By Risa Kerslake, RN, BSN
Idiopathic hypersomnia (IH) is underrecognized and poorly understood. While patients typically have high sleep efficiency, it’s nonrestorative sleep, and the symptoms can take a toll on quality of life.
Sleep physicians can be challenged by the heterogeneity of the disorder’s clinical manifestations, says neurologist-sleep physician Lynn Marie Trotti, MD, MSc. There’s the “classic form” where people have daytime sleepiness but also long sleep duration and nonrestorative naps with severe sleep inertia.
“Sometimes people with IH just have unexplained sleepiness and a pattern of findings on the multiple sleep latency test [MSLT],” says Trotti, an associate professor of neurology at Emory University School of Medicine. “Right now, both of those groups are called IH. Should they continue to be considered the same disease? Are they really different diseases? We don’t know.”
Using the MSLT for Suspected IH
The MSLT is the most commonly used test for IH, but it works better to catch problems with staying awake (as in narcolepsy). However, people with IH have problems waking up.
“There’s not a clear-cut set of things that these individuals have, which makes it hard to find a screening assessment [to verify] this is the condition you’re dealing with,” says Logan Schneider, MD, an adjunct clinical associate professor of sleep medicine at Stanford Sleep Center.
While people with IH and narcolepsy both typically fall asleep in eight minutes or less on the MSLT, there’s no REM dysregulation in the naps of people with IH, notes Jose Colon, MD, who is board-certified in sleep medicine, child neurology, and lifestyle medicine. “You could objectively find the direct degree of sleepiness, so that it can be measured into a mild, moderate, or severe classification.”
Also, the MLST has poor test-retest reliability due to changes in sleep-onset REMs and sleepiness levels in IH.1 “You see people changing between IH and narcolepsy type 2, and vice versa. But you also see people changing to and from normal results, even though they’re still symptomatic,” explains Trotti.
Mood Disorders-IH Overlap
Getting a clear clinical history sometimes doesn’t help differentiate the MSLT either. Fatigue, brain fog, and sleep inertia can also manifest in depression and anxiety, says Margaret Blattner, MD, PhD, a neurologist-sleep specialist at Beth Israel Deaconess. “These absolutely go hand-in-hand. I don’t think we understand totally yet, but there is significant overlap with mood disorders and idiopathic hypersomnia.”
In these cases, it is important to treat both disorders in collaboration with a mental health provider, according to Trotti. “It’s often the case that if people’s mood disorder gets treated, they still have symptoms of hypersomnia and the converse can be true as well. Someday, scientifically, we’ll be able to distinguish those things,” she predicts.
The Sleep Inertia Questionnaire (SIQ) was originally designed to capture sleep inertia in those with mood disorders. “I thought that we might see a different pattern of answers on the SIQ in people who did and do not have depression, but we really didn’t substantially see that,” explains Trotti of the 2024 study she coauthored to assess the validity of using the SIQ in hypersomnolence disorders. (The study found the questionnaire does well in distinguishing hypersomnolent patients from healthy controls, after controlling for depression, eveningness, and medication. And that sleep inertia duration is best at distinguishing IH from narcolepsy type 1.)2
While sleep inertia is an important symptom of IH, it’s not unique to it, says Trotti. Other disorders, such as delayed sleep-wake phase disorder, can also cause pronounced sleep inertia.
Additional Ways to Quantify IH
In combination with her MSLT protocol, Trotti also uses the Psychomotor Vigilance Test to quantify sleep inertia severity. She finds it to be a complementary approach to get a better grasp on a patient’s symptoms.3 “We can see if people’s attention changes from before a nap to right after a nap,” she says.
Trotti also implements the Idiopathic Hypersomnia Severity Scale, developed by Yves Dauvilliers, MD, PhD, and his team, to capture and understand core features of IH, including sleep inertia.4 “If you don’t measure something, it’s hard to fix it,” says Trotti. “I suspect sleep inertia is going to be a symptom, like sleepiness, where there’s not going to be one perfect tool that captures all of it. We may do better with some combination of objective and self-reported data.”
The most reliable objective data appropriate for those with IH are out of reach for many sleep centers: extended polysomnography is something that’s done more in the research realm, but studies suggest that it may be a better measure of diagnosing IH than the MSLT5—and the same is true for wrist actigraphy. “Most sleep physicians would say that both of these are clinically useful tools, but the logistics of having them available for evaluation of people with severe sleepiness is very limiting,” says Blattner.
IH Therapy Options: Prescription, OTC, and Behavioral
Sometimes, a drug trial can be helpful when there’s a suspicion of IH. “If you have a response to therapy, it might suggest patients are potentially having at least a sleep dysfunction that is resolvable with that medication that’s not otherwise explainable,” says Schneider.
Schneider was involved in a 2025 post-hoc analysis of a phase 3 trial assessing low-sodium oxybate for idiopathic hypersomnia. His team identified 10 to 12 mm as a minimal clinically important difference for the self-reported Visual Analog Scale for Sleep Inertia on a scale of 0 to 100.6
“Which makes sense—about 10% change of improvement might be about how much you might imagine somebody can quantify as a perceivable level of improvement,” says Schneider.
Caffeine, no more than 200 mg, at least three hours apart, and not after 2 pm, can be helpful for this population too. But patients must understand how much caffeine they’re consuming by paying attention to how many milligrams are in their drinks, Colon advises. “I counsel caffeine use because patients are doing it already, and we want them to do it right,” he says.
Interventions such as setting warning alarms that it’s time to wake up soon, alarms that prod people to get out of bed to shut them off, and enlisting the help of family members to help physically get patients out of bed can sometimes be helpful.
Colon advises his patients, “When the alarm goes off, your feet hit the ground. Don’t turn the alarm off without your feet hitting the ground first.” He also promotes low-glycemic diets, since high-carbohydrate states can make people sleepy.7
The sleep medicine subspecialty may not yet fully understand IH yet. But for patients, even small steps toward clarity can mean major leaps in quality of life.
References
1. Trotti LM, Staab BA, Rye DB. Test-retest reliability of the multiple sleep latency test in narcolepsy without cataplexy and idiopathic hypersomnia. J Clin Sleep Med. 2013 Aug 15;9(8):789-95.
2. Sung ER, Maness CB, Cook JD, et al. Validation and performance of the sleep inertia questionnaire in central disorders of hypersomnolence. Sleep Med. 2024 Sep;121:352-8.
3. Trotti LM, Saini P, Bremer E, et al. The Psychomotor Vigilance Test as a measure of alertness and sleep inertia in people with central disorders of hypersomnolence. J Clin Sleep Med. 2022 May 1;18(5):1395-1403.
4. Dauvilliers Y, Evangelista E, Barateau L, et al. Measurement of symptoms in idiopathic hypersomnia: The Idiopathic Hypersomnia Severity Scale. Neurology. 2019 Apr 9;92(15):e1754-62.
5. Honda M, Kimura S, Sasaki K, et al. Evaluation of pathological sleepiness by Multiple Sleep Latency Test and 24-hour polysomnography in patients suspected of idiopathic hypersomnia. Psychiatry Clin Neurosci. 2021 Apr;75(4):149-51.
6. Bogan RK, Fuller DS, Whalen M, et al. A minimal clinically important difference for the sleep inertia visual analog scale in idiopathic hypersomnia. J Clin Sleep Med. 2025 Mar 26. Epub ahead of print.
7. Mantantzis K, Campos V, Darimont C, Martin FP. Effects of dietary carbohydrate profile on nocturnal metabolism, sleep, and wellbeing: a review. Front Public Health. 2022 Jul 13;10:931781.
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