Diagnosis:

Although narcolepsy is a physical disorder, doctors are still very likely to misdiagnose patients as having psychological problems. For most patients, narcolepsy is not diagnosed for up to 10 - 15 years after their symptoms first began. 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 some cases, the patient may need to consult a sleep specialist or go to an accredited sleep disorder 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.

Levels of hypocretin-1 levels in the cerebrospinal fluid (CSF) may prove valuable in diagnosing difficult cases of narcolepsy in the future, since hypocretin is often absent in patients with the condition.

Questionnaires

A doctor may administer certain questionnaires on sleeping habits, such as the Stanford Sleepiness Scale or the Epworth Sleepiness Scale.

The Epworth Sleepiness Scale. The Epworth Sleepiness Scale (ESS) uses a simple questionnaire to measure excessive sleepiness and differentiate it from normal daytime sleepiness.

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 - 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. There is no clear definition of exactly which abnormal results would indicate narcolepsy. It 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 sleep study, called polysomnography, can be a valuable means for determining the basic cause of sleepiness. The patient arrives at the sleep center about 2 hours before bedtime without having made any changes in daily habits. The patient will be monitored by a variety of devices while sleeping:

• 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.

Ruling out Other Disorders

Ruling out Other Sleep Disorders. Other sleep disorders can share some or all of the symptoms of narcolepsy:

• Patients with obstructive sleep apnea also experience sleep disturbance and excessive daytime fatigue.
• Idiopathic hypersomnia is a less well-defined syndrome in which patients have excessive daytime sleepiness without evidence of cataplexy. Patients have a hard time becoming fully awake despite an adequate amount of sleep time.
• Chronic sleep deprivation
• Secondary narcolepsy, resulting from head trauma, tumors, vascular malformations in the brain, multiple sclerosis, or Parkinson's disease

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, including:

• 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

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

Neuroimaging techniques may be used in a research setting to confirm sleep physiological theories in humans and to discover new information about the neurobiological aspects of sleep, dreams, and memory. Few neuroimaging studies have focused on patients with sleep disorders such as narcolepsy.