Multiple Sleep Latency Testing (MSLT)
Multiple Sleep Latency Testing (MSLT) is also often called a nap study. It is similar in set-up to the polysomnogram (PSG) described above. These studies will typically be done after an initial overnight PSG study. After waking up, the individual will have scheduled nap times throughout the day. These typically occur every two hours. Generally, the patient is put to bed and allowed to lie there for 20 minutes with the goal of falling asleep. The technician will monitor for the onset of sleep and, in particular, REM sleep. After 20 minutes, the person will be awakened or told that his time for a nap has ended. Then, in 2-hour intervals, this process is repeated. Typically these will occur over a 10-hour period. These tests are useful for identifying excessive daytime sleepiness. This may be present in numerous disorders, such as sleep apnea, idiopathic hypersomnia (excessive sleepiness without a cause), and narcolepsy. In particular, the early onset of REM in these sleep periods may suggest narcolepsy.
Actigraphy
Actigraphy is the measurement of activity with the use of a small, wristwatch-sized device. This device monitors movement and can be used to assess sleep-wake cycles, or circadian rhythms, over an extended period of time. They may be worn for weeks or even months. They help determine whether disruptions in the sleep-wake cycle exist, as may occur in circadian rhythm disorders such as advanced sleep phase syndrome, delayed sleep phase syndrome, or even with insomnia. These results are often correlated with a sleep diary.
Sleep Diary
The sleep diary, or sleep log, is sometimes useful for assessing circadian rhythm disorders or insomnia, especially in adjunct to actigraphic data. These may also be used to assess sleep problems among children. In general, they are a paper record and document sleep and wakefulness over a period of weeks and months. The bedtimes and wake-times are noted. Any periods of wakefulness during the night or naps during the day are also documented. Sometimes the use of caffeine, alcohol, or medications may also be recorded.
Home Study
Finally, most individuals recognize that they sleep far better at home than they might in a sleep center. This is certainly true, and many are pushing to develop technologies that may allow home assessment of sleep disorders. These may include limited studies that monitor basic parameters of sleep, such as oxygen levels, heart rates, and the movement of the chest and abdomen with special belts. Some titration studies can be conducted at home through the use of the CPAP machine, such as auto-titration studies.
In addition, new technologies are being researched that may lead to other monitoring. In general, these new technologies are in their infancy and the data may not be reliable as the current gold standard of diagnosis which is the overnight polysomnogram performed in an accredited sleep center.
Sources:
Littner, M. et al. Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test. Sleep 2005; 28:113.
Mitler, M. and Miller, J. Methods of testing for sleepiness. Behav Med 1996; 21:171.
Stepanski, E. et al. Effects of sleep deprivation on daytime sleepiness in primary insomnia. Sleep 2000; 23:215.
