Which studies are included in the evaluation of narcolepsy?

Updated: Sep 04, 2019
  • Author: Sagarika Nallu, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Sleep studies are an essential part of the evaluation of patients with possible narcolepsy. The combination of an overnight polysomnogram (PSG) followed by a multiple sleep latency test (MSLT) can provide strongly suggestive evidence of narcolepsy while excluding other sleep disorders.

Human leukocyte antigen (HLA) typing may provide collateral data, but it is more useful for excluding the diagnosis by documenting that the patient does not have either DQB1*0602 or DQA1*0602. HLA typing is less valuable for confirming the diagnosis, in that HLA-DR2 and DQw1 are present in 20-30% of the general population.

Measurement of hypocretin (orexin) levels in the cerebrospinal fluid (CSF) may help establish the diagnosis. [18] CSF hypocretin levels lower than 110 pg/mL are included in the diagnostic criteria for narcolepsy in the second edition of the International Classification of Sleep Disorders (ICSD-2). On the other hand, high CSF hypocretin levels do not exclude the diagnosis of narcolepsy.

In most cases, imaging studies are unrevealing. A few small studies have implicated magnetic resonance imaging (MRI) changes of the pons within the reticular activating system. Imaging studies such as MRI are useful for excluding rare causes of symptomatic narcolepsy. Structural abnormalities of the brain stem and diencephalon may present as idiopathic narcolepsy. In patients with secondary narcolepsy, MRI of the brain may show various abnormalities that correspond to the underlying cause.


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