Primary Hypersomnia Workup

Updated: Sep 04, 2018
  • Author: Adrian Preda, MD, DFAPA; Chief Editor: Ana Hategan, MD, FRCPC  more...
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Approach Considerations

Hypersomnolence is a diagnosis of exclusion. Other causes of excessive daytime somnolence should be ruled out before a diagnosis of hypersomnolence is made.

Patients should receive a complete blood count (CBC), screening biochemistry tests, and thyroid-stimulating hormone tests to exclude common physical disorders that may present with complaints of excessive tiredness, often expressed as excessive sleepiness by patients. A drug screen is indicated if substance-induced sleep disorder needs to be ruled out.

As excessive sleepiness is essentially a self-reported, subjective complaint, a number of tests have been created with the goal of increasing the data collection validity and reliability. Commonly used scales for a quantitative, systematic assessment of excessive sleepiness are the Epworth Sleepiness Scale and the Stanford Sleepiness Scale. While helpful, these scales remain essentially subjective in nature, which raises questions about the characteristics of sleepiness as assessed by subjective methods (e.g., the Epworth and Stanford sleepiness scales) versus objective ones (e.g., polysomnography and the Multiple Sleep Latency Test). [80, 78]


Polysomnography and Multiple Sleep Latency Test

Complete in-laboratory polysomnography (PSG) studies are essential to exclude other sleep disorders, particularly sleep breathing disorder, periodic limb movement disorder, and narcolepsy. Nocturnal PSG findings in hypersomnolence include a short sleep latency, absence of arousals or awakenings, normal distribution of REM and NREM sleep, and normal to prolonged sleep duration. [79, 81]

A PSG study completion is required prior to the Multiple Sleep Latency Test to objectively characterize preceding sleep and uncover potential causes of sleep fragmentation. The PSG must have confirmed at least 6 hours of sleep for the Multiple Sleep Latency Test results to be considered in diagnosing hypersomnolence. Typical PSG findings in idiopathic hypersomnia include shortened sleep latency, increased sleep efficiency (often >90%), and increased slow wave sleep [82, 10, 47, 56, 13]   It should be noted that these are nonspecific findings and could be present in behaviorally induced insufficient sleep syndrome (BIISS). [13]  Some studies report increased frequency of sleep spindles either throughout the sleep period or at the beginning and end of the night in idiopathic hypersomnia. [83, 69]  It should be noted that SOREMPs are rare in idiopathic hypersomnia (IH). Indices for arousal, apnea-hypopnea, and periodic limb movements (PLM) are generally less than 5 to 10 per hour. Other studies have a belief that PLM in a patient with excessive daytime sleepiness who does not have a diagnosis of restless legs syndrome (RLS) should not preclude giving a diagnosis of IH—occasionally higher indices are seen. [10, 47, 59, 61, 13]   

Sleep latency on the Multiple Sleep Latency Test is short, with a mean sleep latency time < 8 minutes. [3, 10, 47]  SOREMPs can occur in approximately 3–4% of naps but by definition will not occur more than once. This is contrasted with narcolepsy, where sleep-onset REM periods (the occurrence of REM sleep within 20 minutes of sleep onset) are observed in two or more naps.

Breathing-related sleep disturbances and frequent limb movements disrupting sleep are not present.

The following PSG features are required for the diagnosis of hypersomnolence:

  • A sleep period that is normal or prolonged in duration

  • Normal REM sleep latency

  • A mean sleep latency score of less than 8 on the Multiple Sleep Latency Test

  • Fewer than 2 sleep-onset REM periods.

The Multiple Sleep Latency Test is performed to evaluate the presence of pathologic sleepiness. The subject is studied during 5 daytime naps taken 2 hours apart. According to 2 studies, the mean Multiple Sleep Latency Test score in hypersomnolence is slightly higher than the score in narcolepsy. The mean Multiple Sleep Latency Test score was found to be 6.5 ± 3.2 minutes for idiopathic hypersomnolence versus 3.3 ± 3.3 minutes for narcolepsy. Narcolepsy is excluded by the absence of sleep-onset REM periods on the 5-nap Multiple Sleep Latency Test.



In recurrent primary hypersomnia (ie, Kleine-Levin syndrome), routine electroencephalographic studies performed during hypersomnia show a general slowing of the background rhythm and paroxysmal bursts of theta activity. Nocturnal PSG shows prolonged sleep duration and decreased sleep latency (< 10 min). In addition, sleep-onset REM has been reported during symptomatic periods. (See the images below.) [66, 83, 3, 10, 47]

Primary hypersomnia. Polysomnographic study demons Primary hypersomnia. Polysomnographic study demonstrates apnea (absence of carbon dioxide fluctuation indicating no flow), chest wall paradox, abrupt increase in tidal volume at the end of apnea, and oxygen desaturation. All of these features are consistent with obstructive sleep apnea.
Primary hypersomnia. In contrast to obstructive sl Primary hypersomnia. In contrast to obstructive sleep apnea, mixed apnea shows absence of respiratory efforts in the first segment of the apnea.
Primary hypersomnia. Periodic limb movements show Primary hypersomnia. Periodic limb movements show intermittent leg electromyogram activity accompanied by electroencephalogram arousals.