In the past, it was common for people with symptoms of narcolepsy to go undiagnosed, sometimes for many years. With greater recognition of the condition, and greater awareness amongst the medical profession, the situation is improving, but misdiagnosis of narcolepsy, and thus inappropriate treatment, is still relatively common.
Epworth Sleepiness Scale
Patients who suspect they may have narcolepsy should visit a GP in the first instance. It is useful to take a 'sleep diary' and/or a completed Epworth Sleepiness Scale questionnaire to the GP. The Epworth scale is an internationally accepted means of measuring daytime sleepiness, the major symptom of narcolepsy. If your score is 10 or below this indicates a level of daytime sleepiness found in the general population. A score of 18 or more indicates that you have very marked daytime sleepiness and that you should seek medical attention.
If a GP suspects that you may have narcolepsy they will most likely refer you to a specialist Sleep Centre. Once there, a careful history will be taken to determine the types of symptoms you are experiencing, the age when the first symptoms were noticed etc.
You can find a list of specialist Sleep Centres here.
Often a definitive diagnosis can be made on the basis of observed symptoms such as excessive daytime sleepiness and cataplexy. Otherwise, further investigations may be made. The commonest of these are:
Polysomnographic testing: a measurement of the electrical activity of the brain, eye and muscle movement and breathing as you fall asleep and whilst asleep.
Multiple Sleep Latency Test (MSLT): essentially repeated measurement of how rapidly you fall asleep - this is called 'sleep latency'. People with narcolepsy usually fall asleep rapidly and thus have low sleep latency. The type of sleep they enter into from consciousness will be recorded. Evidence that they pass directly into REM sleep is regarded as being positive for narcolepsy.
Further tests may involve taking a blood sample for analysis of tissue type, or even a sample of cerebrospinal fluid (CSF) for measurement of hypocretin (orexin) concentration. In subjects with narcolepsy, CSF hyprocretin values are generally greatly reduced – see What causes narcolepsy? Low hypocretin values are therefore a strong indicator of narcolepsy.