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Ask the Doctor: Narcolepsy vs Idiopathic Hypersomnia

Ask the Doctor: Narcolepsy vs Idiopathic Hypersomnia:

What’s the Difference?

My 9-year-old son recently was diagnosed with IH but can’t exclude narcolepsy. We got a second opinion and the doctor agreed. I don’t understand why they don’t have a definitive answer. The doctors told me to not to worry about narcolepsy vs. hypersomnia. Can anyone help me understand the difference? And is it possible to have IH and beginning stages of narcolepsy?
Dr David Plante presenting at the Beyond Sleepy in the Mile High City Conference
Both narcolepsy and idiopathic hypersomnia (IH) are considered central disorders of hypersomnolence (CDH). They share similarities, most important of which is the requirement that patients with both disorders must experience significant excessive daytime sleepiness. From a diagnostic standpoint, sleep medicine uses the multiple sleep latency test (MSLT), a repeated nap study performed after polysomnography (PSG; an overnight sleep test), to help identify and characterize central disorders of hypersomnolence. One of the primary results of these tests used to determine whether a patient has narcolepsy or IH is based on the number of sleep onset REM periods (SOREMPs), during which individuals go into REM sleep much faster than is typical. Patients with narcolepsy have 2 or more SOREMPs on PSG/MSLT testing, where patients with IH do not.

There are differences in other clinical symptoms experienced by patients that can be used to help clarify whether a person has narcolepsy or IH. For example, patients with IH often sleep excessive amounts of time and have severe difficulty waking up after sleeping (i.e. excessive sleep inertia). Patients with narcolepsy frequently do not sleep excessive amounts of time, and may find brief naps refreshing. Many patients with narcolepsy also experience symptoms related to REM sleep instability such as sleep paralysis (waking from sleep in a paralyzed state) and hallucinations around sleep onset/offset, thought to be due to inappropriate combinations of REM sleep and waking brain function. In addition, some patients with narcolepsy experience cataplexy, the sudden loss of muscle tone in response to emotions such as laughter. Cataplexy is almost never seen outside of narcolepsy, and thus when patients have this symptom, there is high suspicion that the patient does indeed have narcolepsy.

Sometimes, the clinical history and results of PSG/MSLT testing do not neatly align. Although I do not have the specifics in the case of your son to comment definitively, it is certainly possible that the results of his sleep testing have shown he is pathologically sleepy consistent with IH, but did not have enough SOREMPs to be diagnosed with narcolepsy. He may also have clinical symptoms that are more suggestive of a narcolepsy diagnosis than IH, which is why there is some ambiguity around the diagnosis. Sometimes retesting can help clarify the diagnosis, but not always. Because initial treatment of both narcolepsy and IH often involves stimulants, oftentimes treatment is initiated for practical reasons to try to improve the patient’s symptoms, since the precise diagnosis may not alter initial clinical management, particularly in the early stages of treatment.

David T. Plante, M.D.
Assistant Professor, Department of Psychiatry
Program Director, Sleep Medicine Fellowship
University of Wisconsin School of Medicine and Public Health


Glossary of terms:

Central Disorders of hypersomnolence (CNS): As defined by the ICSD-3 rd –Include Narcolepsy Type 1, Narcolepsy Type 2, Idiopathic Hypersomnia, and Kleine- Levin Syndrome. They also include hypersomnolence caused by a medical disorder, medication or substance, psychiatric disorder and insufficient sleep disorder.

Rapid Eye Movement (REM) sleep: One of the two basic states of sleep. REM sleep, also known as dream sleep, is characterized by rapid eye movements, and more irregular breathing and heart rate compared to NREM sleep, the other basic state of sleep.

Sleep Onset REM Period (SOREMP): REM periods within 15 minutes of sleep onset, considered to support the diagnosis of narcolepsy.

Sleep Inertia: Feelings of grogginess and sleepiness that occur upon awakening that can result in impaired alertness and may interfere with the ability to perform mental or physical tasks.

Sleep Paralysis: involves the temporary inability to move, speak, or take a deep breath while falling asleep or waking up.

