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Table 143-4 Comparison between Tests for Evaluating Sleepiness
Physiologic Sleepiness
Manifest Sleepiness
Vigilance and performance
Yes §
ESS Yes Yes Yes
SSS No Yes Yes
POMS Yes Yes Yes
*Standard protocol described in an American Academy of Sleep Medicine Practice Parameter: Test involves 4 to 6 test sessions per day,
at 2-hour intervals. Test sessions are sometimes scheduled at shorter intervals (e.g., for children); however, this practice is not
recommended by the authors.
Assuming that the subject is not overwhelmingly sleepy, attempting to remain awake can undermine the test result.
Assuming that the subject is physiologically sleepy, not attempting to remain awake will make it appear that overwhelming sleepiness
is present.
§ Intentionally not attending or responding to the task can make a person appear sleepy.
EEG, electroencephalogram; ESS, Epworth Sleepiness Scale; MSLT, multiple sleep latency test; MWT, maintenance of wakefulness test;
POMS, Profile of Mood States; SSS, Stanford Sleepiness Scale.
presence of sleepiness, the absence of sleepiness, or
changes in sleepiness. Is testing being conducted for clini-
cal assessment, research, or legal purposes? Is there self-
interest involved as part of a primary or secondary agenda?
With increasing frequency, sleep specialists are providing
expert opinions in legal matters involving accidents and
disability claims. Expert witnesses are often pressured to
render opinions concerning fitness for duty. In such cases,
objective testing is crucial. Furthermore, a normal test
result does not guarantee fitness for duty. Table 143-4
shows some characteristics of the tests described in this
chapter. Ideally, physiologic, manifest, and introspective
sleepiness should be assessed. In general, if a person claims
to be sleepy and the goal is to demonstrate sleepiness, the
MSLT is likely the best confirmatory test. If a person
claims not to be sleepy and the goal is to demonstrate an
ability to remain awake (as when there are concerns about
ability to operate a motor vehicle), the MWT has certain
advantages. 40 , 41
For clinical purposes, self-reported measures combined
with MSLT have long been the sine qua non for establish-
ing sleepiness. Sometimes, however, in cases involving
severe sleepiness, the MWT can demonstrate improved
alertness after treatment, whereas the MSLT shows little
or no change. Such persons continue to be pathologically
sleepy, but they are not overwhelmed by it during the brief
testing interval. The relationship between this pattern of
change and performance or behavior requires further
The dangers posed by excessive sleepiness are becoming
increasingly apparent. The National Commission on Sleep
Disorders Research catalogued a substantial list of sleep-
related industrial and transportation accidents. Long ago,
Kleitman proposed sleepiness as resulting from accumula-
tion of blood-borne hypnotoxins; however, such substances
have not been identified. Nonetheless, the search contin-
ues for sleep-inducing peptides (descendents of the hypoth-
esized hypnotoxins). Unfortunately, no convenient or
reliable blood test for sleepiness exists. Therefore, one or
a combination of the evaluation techniques described in
this chapter can be used and interpreted with respect to
the underlying physiologic drive for sleep, the subjective,
internalized consequence of that drive, and the behavioral
Clinical Pearl
Measuring sleepiness in a clinical setting is not a
simple matter. Testing for physiologic and manifest
sleepiness has become standardized in the MSLT and
MWT. The MSLT is indicated for evaluating narcolepsy
and idiopathic hypersomnia, and the MWT is indi-
cated for testing ability to remain awake when safety
is at stake. Sleepiness testing must always be viewed
within a larger context of a patient's clinical history
and examination findings.
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