Narcolepsy - Diagnosing narcolepsy

Narcolepsy can usually be diagnosed by observing how you sleep and by 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 (see below).

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.

Therefore, your GP may carry out several tests to try and 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.

Sleep analysis

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 is a questionnaire used to help analyse situations that make you feel sleepy. 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 18 or above indicates you have a high level of daytime sleepiness. If this is the case, your GP will probably refer you to a sleep specialist for further investigation.

An online version of the Epworth sleepiness scale is available on the Narcolepsy UK website.

Polysomnography

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 while you sleep using electrodes (small metallic discs) and bands on the surface of your skin and around parts of your body. Sensors will also be placed on your legs and an oxygen sensor attached to your finger.

A number of different tests will be carried out during polysomnography, including:

• electroencephalography (EEG) – which monitors brain waves
• 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.

For the test, 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.

Measuring orexin (hypocretin) levels

Many cases of narcolepsy are linked to a deficiency in the sleep-regulating brain chemical orexin (also known as hypocretin).

Recent research has shown that measuring the level of orexin in your cerebrospinal fluid (which surrounds the brain and spinal cord) can be useful in diagnosing narcolepsy, and this test is increasingly being used by sleep disorder specialists to help make a diagnosis.

To measure your level of orexin, a sample of your cerebrospinal fluid is removed using a needle during a procedure called a lumbar puncture.