Hypnagogic or hypnopompic hallucinations: Sensory experiences involving the apparent perception of something that is not present, that occur at the transition from wakefulness to sleep (hypnagogic) or from sleep to wakefulness (hypnopompic). These hallucinations are typically visual in nature, but can affect other forms of sensation such as hearing or sense of touch.


 

Disclaimer for Ask The Doctor: The medical information provided is meant for educational purposes only and not as a substitute for professional medical care or advise.  Questions about a personal health condition should be discussed with your healthcare professional.

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Ask The Doctor: Idiopathic Hypersomnia vs Type 2 Narcolepsy

Question: Is there an overlap between idiopathic hypersomnia and type 2 narcolepsy?

Answer: The short answer to this question is yesThe only way to definitively distinguish idiopathic hypersomnia (IH) from type 2 narcolepsy (T2N) is the number of sleep-onset REM periods (SOREMPs) on diagnostic testing. However, in a group patients with IH, T2N, or symptoms of excessive sleepiness who had normal results on a single Multiple Sleep Latency Test (MSLT), researchers showed that the diagnosis changed more than half of the time when the MSLT was repeated1—this means that some patients initially diagnosed with IH may later have a diagnosis of T2N, and vice versa, or they may have no sleep disorder diagnosed and then have T2N or IH on another MSLT, and, again, vice versa. In the general population as a whole (ie, not just those who are sleepy), the presence or absence of SOREMPs on repeated MSLTs is also quite variable,2 suggesting that this may not be the best feature to use in discriminating among diseases. Indeed, prominent narcolepsy researchers have concluded that the presence of “2 or more sleep-onset REM periods [eg, on the MSLT] does not appear to have any specific pathognomonic significance.”3

The idea that T2N can overlap in some of its clinical symptoms with IH, as opposed to MSLT features (that is, “signs” of REM sleep on napping), was first proposed by the Czech sleep neurologist Bedrich Roth.4 In noting that many patients with T2N experienced long sleep periods and sleep inertia, he proposed that both IH and T2N might be considered as part of the same phenotypic spectrum or continuum of “disease.” Roth’s interpretation found further support in his recognition of a potential common heritability in these primary hypersomnias (that is, individuals with T2N and others with IH often have family members with the other condition).

Additional support for concluding that T2N and IH are more alike than they are different comes from four independent sources and lines of inquiry.

  • First, nearly 20% of people with T2N sleep continuously for long periods (for example, for 11 out of 24 hours, thus, meeting the criteria for a diagnosis of IH).5
  • Second, bioactivity that enhances the inhibitory function of GABA has been found in the cerebrospinal fluid (CSF) of many people with T2N and people with IH, whereas the same CSF samples exhibit normal levels of hypocretin.6
  • Third, a substantial proportion of people with T2N and people with IH whose sleepiness/hypersomnia does not respond to traditional wake-promoting medications and whose CSF samples share an ability to excessively enhance GABA function respond positively to medications that are intended to suppress this enhancement (for example, flumazenil and clarithromycin).6,7
  • Fourth, results of a process called “cluster analysis” suggest that symptoms of IH (without long sleep time) and T2N are more similar than they are different.8 In cluster analysis, symptoms are compared among people while ignoring their official diagnosis, and new categories are created based on which symptoms or signs tend to occur together. In this study, three new “clusters” of disease were created:
    • People with T1N
    • People with IH with long sleep times (based on ICSD-2 criteria)
    • People with either T2N or IH without long sleep times

 

