ACNS clinical controversy: MSLT and MWT have limited clinical utility.

The Multiple Sleep Latency Test (MSLT) and the Maintenance of Wakefulness Test (MWT) are two commonly used laboratory-based objective tests to measure sleepiness and alertness, respectively. Data suggest both are extremely sensitive tests when measuring the effects of sleep deprivation within subjects, but are less sensitive for confirming sleepiness and response to treatment in groups of patients with different sleep disorders. Inconsistent and even sometimes paradoxical test results may be partly explained by data that show the MSLT and MWT are not selectively sensitive to either sleepiness or alertness, but sensitive to both the sleep and the arousal systems. Sleep latencies seen on both the MSLT and MWT are affected to varying degrees by a myriad of internal and external influences that can alter what we would prefer each test to show. If we continue to use these tests to measure sleepiness or alertness in patients with different sleep disorders, we need to understand more about the nature and impact of different sources of internal and external arousal so that we can better control the test environment. Improved understanding of the determinants of sleep onset is essential because excessive sleepiness has important consequences for both individuals and society.