Evaluation of the patient with EDS

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A detailed history and physical examination are of key importance in evaluating the patient complaining of EDS. Important points of the sleep history that the clinician should document include, but are not limited to, total daily 24-hour sleep time, nightly and daily sleep and nap patterns, time to initial sleep onset, and number and duration of nocturnal awakenings. A sleep log in either narrative or graphical form may be used to characterize a patient's sleep further.

When reviewing a patient's sleep log in the workup of EDS, special attention is paid to the quantity, consistency, and continuity of reported sleep. The consistency of sleep-wake times provides insight into circadian and social pressures on the timing of sleep and may help identify causes of insufficient sleep. If the patient is unable to give a reliable history or nightly sleep times are in question, monitoring for several days with actigraphy (a wristwatch-like device that registers movement by the patient) may be useful in evaluating patterns of waking and sleep.

Thorough screening for primary sleep disorders includes assessment of the presence of snoring, witnessed apneas, symptoms of restless legs syndrome, periodic limb movements, and restless sleep or non-refreshing sleep. Medical conditions and alcohol or drug use can be significant contributors to EDS; if any of these are suspected, appropriate evaluation should ensue. Any chronic sedating medications should also be noted.

If a thorough history and physical examination raises suspicion of disorders such as periodic limb movements, obstructive sleep apnea, nocturnal seizure, or parasomnia, then nocturnal polysomnography (PSG) - overnight sleep study - may be indicated to either rule out sleep disturbances or to quantify their severity. This is typically related to sleep disorders that produce sleep fragmentation or sleep inefficiency including sleep-related breathing disorders, periodic limb movement disorder, REM sleep behavior disorder, other sleep-related movement disorders, parasomnias, or nocturnal seizures.

Several questionnaires have been developed to help clinicians screen for and evaluate patients for sleepiness and its impact on daily living. These questionnaires include, among others, the Epworth sleepiness scale (ESS) [4], the Stanford sleepiness scale [5], and the sleep-wake activity inventory [6]. The ESS is the most commonly used questionnaire because of its ease of use and its well-documented validity as a clinically relevant measure of sleepiness in conditions of pathological EDS [7-9].

Although ESS scores are not necessarily representative of true levels of sleepiness and the questionnaire is neither highly specific nor sensitive for the existence of pathological sleepiness, the ESS serves as a useful screen for patients who are severely sleepy [10]. In our experience it has also been a simple, quick, and low-cost method for following patient response to treatment. Given its ease of use and the high prevalence of sleepiness among the general population, we recommend administering the ESS in patients with complaints of excessive sleepiness [4].

The multiple sleep latency test (MSLT) provides a more objective quantification of sleepiness than questionnaires by objectively measuring the propensity to fall asleep. Please see Chapter 3: Neurophysiology and neuroimaging of human sleep for a more detailed review of this procedure. Essentially, this test measures the capacity to fall asleep and propensity for both early sleep onset and early rapid eye movement sleep (REM) onset. The MSLT has specificity limitations due to the variety of conditions that can produce an abnormal result. Nevertheless, following a thorough clinical evaluation, the MSLT is the primary tool for confirming some of the hypersomnias [1,11]. The MSLT consists of four or five 20-minute polysomno-graphically monitored daytime nap opportunities separated by 2-hour intervals; for the nap opportunities, the patient is reclined in a sleep laboratory bed in a dark room with instructions to fall asleep. The primary assessments made by the MSLT are the rapidity of sleep onset, which correlates to degree of sleepiness, and the occurrence of REM sleep if sleep occurs during the nap opportunity. REM sleep episodes (a period of sleep during which dreams occur) at or close to sleep onset are known as sleep-onset REM periods (SOREMPs). Sleep latencies in normal adults are often between 10 and 20 minutes; pathological sleepiness is manifested by a latency of less than 8 minutes [11,12]. The MSLT should be performed only after the patient has received an adequate amount of nocturnal sleep (approximately 8 hours per night for the typical adult) for a period of at least 2 weeks and immediately following a nocturnal poly-somnogram to exclude other causes of EDS due to either sleep fragmentation or insufficient sleep. If the polysomnogram is positive for other causes of EDS, these conditions must be adequately treated before an evaluation of EDS with MSLT is pursued. Practicing clinicians should also be aware that commonly prescribed antidepressants can have profound effects on the MSLT by suppressing potential SOREMPs. Therefore, the decision regarding whether such medications should be tapered prior to MSLT should be made cooperatively with the patient, and include the risks of potentially worsening the psychiatric illness versus a confounded MSLT.

The maintenance of wakefulness test (MWT) is another diagnostic test in the sleep laboratory. Rather than evaluating the propensity to fall asleep (like the MSLT), the MWT assesses the capacity to maintain wakefulness while sedentary in a setting conducive to sleep during the patient's regular waking hours. This test is not generally used in the evaluation of hyper-somnias of central origin, rather it is used for safety assessment to evaluate the impact of treatment for sleep disorder-related EDS in specific occupations such as heavy equipment operators or airline pilots.

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