Central Disorders of Hypersomnolence (Narcolepsy and Idiopathic Hypersomnia)

Overview

Patients with narcolepsy experience excessive daytime sleepiness that impacts their ability to fully participate in school, at work, or in their social or family life due to sleepiness. Patients may have an overwhelming urge to sleep or nap, and they often feel refreshed after relatively short naps. They typically get a normal amount of sleep, although their sleep may be fragmented or feel poor-quality.

Symptoms

Narcolepsy is caused by an abnormality in REM sleep (dream sleep) and symptoms that are associated with narcolepsy involve abnormal intrusions of REM sleep features into wake: for example, sleep-related hallucinations, sleep paralysis, or vivid dreams and dream-reality confusion. These symptoms can also occur in people without a sleep disorder.

Some patients with narcolepsy also experience cataplexy (narcolepsy, type 1) which is loss of muscle tone triggered by emotion, typically laughter or anticipation. Cataplexy can be generalized or partial and isn’t associated with any loss of consciousness. This muscle weakness typically improves within seconds to minutes.

Patients with idiopathic hypersomnia (IH) often describe excessive daytime sleepiness, prolonged sleep duration (more than 10-11 hours of sleep nightly), and severe difficulty waking up in the morning (sleep inertia). In contrast to narcolepsy, patients with IH often describe long, unrefreshing daytime naps. Another common symptom of IH is “brain fog,” a feeling of cognitive clouding during the day. Klein-Levin syndrome is a rare disorder of cyclic hypersomnia.

Diagnosis

Evaluation of central disorders of hypersomnolence includes sleep testing in the sleep lab (polysomnography, PSG) followed by a multiple sleep latency test (MSLT). The overnight PSG excludes other causes of severe daytime sleepiness, like sleep apnea. The multiple sleep latency test involves a series of five 20-minute nap opportunities throughout the day. The amount of time it takes to fall asleep combined with the presence of REM sleep determines the final diagnosis.

Because the results of the MSLT can be impacted by habitual delayed sleep times or sleep deprivation, patients undergoing this evaluation should keep a sleep diary for two weeks before this test and make every effort to sleep for at least seven hours/night every night for two weeks before the test.

The results of the MSLT are also impacted by certain medications or substances, so patients may be counseled to taper off medications before coming in. A urine toxicology screen is also routinely obtained on the night of the sleep study to inform interpretation of the sleep study results.

The MSLT is a very good test for narcolepsy, but it is less sensitive for idiopathic hypersomnia. As a result, patients with clinical symptoms of idiopathic hypersomnia who report regularly prolonged sleep duration (average sleep duration more than 11 hours/night) may instead be referred for an extended or unrestricted sleep study.

Additional diagnostic tests for narcolepsy may include a blood test for HLA-DQB1*0602.