Specialized Techniques

Chapter 14


Specialized Techniques



14A


Multiple Sleep Latency Testing



The most common indication for referring a patient for laboratory assessment is excessive daytime sleepiness (EDS), although sleep onset and sleep maintenance insomnia is the most common complaint in the general population. The initial step in assessment of a patient with EDS is detailed sleep and other histories, and physical examination. For assessment of persistent sleepiness, the Epworth Sleepiness Scale (ESS) is often used to assess a general level of sleepiness. This is a subjective propensity to sleepiness assessed by the patient under eight situations on a scale of 0 to 3, with 3 indicating a situation when chances of dozing off are highest. The maximum score is 24, and a score of 10 suggests the presence of EDS. This test has been weakly correlated with multiple sleep latency test (MSLT) scores. The ESS and MSLT, however, test different types of sleepiness. MSLT tests the propensity to sleepiness objectively, and ESS tests the general feeling of sleepiness or subjective propensity to sleepiness. The Stanford Sleepiness Scale is a 7-point analog scale to measure subjective sleepiness, but it does not measure persistent sleepiness. Visual Analog Scale is the other scale used to assess alertness and well-being, in which subjects indicate their feelings of alertness at an arbitrary point on a line of 0- to 100-mm scale, with 100 being the maximum sleepiness and 0 being the most alert.



Technique of Multiple Sleep Latency Test


The MSLT has been standardized and includes several general and specific procedures. The general procedures before the actual recording include keeping a sleep diary for 1 to 2 weeks before the test, which records the information about bedtime, time of rising, napping, and any drug use. The test is preceded by an overnight polysomnographic (PSG) study, and MSLT is scheduled about 2 to 3 hours after the conclusion of the overnight PSG study. The actual test consists of four to five opportunities for napping at 2-hour intervals, and each recording session lasts for 20 minutes. Between tests subjects must remain awake. The subjects must not smoke for 30 minutes before lights are turned off. Physiological calibrations (i.e., grit teeth, blink your eyes, look up, look down, look to the right, look to the left, open your eyes, and close your eyes) are then performed, and the patient is instructed to relax and fall asleep, and the lights are turned off. The test must be conducted in a quiet, dark room. The specific recording includes three or more channels of electroencephalography (EEG), submental electromyography (EMG), and electro-oculography (EOG) recordings. Three to four channels of EEG (F3-A2, C3-A2, 01-A2, and C4-A1) are recommended to document alpha activity in relaxed wakefulness in adults and its disappearance at sleep onset.


The measurements include average sleep-onset latency and the presence of sleep-onset rapid eye movements (SOREMs). If no sleep occurs, then the test is concluded 20 minutes after lights are turned off. The time from lights out to the first onset of any stage of sleep is defined as sleep latency. The test is terminated 15 minutes after the first 30-second epoch of any stage of sleep. If the finding is indefinite, then it is better to continue the test than to end it prematurely. Mean sleep latency is calculated from the sum of the latency to sleep onset for each of the four to five naps. Mean sleep latency of less than 8 minutes is consistent with pathological sleepiness. A mean sleep latency of 8 to 10 minutes is consistent with mild sleepiness. The occurrence of rapid eye movement (REM) sleep within 15 minutes of sleep onset is defined as SOREMs.


Repeat MSLT is required if the patient is strongly suspected of having narcolepsy but did not show the characteristic findings, as may be seen in a certain percentage of narcolepsy patients. MSLT may not be diagnostic in the initial test, and the diagnostic yield increases after the second test. The other situation for repeating MSLT is when the findings are ambiguous and the sleep onset or REM sleep cannot be adequately interpreted. Finally, if the MSLT guidelines have not been followed, the test results may be invalid.



Indications for Multiple Sleep Latency Test


The American Academy of Sleep Medicine (AASM) Standards of Practice Committee recommended indications for MSLT. Narcolepsy is the single most important indication for performing the MSLT (Fig. 14A.1). A mean sleep latency of less than 8 minutes combined with SOREMs in two or more of the four to five recordings during MSLT is strongly suggestive of narcolepsy, although REM sleep dysregulation and circadian rhythm sleep disorders may also lead to such findings.



In patients with upper airway obstructive sleep apnea syndrome (OSAS), the MSLT is not routinely indicated in the initial evaluation and diagnosis or in assessment of change following treatment with nasal continuous positive airway pressure (CPAP). However, those patients previously diagnosed with OSAS or other sleep-related breathing disorder, periodic limb movement disorder, or mood disorders who continue to have excessive sleepiness despite optimal treatment may require evaluation by the MSLT to exclude associated narcolepsy. The coexistence of OSAS and narcolepsy is well known.


