Narcolepsy Workup

Updated: May 09, 2017
  • Author: Sagarika Nallu, MD; Chief Editor: Selim R Benbadis, MD  more...
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Workup

Approach Considerations

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. [16] 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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Sleep Studies

An overnight PSG followed by an MSLT can exclude other causes of excessive daytime sleepiness (EDS), especially sleep apnea, and can provide information about EDS by measuring sleep latency and sleep-onset rapid eye movement periods (SOREMPs). The overnight PSG findings typically are normal in narcolepsy, though they may show sleep fragmentation. All central nervous system (CNS) stimulants and sedative-hypnotics should be discontinued 2 weeks before the PSG and MSLT.

The MSLT involves 5 opportunities to nap at 2-hour intervals over the day. More than 2 SOREMPs and a mean sleep latency of less than 8 minutes strongly suggest narcolepsy. These findings are not completely specific and also can be seen in patients with severe sleep deprivation, delayed sleep phase disorder, or severe sleep apnea. For these reasons, a PSG of the previous night is necessary for interpretation of the MSLT; MSLT cannot be used alone to confirm or rule out narcolepsy.

Diagnosing narcolepsy in children presents numerous difficulties. One study found that 85% of children with narcolepsy also suffered from sleep-disordered breathing. Serial MSLTs may be required, and usually multiple confounding factors are involved (eg, increased alertness in the novel environment of the sleep laboratory). Furthermore, normative MSLT values for children have not been established.

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