Identifying hypersomnia
Idiopathic hypersomnia should be considered when a patient’s excessive sleep or EDS are not better explained by another sleep disorder, other medical or psychiatric disorders, or the use of illicit drugs or medications.4 Idiopathic hypersomnia is characterized by EDS that occurs in the absence of cataplexy and is accompanied by no more than 1 sleep-onset REM (SOREM) period on an MSLT and the preceding PSG combined. The differential diagnosis includes narcolepsy, sleep apnea, and other conditions; most importantly, insufficient sleep syndrome must be carefully considered and excluded.
In IH, evidence of hypersomnia must be demonstrated by an MSLT showing a mean sleep latency of <8 minutes or by PSG or wrist actigraphy showing a total 24-hour sleep time of >660 minutes.4 A prolonged and severe form of sleep inertia, consisting of prolonged difficulty waking up with repeated returns to sleep, irritability, automatic behavior, and confusion, often occurs in IH but is not pathognomonic.4
Naps are long—often 60 minutes—and described as unrefreshing by 46% to 78% of patients.4 Sleep efficiency on polysomnography is usually high (mean 90% to 94%). Self-reported total sleep time is longer than in controls and is >10 hours in at least 30% of patients.4 Unfortunately, symptoms and certain objective findings of IH are not unique to the disorder and are considered ubiquitous.
For Mr. W, a diagnosis of narcolepsy was unlikely due to his MSLT results. Patients with narcolepsy have cataplexy (REM dissociation) and/or at least 2 SOREM periods on MLST, or at least 1 SOREM period on MLST in conjunction with a SOREM on the preceding PSG,4 which Mr. W did not exhibit. Patients with narcolepsy typically take refreshing naps lasting 15 to 30 minutes. Although not unique to narcolepsy, common findings include hypnagogic hallucinations and sleep paralysis. Patients with narcolepsy typically do not have sleep inertia but, when seemingly awake, have lapses in vigilance sometimes in combination with automatic behavior, such as writing gibberish or interrupting a conversation with a completely different topic. Another characteristic PSG finding is moderate to severe sleep fragmentation, which may be due to associated periodic limb movements or instability in sleep/wake transitions.5 Mr. W had no history of traumatic brain injury that would suggest hypersomnolence secondary to a brain injury.
Among medical conditions, OSA is the predominant cause of EDS, but this, too, was unlikely for Mr. W because the CPAP therapy reports indicated excellent chronic use and effect. His apnea/hypopnea index was low, and the lowest oxygen saturation recorded on his pre-MSLT PSG using CPAP was 93%. Subjectively, Mr. W reported no choking, gasping, or snoring while receiving CPAP therapy.
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