Tests
1st tests to order
actigraphy and sleep diary
Test
It is recommended that the multiple sleep latency test be preceded by at least 1 week of actigraphic recording with a sleep log or diary to clarify if the results could be confounded by insufficient sleep, shift work, or another circadian sleep disorder.[1][90]
Result
no evidence of short sleep duration, no circadian disorder that could explain symptoms and/or lead to short sleep latency or sleep-onset rapid eye movement periods
overnight polysomnography
Test
May be normal (normal rapid eye movement [REM] sleep latency: 80 to 100 minutes); however, a short sleep latency (≤8 minutes) and one sleep-onset REM period is usually seen.[1][82]
Result
often shows snoring, frequent awakenings, reduced sleep efficiency, periods of REM sleep within the first 15 minutes of sleep, and multiple arousals
multiple sleep latency test (MSLT)
Test
An MSLT is performed only if the PSG performed the night before shows more than 6 hours of total sleep time.[82][84]
Rapid eye movement (REM) sleep-suppressing medications (such as antidepressants or stimulants) or withdrawal from these drugs can produce sleep-onset REM periods (SOREMPs) as a rebound phenomenon.
Medications that can affect REM sleep and/or nonrapid eye movement sleep latency should be tapered before the MSLT to minimize medication and substance effects, and the patient should be observed while off the agents for a sufficient time period before the test.[84]
During the MSLT, the patient is given 5 opportunities to nap, with trials starting every 2 hours.[84] A healthy subject falls asleep in about 10 to 15 minutes, whereas someone with narcolepsy often falls asleep in <8 minutes.[1][84][85]
The MSLT has false-negative results in 20% to 30% of patients and decreased sensitivity in older adult patients.[87] The MSLT is not appropriate for diagnosing narcolepsy in shift workers unless they have resumed a normal circadian pattern.[1]
Other sleep disorders (untreated sleep apnea, sleep deprivation, delayed sleep phase syndrome) as well as unaffected patients may also present with SOREMPs.[86][91]
Result
sleep latency ≤8 minutes plus ≥2 SOREMPs indicates narcolepsy
Tests to consider
HLA typing
Test
Most people with narcolepsy are HLA-DQB1*0602 positive, including those without cataplexy but with hypocretin deficiency (any patient who is HLA-negative is very likely to have normal hypocretin-1 levels).
Not specific for narcolepsy. Also found in 12% to 38% of the general population.[1]
Result
DQ0602 positive
cerebrospinal fluid hypocretin-1 level
Test
Deficiency is firmly established as a cause of narcolepsy type 1 and is a diagnostic marker.[1]
Indicated if MSLT results are uninterpretable or equivocal due to poor sleep efficiency (e.g., concurrent sleep disorders) or MSLT is not suitable (e.g., shift worker, or an inability to discontinue psychoactive drugs with REM sleep suppressive action).[88][89]
Result
low or undetectable in 90% of patients with cataplexy: levels of 110 picograms/mL or less than one third of mean values obtained in normal subjects with the same standardized assay are a diagnostic marker for narcolepsy type 1; patients with narcolepsy type 2 have normal levels of hypocretin-1
maintenance of wakefulness test
Test
May be indicated when the inability to remain awake constitutes a safety risk. The 40-minute protocol is the standard protocol used. The initial trial should begin 1.5-3.0 hours after termination of the preceding night’s sleep at home and a subsequent trial should begin 2 hours after the start of the prior trial.[82][84]
Result
positive if onset of sleep occurs within 40 minutes
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