What is the role of sleep studies in the diagnosis of narcolepsy?

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

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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