Narcolepsy

Description

Diagnosis

Although narcolepsy is now clearly known to be a physical disorder, physicians are still very likely to misdiagnose these 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 physician 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 six 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 (e.g., sleep paralysis or hypnagogic hallucinations) that might be associated with other disorders, particularly epilepsy.
• Sometimes symptoms are 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 narcolepsy 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 a sleep disorders center for accurate diagnosis of a sleep disorder. About 250 centers are accredited by the American Sleep Disorders Associations. Patients should investigate centers carefully, being sure that they offer full sleep studies. One night at a sleep clinic can be very costly and is not usually covered by insurance. At most, sleep disorders centers' patients undergo an in-depth analysis, usually supervised by a multi-disciplinary team of consultants who can provide both physical and psychiatric evaluations.

Questionnaires

A physician 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.

Multiple Sleep Latency Test. The multiple sleep latency test (MSLT) employs a machine that measures the time it takes to fall asleep lying in a quiet room during the day. The patient takes four or five scheduled naps two 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 eight minutes) from wakefulness into sleep. At least two 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

In some cases overnight polysomnography is 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 in these organs as the patient passes, or fails to pass, through the various sleep stages. One study using polysomnography reported that normal and narcoleptic patients perform equally during the first five to 10 minutes of the test, but after that, patients with narcolepsy showed 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 is proving to be a useful method for diagnosing narcolepsy. Low levels have occurred in small studies in around 85% of patients. (Low levels, however, can also occur with brain injury and Guillain-Barre syndrome.) Nevertheless, 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 of problems, 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. In one study, 16% were diagnosed with depression and 17% with neurotic disorders. 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.

Swollen lymph nodes, sore throat, fatigue and headache are some of the symptoms of mononucleosis, which is caused by the Epstein-Barr virus. It is generally self-limiting and most patients can recover in 4 to 6 weeks without medications.

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

(Note, both head trauma and syndrome Guillain-Barre syndrome can also produce test results showing low levels of hypocretin in spinal fluid, just as narcolepsy can.)

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

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

These conditions may also exacerbate sleep paralysis in narcolepsy, although in the sleep disorder, narcolepsy sleep paralysis usually occurs at the onset of sleep and is chronic.