Narcolepsy can sometimes be difficult to diagnose because the symptoms may be attributed to other conditions, such as sleep apnoea, epilepsy, depression, an underactive thyroid gland (hypothyroidism), or a previous head injury.
Excessive daytime sleepiness can also sometimes be caused by the side effects of certain medications.
Your GP may therefore carry out several tests to try to rule out any other conditions that may be causing your symptoms. For example, you may have a physical examination, blood pressure tests, and blood tests.
If your GP thinks you may have narcolepsy, they will refer you to a specialist in sleep disorders, who will analyse your sleep patterns. There are many different ways your sleep can be analysed.
Epworth sleepiness scale
The Epworth sleepiness scale (PDF, 64kb) is a questionnaire used to assess how likely you are to fall asleep while undertaking different activities. Your GP will use the results of your completed questionnaire to decide whether to refer you to a sleep specialist.
When you fill out the questionnaire, you will be asked to rank the likelihood that you will fall asleep in situations such as sitting and reading, watching television, and travelling as a passenger in a car.
A score of 10 or below indicates you have a level of daytime sleepiness equal to the general population. A score of 11 or above indicates you have an increased level of daytime sleepiness. If this is the case, your GP will probably refer you to a sleep specialist for further investigation.
Polysomnography is an investigation of your sleep carried out at a specialist sleep centre. The study usually involves staying overnight at the sleep centre so your sleeping patterns can be analysed.
During the night, several different parts of your body will be carefully monitored using electrodes and bands that are placed on the surface of your body while you sleep. Sensors will also be placed on your legs and an oxygen sensor is attached to your finger.
A number of different tests will be carried out during polysomnography, including:
- electroencephalography (EEG) – which monitors brain waves
- electrooculography – which monitors eye movements
- electromyography (EMG) – which monitors muscle tone
- recordings of movements in your chest and abdomen
- recordings of airflow through your mouth and nose
- pulse oximetry – which measures your heart rate and blood oxygen levels
- electrocardiography (ECG) – which monitors your heart
Sound recording and video equipment may also be used to record sound and images.
After you have slept, a specialist will analyse your test results to determine whether you have normal brain wave activity, breathing patterns, and muscle and eye movement.
Multiple sleep latency test
A multiple sleep latency test measures how long it takes for you to fall asleep during the day. You may have this test after polysomnography.
You will be asked to take several naps throughout the day, and a specialist will analyse how quickly and easily you fall asleep.
If you have narcolepsy, you will usually fall asleep easily and enter rapid eye movement (REM) sleep very quickly.
You may also have a blood test to find out whether you have a genetic marker known as HLA DQB *0602, which is associated with narcolepsy. A positive result supports a diagnosis, but doesn't make it 100% certain – 30% of people without narcolepsy also have the genetic marker.
Measuring hypocretin (orexin) levels
Many cases of narcolepsy are linked to a deficiency in the sleep-regulating brain chemical hypocretin, also known as orexin.
Recent research has shown that measuring the level of hypocretin in your cerebrospinal fluid, which surrounds the brain and spinal cord, can be useful in diagnosing narcolepsy.
To measure your level of hypocretin, a sample of cerebrospinal fluid is removed using a needle during a procedure called a lumbar puncture.
This test is increasingly being used by sleep disorder specialists to help make a diagnosis.