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Narcolepsy

Description

An in-depth report on the causes, diagnosis, and treatment of narcolepsy.

Diagnosis

Although narcolepsy is a physical disorder, doctors are still very likely to misdiagnose patients as having psychologic problems. It often takes a year or longer for a patient with narcolepsy to receive a correct diagnosis. To determine specific sleep disorders, the doctor will take a medical and family history and should be told of any medications being taken. The symptoms of narcolepsy are sometimes undeniable if the patient reports all of the major symptoms:

• Excessive daytime sleepiness with a tendency for frequent naps. (These frequent naps should occur every day for at least 6 months to serve as a diagnosis of narcolepsy.) Narcolepsy is usually diagnosed in adolescence and young adulthood when falling asleep suddenly in school brings the problem to attention.
• Cataplexy (abrupt loss of muscle tone or weakness that causes a person to stop all motor activity).
• Hypnagogic hallucinations (vivid visual or auditory phenomena) experienced at the onset of sleep.
• Sleep paralysis (an inability to move on first awakening).

Diagnosis based only on symptoms, however, is often problematic for various reasons:

• Patients often seek medical help for single symptoms (sleep paralysis or hypnagogic hallucinations) that might be associated with other disorders, particularly epilepsy.
• Symptoms are sometimes not dramatically apparent for years, even to the patient or a skilled observer. In one study, the average number of years between onset of symptoms and diagnosis was 14. Another study conducted in a sleep clinic reported that more than half of patients were diagnosed when they were over 40 and had not realized they had narcolepsy until they experienced a bout of cataplexy.

In some cases, the patient may need to consult a sleep specialist or go to an accredited sleep disorders center for accurate diagnosis of a sleep disorder. Patients should carefully investigate centers to make sure that they offer full sleep studies. Patients who visit a sleep center undergo an in-depth analysis, usually supervised by a multidisciplinary team of consultants who can provide both physical and psychiatric evaluations.

Questionnaires

A doctor may administer certain questionnaires on sleeping habits.

The Epworth Sleepiness Scale. The Epworth sleepiness scale (ESS) uses a simple questionnaire to measure excessive sleepiness. It is proving to be a very accurate measure for assessing narcolepsy.

THE EPWORTH SLEEPINESS SCALE
SITUATION	CHANCE OF DOZING 0 = no chance of dozing 1 = slight chance of dozing 2 = moderate chance of dozing 3 = high chance of dozing
Sitting and reading	(Indicate a score of 0 to 3)
Watching TV	(Indicate a score of 0 to 3)
Sitting inactive in a public place (a theater or a meeting)	(Indicate a score of 0 to 3)
As a passenger in a car for an hour without a break	(Indicate a score of 0 to 3)
Lying down to rest in the afternoon when circumstances permit	(Indicate a score of 0 to 3)
Sitting and talking to someone	(Indicate a score of 0 to 3)
Sitting quietly after a lunch without alcohol	(Indicate a score of 0 to 3)
In a car, while stopped for a few minutes in traffic	(Indicate a score of 0 to 3)
SCORE RESULTS	1-6: Getting enough sleep 4-8: Tends to be sleepy but is average 9-15: Very sleepy and should seek medical advice Over 16: Dangerously sleepy

Multiple Sleep Latency Test. The multiple sleep latency test (MSLT) uses a machine that measures the time it takes to fall asleep lying in a quiet room during the day. The patient takes 4 or 5 scheduled naps 2 hours apart. People with healthy sleep habits fall asleep in about 10 to 20 minutes. In patients with narcolepsy, polysomnography plus MSLT will show a much shorter duration of time (less than 8 minutes) from wakefulness into sleep. At least 2 of the naps are REM-onset (the active sleep phase associated dreaming). The test has limitations, however, and is most useful for measuring the severity of the problem. The Epworth sleepiness scale may be more accurate in differentiating narcolepsy from normal daytime sleepiness.

Polysomnography

An overnight polysomnography (sleep study) can be a valuable means for determining the basic cause of sleepiness. The patient arrives at the sleep center about two hours before bedtime without having made any changes in daily habits. The patient is hooked up to a battery of monitoring devices:

• Electroencephalogram, or EEG (monitors the electrical activity of the brain)
• Electrocardiogram or ECG (monitors the heart)
• Electromyogram (monitors the movements of muscles)
• Electrooculogram (monitors eye movements)

These instruments record activity as the patient passes, or fails to pass, through the various sleep stages. One study using polysomnography reported that both healthy patients and those with narcolepsy perform equally during the first 5 to 10 minutes of the test, but after that, patients with narcolepsy show evidence of drowsiness and even indications of sleep. In general, however, polysomnography is most useful for ruling out other disorders, such as sleep apnea, in people with narcolepsy.

Testing Spinal Fluid for Hypocretin

Testing the patient's spinal fluid to detect deficiencies in hypocretin may be a useful method for diagnosing narcolepsy. Low levels may indicate narcolepsy. (Low levels, however, can also occur with brain injury or Guillain-Barre syndrome.) Some researchers believe that measuring hypocretin levels may identify people with early or mild symptoms of narcolepsy (such as cataplexy without altered consciousness). This would help avoid inaccurate diagnoses such as epilepsy or psychosis, which require potent drugs that have significant side effects and are not helpful for patients with narcolepsy.

Investigative Diagnostic Procedures

Transcranial Magnetic Stimulation. An investigative test uses an instrument that magnetically stimulates part of the brain to produce cataplexy. In one study of patients with narcolepsy, such stimulation caused loss of muscle tone in certain areas when patients were off their medication, but had no effect when they were in treatment.

Ruling out Other Disorders

Ruling out Psychologic Disorders. In one study, 40% of patients who actually had narcolepsy had been diagnosed incorrectly with some psychological or psychiatric problem. Certainly, patients with narcolepsy have emotional difficulties because of the condition and it is often difficult, particularly for a nonspecialist, to detect the physical problem. Even worse, hypnagogic hallucinations may result in diagnoses of schizophrenia or bipolar disorder, which are treated with potent antipsychotic drugs that have severe side effects and are useless for narcolepsy.

Ruling out Epilepsy. Narcolepsy can easily be mistaken for epilepsy, a group of disorders that cause seizures. Case studies have reported a misdiagnosis of epilepsy in patients who were actually experiencing cataplexy and sleep paralysis.

Other Causes of Persistent Fatigue. A number of conditions can cause persistent fatigue and should be ruled out:

• Obstructive sleep apnea. This is a major sleep disorder that causes fatigue and afternoon sleepiness and must be ruled out before a diagnosis of narcolepsy can be established. (A person may also suffer sleep apnea and narcolepsy at the same time.)
• Chronic fatigue syndrome
• Head trauma
• Infectious mononucleosis

• Guillain-Barre syndrome
• Hepatitis
• Atypical pneumonia, particularly those involving echoviruses

Other Causes of Sleep Paralysis. Sleep paralysis may be triggered by certain conditions, such as:

• Irregular sleep habits
• Sleep deprivation
• Shift work
• Jet lag
• Psychologic stress

These conditions may also worsen sleep paralysis in narcolepsy. Narcolepsy sleep paralysis usually occurs at the onset of sleep and is chronic.

• Review Date: 7/13/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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