An MSLT is indicated in patients suspected of having idiopathic hypersomnia; in this condition the MSLT findings will be consistent with pathological sleepiness but without SOREMs.


In patients with medical and neurological disorders (other than narcolepsy), insomnia, or circadian rhythm disorders, the MSLT is not routinely indicated for evaluation of sleepiness.


The following are the recommended indications for repeat MSLT: (1) extraneous circumstances or inappropriate conditions affecting the initial MSLT, (2) presence of ambiguous or uninterpretable findings, (3) initial MSLT without polygraphic confirmation in a patient suspected of having narcolepsy.



Reliability, Validity, and Limitation of the Multiple Sleep Latency Test


The sensitivity and specificity of the MSLT in detecting sleepiness have not been clearly determined. The test-retest reliability of the MSLT, however, has been documented in both normal subjects and patients with narcolepsy. In subjects with sleepiness caused by circadian rhythm sleep disorders, sleep deprivation, and ingestion of hypnotics and alcohol, pathological sleepiness has been validated by the MSLT. However, there is poor correlation between the MSLT and ESS. The patient’s psychological and behavioral state also interferes with the MSLT results. If the patient suffers from severe anxiety or psychological disturbances causing behavioral stimulation, MSLT may not show sleepiness even in a patient complaining of EDS. Day-to-day variability in the degree of sleepiness and an inability to cooperate or understand instructions are other factors for unreliability. Furthermore, pathological sleepiness with two or more SOREMs may occasionally be seen in other conditions (e.g., OSAS, REM sleep dysregulation, circadian rhythm sleep disorders). In addition, the MSLT measures propensity to fall asleep in an environment (e.g., sleep laboratory) conducive to sleep but not in other conditions (e.g., work or driving). One should also beware of false-positive and false-negative test results. In one study only 80% of cases of narcolepsy were diagnostically positive on the initial MSLT. Repeat studies showed positive results in 85% to 90%, but a small percentage of narcolepsy-cataplexy cases may not show two or more s even on repeated studies.




Technique of the MWT


The MWT protocols require four trials at 2-hour intervals to test an individual’s ability to stay awake. Based on studies published in the peer-reviewed literature, the Standards of Practice Committee of the AASM recommended the MWT 40-minute protocol. Unlike the MSLT, the MWT does not require prior overnight polysomnography. The test is performed about 1½ to 3 hours after the individual’s usual wake-up time. The recording montage is similar to that used for the MSLT. The patient calibrations before each test are similar to those used for the MSLT. Before the beginning of the recording the patients are asked to sit still in bed with a back and headrest and remain awake as long as possible. They are not allowed to read, use headphones to listen to music, use a mobile phone, watch television, or use any digital device to read during each trial of 40 minutes. Sleep onset is defined as the time between lights off in the beginning of the recording and the onset of three consecutive epochs of stage 1 non-REM (NREM) or one epoch of any other stage of sleep. The test should be terminated after sleep onset or after 40 minutes if no sleep occurs. A mean sleep latency (the arithmetic mean of the four trials) of less than 8 minutes is considered abnormal as recommended by the Standards of Practice Committee of the AASM; values greater than this but less than 40 minutes are of uncertain significance.




Bibliography



Aldrich, M. S. Sleep Medicine. New York: Oxford University Press; 1999.


Arand, D., Bonnet, M., Hurwitz, T., et al. The clinical use of the MSLT and MWT. Sleep. 2005; 28:123–144.


Carskadon, M. A., Dement, W. C., Mitler, M., et al. Guidelines for the multiple sleep latency test MSLT: A standard measure of sleepiness. Sleep. 1986; 9:519–524.


Chervin, R. Assessment of sleepiness. In Chokroverty S., Montagna P., Allen R. P., Walters A. S., eds. : Sleep and Movement Disorders, 2nd ed, New York: Oxford University Press, 2013.


Doghramji, K. The maintenance of wakefulness test. In: Chokroverty S., ed. Sleep Disorders Medicine: Basic Science, Technical Considerations and Clinical Aspects. 3rd ed. Philadelphia: Saunders/Elsevier; 2009:224–228.


Littner, M. R., Kushida, C., Wise, M., et al. Practice parameters for clinical use of the multiple sleep latency tests and the maintenance of wakefulness test. Sleep. 2005; 28:113–121.



