What causes narcolepsy?

-The cause in the vast majority of cases has been found to be a specific problem with the chemical "neurotransmitters" that regulate communications between different groups of nerve cells in the brain. Brain cells in the lateral hypothalamus that produce a neurotransmitter called hypocretin or orexin are lost.

Why does this loss of nerve cells (neurons) occur? An explanation is being sought. We have know for some years that narcolepsy is strongly associated with specific HLA types (see below), a phenomenon that has been noted in many autoimmune disorders (conditions in which the body mounts an immune defense against its own tissues. However, it has not been shown with any certainty that narcolepsy is an autoimmune disorder and that autoimmune mechanisms are responsible for the loss of hypocretin (orexin)-containing nerve cell bodies.

-Only rare cases have been reported of narcolepsy arising as the consequence of such structural causes as brain tumors, brain infections and head injuries. CT/MRI scans of the brain are normal in the vast majority of cases.

-Narcolepsy can "run in families" such that some individuals appear genetically predisposed to develop it. However, it is not a genetic disorder per se in humans. Some breeds of dogs do develop narcolepsy on a genetic basis.

-The onset of narcolepsy sometimes follows stressful events, but such does not indicate that it is a psychological disorder.

Is narcolepsy a rare condition?

-Not at all! It is roughly as common as MS (multiple sclerosis) in the United States.

How is narcolepsy diagnosed?

-A careful history, followed by specific sleep center studies (both an overnight sleep monitoring and a multiple sleep latency test).

-An introvertible history of cataplexy is far more diagnostic of narcolepsy than a multiple sleep latency test, since both false negative and false positive MSLTs occur frequently.

Can narcolepsy be diagnosed by a "blood test"?

-No! Such is a common misimpression that resulted from the discovery that most (but not quite all) narcoleptics share particular HLA types (genetically determined markers on white blood cells that are used to determine tissue compatibility--for example, to assess one's ability to donate a kidney to a possible recipient without high likelihood that the transplanted kidney will be rejected). HLA types are evaluated with a blood test.

-There are two reasons why these tests cannot be used to diagnose narcolepsy:

--First, some definite narcoleptics who even have cataplexy will come out negative on these tests.

--Second, an even greater problem is that up to 25% of the general population will show the same HLA typing that has been associated with narcolepsy

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