Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompassing several sleep disorders where increased sleep is a symptom, or as a symptom of another underlying disorder like narcolepsy, circadian rhythm sleep disorder, sleep apneaoridiopathic hypersomnia.
Some persons with EDS, including those with hypersomnias like narcolepsy and idiopathic hypersomnia, are compelled to nap repeatedly during the day; fighting off increasingly strong urges to sleep during inappropriate times such as while driving, while at work, during a meal, or in conversations. As the compulsion to sleep intensifies, the ability to complete tasks sharply diminishes, often mimicking the appearance of intoxication. During occasional unique and/or stimulating circumstances, a person with EDS can sometimes remain animated, awake and alert, for brief or extended periods of time. EDS can affect the ability to function in family, social, occupational, or other settings.[1][2] A proper diagnosis of the underlying cause and ultimately treatment of symptoms and/or the underlying cause can help mitigate such complications.[3] According to the National Sleep Foundation, around 20 percent of people experience excessive daytime sleepiness.[4]
An adult who is compelled to nap repeatedly during the day may have excessive daytime sleepiness; however, it is important to distinguish between occasional daytime sleepiness and excessive daytime sleepiness, which is chronic.
A number of tools for screening for EDS have been developed. One is the Epworth Sleepiness Scale which grades the results of a questionnaire with eight questions referring to situations encountered in daily life. The ESS generates a numerical score from zero (0) to 24 where a score of ten [10] or higher may indicate that the person should consult a specialist in sleep medicine for further evaluation.[10][11][12]
Another tool is the Multiple Sleep Latency Test (MSLT), which has been used since the 1970s. It is used to measure the time it takes from the start of a daytime nap period to the first signs of sleep, called sleep latency. Subjects undergo a series of five 20-minute sleeping opportunities with an absence of alerting factors at 2-hour intervals on one day. The test is based on the idea that the sleepier people are, the faster they will fall asleep.[13][14]
The Maintenance of Wakefulness Test (MWT) is also used to quantitatively assess daytime sleepiness. This test is performed in a sleep diagnostic center. The test is similar to the MSLT as it also relies on a measurement of initial sleep latency. However, during this test, the patient is instructed to try to stay awake under soporific conditions for a defined time.[15][16]
The use of Electroencephalography (EEG) readings is essential for the objective diagnosis of EDS. The initial sleep latency employed in the MSLT and the MWT is mainly derived from EEG recordings.[16] Moreover, power characteristics in the alpha-band of resting-state EEG readings, correlating with somnolence, also showed a correlation with the presence of EDS.[17][18][19]
^Valentino, RM; Foldvary-Schaefer, N (August 2007). "Modafinil in the treatment of excessive daytime sleepiness". Cleveland Clinic Journal of Medicine. 74 (8): 561–6, 568–71. doi:10.3949/ccjm.74.8.561. PMID17708127.
