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Patients will typically seek medical care when they find that overwhelming drowsiness is causing them to fall asleep at inappropriate times or preventing them from functioning effectively. In many cases, patients with narcolepsy go undiagnosed for many years, believing that their daytime drowsiness is normal, and do not seek medical assistance until symptoms such as cataplexy (a sudden, uncontrollable loss of muscle tone) occur.

Before diagnosing narcolepsy, a physician will perform a complete physical examination and compile a thorough medical history. Diagnosing narcolepsy can be difficult because symptoms related to the disorder mimic those of other conditions that may disrupt patterns of consciousness. These include depression, seizure disorders, fainting and simple tiredness resulting from inadequate sleep. In addition, other sleep disorders – such as sleep apnea (temporary cessation of breathing during sleep), insomnia (inability to sleep) or restless leg syndrome (sleep disorder characterized by leg discomfort during sleep) – can cause drowsiness similar to that experienced during narcolepsy.

If the physician determines that narcolepsy is a likely diagnosis, the patient may be referred to a sleep specialist. Patients may be asked to complete the Epworth Sleepiness Scale, in which they will be asked about a number of day-to-day situations and whether or not those circumstances typically make them sleepy. Another diagnostic tool called the Stanford Narcolepsy Questionnaire can provide important information about a patient’s narcolepsy in general and cataplexy in particular.

In many cases, patients will be asked to stay overnight at a sleep center and participate in a sleep study that allows experts to closely monitor their sleep habits. Prior to the visit, patients may be asked to keep a diary that tracks their sleep patterns for a week or two.

On the night of the visit to the sleep center, electrodes are placed on the patient’s scalp and other body parts as part of a procedure known as a polysomnogram. During this test, the electrical activity or movement of the heart, brain, muscles and eyes are measured. A polysomnogram helps indicate how much time elapses before a patient falls asleep. Shorter periods may indicate narcolepsy.

Patients may also undergo a multiple sleep latency test, which measures the length of time it takes a patient to fall asleep during the day. As part of this test, the patient is asked to take four or five naps spaced two hours apart. Experts observe how long it takes the patient to enter into rapid eye movement (REM) sleep. Patients with narcolepsy typically fall asleep much faster (less than five minutes) than those who do not have the disorder (who tend to fall asleep after 10 to 20 minutes).

Narcolepsy is formally diagnosed when a patient is unable to resist falling asleep on a daily basis for a period of at least three months. The patient must feel refreshed upon awakening and experience either cataplexy, recurrent episodes of REM sleep during the transition between sleep and wakefulness (as evidenced by the presence of <1>hypnagogic hallucinations or sleep paralysis), or both. Although a polysomnogram is not necessary to diagnose narcolepsy, most physicians will recommend one to identify specific symptoms of a patient’s condition and potentially help with treatment.