Idiopathic Hypersomnia

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Distinguishing Primary Hypersomnia from Other Sleep Disorders

Idiopathic hypersomnia, also known as primary hypersomnia, is a sleep disorder characterized by excessive daytime sleepiness that has no identifiable cause. While the precise physiology of the disorder is still not clearly understood, it is believed to have its root in the central nervous system. A positive diagnosis of idiopathic hypersomnia will usually lead to treatment using stimulant medications.

Common Causes of Excessive Daytime Sleepiness

It can sometimes be normal to feel excessively sleepy during the day. New parents, college students, and shift workers will attest that in some circumstances, extreme sleepiness is expected. For this reason, it is important to distinguish between EDS and fatigue. Fatigue is the expected result of disturbed nocturnal sleep.

In the 2008 publication Clinical Manual for Evaluation and Treatment of Sleep Disorders, authors Reite, Weissberg and Ruddy explain that fatigue and sleepiness might be a symptom of certain lifestyle factors, or of an underlying physical or psychiatric issue. Of the many reasons that adults experience excessive daytime sleepiness, Reite et al list the following as having potential clinical significance:

  • sleep apnea, narcolepsy, or periodic hypersomnias
  • psychiatric or other medical disorders
  • limb movement disorders
  • drug or alcohol abuse
  • long natural sleep rhythms
  • insufficient nocturnal sleep

Excessive sleepiness that is not explained by other factors and that persists for a period of one month or more may indicate idiopathic hypersomnia.

Symptoms of Idiopathic Hypersomnia

Idiopathic hypersomnia is a poorly defined condition. In this article “Primary Hypersomnia,” Adrian Preda, MD writes that while narcolepsy has a well established pattern of features observable during clinical interviews and sleep studies, hypersomnia is more nebulous by nature(November 9, accessed March 2010.)

Idiopathic hypersomnia lacks the sleep paralysis, cataplexy, and sleep-onset rapid-eye movement (REM) associated with narcolepsy. Without these dramatic symptoms, it can be easy to overlook idiopathic hypersomnia or to explain it away as simple fatigue. There are, however, defining characteristics that distinguish hypersomnia from other causes of excessive daytime sleepiness.

According to Preda, symptoms include:

  • Deep sleep: Hypersomniacs sleep deeply, and experience a phenomenon known as sleep drunkenness upon awakening. Disorientation, confusion, lack of coordination and difficulty achieving full consciousness are typical of sleep drunkenness.
  • Prolonged sleep: In addition to sleeping very deeply, hypersomniacs sleep for a prolonged period of time, and experience extended periods of non-REM sleep.
  • Excessive daytime sleepiness: Periods of sleepiness that significantly disrupt daily activities are considered excessive.
  • Daytime lapses into microsleep: Brief naps lasting only a few seconds or minutes are common among hypersomnia patients. Patients may not even be aware of these episodes, making activities such as driving particularly hazardous.
  • Non-refreshing naps: During the day, patients will often fight sleep as long as possible. When hypersomniacs do nap, the sleep is not refreshing or restorative.

Sleep Disorder Diagnosis

The primary consultation with a sleep specialist will likely involve a detailed personal history. Reite et al outline an interview that delves into the patient’s daytime functioning, nocturnal sleep habits, and personal history. As the condition is thought to be at least partially hereditary, a thorough interview will also involve investigation of the sleep habits of parents, siblings, and possibly even children of the patient.

Additionally, the patient will be asked to grade hypothetical sleepiness. Given a particular scenario, such as watching a movie or waiting in a physician’s waiting room, patients are asked to rate their likelihood of falling asleep using one of two standardized scales.

Finally, if the physician concludes that the patient’s history is suggestive of idiopathic hypersomnia or another sleeping disorder, he or she will schedule a sleep study test, in which the patient’s brain waves and vital signs are monitored during sleep.

Treatment for Hypersomnia

Because the precise physiology of idiopathic hypersomnia is not fully understood, treatment of the disorder is usually limited to control of the symptoms. In most cases, this involves the use of stimulant medication to increase daytime alertness and reduce feelings of sleepiness.

Determining the best medication and the optimal dosage may take a while, but in most cases idiopathic hypersomnia can be effectively managed. While the process may seem like a long road, it is a worthwhile investment of time.


Preda, Adrian. “Primary Hypersomnia.” eMedicine from WebMD. 3 November 2009. Medscape.

Reite, Martin, Michael P. Weissberg and John Ruddy. Clinical Manual for Evaluation and Treatment of Sleep Disorders. Arlington: American Psychiatric Pub.