14B


Actigraphy



An actigraph, also known as an actometer or actimeter, monitors body movements and other activities continuously for days, weeks, or even months. This can be worn on the wrist or alternatively on the ankle for recording arm, leg, and body movements. An actigraph uses piezoelectric sensors that function as accelerometers to record acceleration or deceleration of movements rather than the actual movement. The mechanical movements are converted into electrical signals, which are then sampled every tenth second over a predetermined time or epoch and then retrieved and analyzed in a computer. The principle of analysis is based on the fact that increased movements (as indicated by black bars in the actigraph) are seen during wakefulness in contrast to markedly decreased movements or no movements (as indicated by the white area interrupting the black bars) during sleep, although normal physiological body and limb movements and postural shifts during sleep will cause interruptions (black bars) of the white background (Fig. 14B.1). Several actigraph models are in the development stage to carefully regulate the sampling frequencies and duration, filters, sensitivities, and dynamic range to detect and quantify periodic limb movements in sleep (PLMS), but no generally accepted standardized technique of quantifying and identifying PLMS that differentiates them from other movements (e.g., those resulting from parasomnias, nocturnal seizures, and other dyskinesias) is currently available. Two of these devices (i.e., Actiwatch and PAM-RL) showed a reasonable correlation with PLMS observed with PSG study. Further validation studies in a large number of patients are needed before these can be used reliably to detect and quantify PLMS. Currently several devices are available (e.g., ambulatory monitoring, Actiwatch, PAM-RL) along with appropriate software, with or without light or position sensors, to determine if the subject is sitting, lying, or upright. These devices can provide a direct assessment of the amount of activity or body movement at the site of attachment of the device. Studies have been conducted using actigraph and PSG recordings simultaneously to validate the ability of the actigraph to distinguish sleep from wakefulness. Computer algorithms are available for automatic sleep-wake scoring; however, visual inspection of the raw data is necessary. The reliability and validity of the data are available only for a specific actigraph model; no universally validated data are available. There is poor agreement between sleep characteristics obtained by actigraphy and subjective data from a sleep diary. Actigraphs can differentiate indirectly sleep from wakefulness (see Fig. 14B.1) but cannot differentiate REM from NREM sleep and cannot identify different NREM sleep stages. Actigraphs and sleep logs are complementary.




Indications for Actigraph


The AASM Standards of Practice Committee made the following recommendations for actigraph:



• Actigraph may be a useful adjunct to history, physical examination, and sleep logs in patients with insomnia, including paradoxical sleep (sleep state misperception) and inadequate sleep hygiene (Figs. 14B.2 to 14B.7), and circadian rhythm sleep disorders (Figs. 14B.8 to 14B.13).








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FIGURE 14B.7 Wrist actigraph from a 52-year-old psychologist with type I Arnold-Chiari malformation, who presented with sleep difficulties because of repeated awakenings and excessive daytime somnolence for 15 years (see Fig. 12.6). Overnight polysomnography showed rapid eye movement hypoventilation. The actigraph shows increased activity and periods of wakefulness during nighttime sleep (intrusions of black bars into white areas), irregular sleep onset at approximately 10:00 PM (day 1), midnight (day 2), 1:00 AM (day 3), 10:00 PM (day 4), 11:00 PM (day 5), 8:00 PM (day 6), and 10:00 PM (day 7), and variable wake-up times as indicated by sustained black bars. There are also many brief episodes of daytime somnolence (intrusions of white areas into black bars). On day 5 the actigraph was taken off during part of the waking period as indicated by abrupt onset of white area (no activity).





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FIGURE 14B.10 Delayed sleep phase.
The same patient as in Fig. 14B.9, treated with melatonin 1 mg per night (at 8 PM). Note in a free-running 6-day period an advance of 1 to 1½ hours for sleep onset and 2 hours for awakening except for occasional delays (third and fourth nights) during the weekend that were behaviorally induced.





• Actigraph may be a useful adjunct to detect the rest-activity patterns during modified portable sleep apnea testing.


• Actigraph is useful to document rest-activity patterns over days and weeks when a sleep log is not able to provide such data.


Although not adequately standardized, actigraph may have a role in patients with restless legs syndrome and PLMS (Figs. 14B.14 to 14B.16). It may also be useful to document objectively periodic hypersomnias as seen in patients with Kleine-Levin syndrome (Fig. 14B.17).






An important application of actigraphy is in field studies to assess sleep-wakefulness where PSG is not feasible.



Advantages of Actigraph Over Polysomnography


The advantages include the following: easy accessibility; inexpensive recording over extended periods for days, weeks, or even months; recording of 24-hour activities at all sites (home, work, or laboratories); usefulness in uncooperative and demented patients when laboratory PSG study is not possible; ability to conduct longitudinal studies during therapeutic intervention (behavioral or pharmacological treatment) in patients with insomnia; usefulness in sleep state misperception (see Fig. 14B.2); ability to document delayed or advanced sleep phase syndrome or non–24-hour circadian rhythm disorders, although sleep logs may suggest such a diagnosis; and documentation of excessive daytime sleepiness and repeated episodes of sleepiness (lasting more than a few minutes).

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Jul 16, 2016 | Posted by in NEUROLOGY | Comments Off on Specialized Techniques

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