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;9(8):789-795. PMID: 23946709.
2          Goldbart A, Peppard P, Finn L, et al. Narcolepsy and predictors of positive MSLTs in the Wisconsin Sleep Cohort. Sleep. 2014;37(6):1043-1051. PMID: 24882899.
3          Singh M, Drake CL, Roth T. The prevalence of multiple sleep-onset REM periods in a population-based sample. Sleep. 2006;29(7):890-895. PMID: 16895255.
4          Roth B. Narcolepsy & Hypersomnia. Basel, Switzerland: S. Karger Ag; 1981.
5          Vernet C, Arnulf I. Narcolepsy with long sleep time: a specific entity? Sleep. 2009;32(9):1229-1235. PMID: 19750928.
6         Trotti LM, Saini P, Koola C, LaBarbera V, Bliwise DL, Rye DB. Flumazenil for the treatment of refractory hypersomnolence: clinical experience with 153 patients. J Clin Sleep Med. 2016 [Epub ahead of print]. PMID:26149554.
7         Trotti LM, Saini P, Bliwise DL, Freeman AA, Jenkins A, Rye DB. Clarithromycin in gamma-aminobutyric acid-related hypersomnolence: a randomized crossover trial. Ann Neurol. 2015;78(3):454-65. PMID:26094838
8         Sonka K, Susta M, Billiard M. Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis. Sleep Med. 2015;16(2):225-231. PMID: 25576137.

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There’s A Doctor in the Hypersomnia House

A few weeks ago, we launched our latest Hypersomnia Foundation program – Ask the Doctor. We thank everyone who has sent questions and encourage you to send your questions to atd@hypersomniafoundation.org.

Some of the questions that we received made us think about the language that we use when talking about sleep disorders. I know what I mean when I use a word, and you know what that word means to you, but unless our words mean the same thing to both of us, unless we use a common language, we are not hearing clearly what the other person is saying. I might say I have hypersomnia and mean that I am sleepy, but to you it means that you sleep for a long time. Language in general and the language of sleep disorders not only has changed over the years, but also will continue to change. So, today, thanks to your questions, we will discuss a few of these terms and provide a little background on why there is so much confusion.

Question: What do we mean when we say hypersomnia?
Answer: Hypersomnia means literally too much sleep. The definition of what is “too much” sleep can be debated but has been defined at various times for medical purposes as more than 10 to 11 hours per day. In current medical use, the word hypersomnia is also used to mean simply excessive sleepiness, regardless of sleep time.

Question: What is the difference between hypersomnia and hypersomnolence?
Answer: The Hypersomnia Foundation uses the term hypersomnia to mean the condition of too much sleep. Likewise, the International Classification of Sleep Disorders, third edition, reserves the term hypersomnia to mean the specific syndrome of idiopathic hypersomnia and the term hypersomnolence for the more general condition of excessive sleepiness.

Question: What are the differences between the terms sleepiness and fatigue?
Answer: Doctors have struggled to define and measure what is meant by the word sleepiness, as compared with other commonly used words such as tired, fatigued, and lack of energy. In general, doctors define sleepiness as the experience of being more likely than most people to take naps during the day, sleep for long periods at night, or fall asleep at times that it is problematic to do so (for example, while driving, at work, or during a conversation). In contrast, fatigue is defined as a state of having low energy or having trouble remaining on the same task but not necessarily falling asleep or sleeping too much.

Despite this distinction, it has turned out to be very challenging to measure sleepiness and fatigue in clinical settings. Part of this challenge is reflected in the fact that individuals who have sleep disorders do not necessarily experience these as completely different states (that is, patients with hypersomnolence might experience both sleepiness and fatigue, as defined above). Further, they do not typically use words to describe their symptoms that fit with the above schema.

A classic research study of patients with sleep apnea (who were sleepy because they did not breathe properly at night) showed that patients were sleepy based on their ability to fall asleep quickly during a Multiple Sleep Latency Test (MSLT) but were more likely to say that they had fatigue, tiredness, or lack of energy than sleepiness.1 In this study, when asked to choose only one response to describe their symptom, about 40% of subjects chose lack of energy and only about 22% chose the term sleepiness.

Determining optimal measures of fatigue has not been any easier; researchers use no fewer than 8 different scales to measure fatigue. The Multidimensional Fatigue Inventory attempts to further divide fatigue into distinct parts such as general fatigue, physical fatigue, and mental fatigue, as well as reduced overall activity versus reduced motivation.

1. Chervin RD. Sleepiness, fatigue, tiredness, and lack of energy in obstructive sleep apnea. Chest 2000;118:372-9.

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