What are the differences in protocol between the Maintenance of Wakefulness Test (MWT) and the Multiple Sleep Latency Test (MSLT)?

Protocol Differences Between MWT and MSLT

The Maintenance of Wakefulness Test (MWT) measures your ability to stay awake in a quiet, dimly lit environment, while the Multiple Sleep Latency Test (MSLT) measures how quickly you fall asleep under similar conditions—they assess fundamentally different abilities (alertness versus sleepiness propensity) and are only weakly correlated with each other. 1

Core Conceptual Difference

The MWT and MSLT measure distinct physiological capacities that account for less than 17% of shared variability between tests 1:

• MSLT: Quantifies the propensity to fall asleep during the main waking period—essentially measuring sleepiness 2, 3
• MWT: Quantifies the ability to remain awake during soporific circumstances—measuring alertness or wake tendency 2, 3, 4

Patients can be discordant on these tests: some with abnormally low MSLT scores (high sleepiness) can still stay awake when instructed on the MWT, while others who fail the MWT may not fall asleep quickly on the MSLT 1

Protocol Specifications

Test Duration and Timing

MSLT Protocol 2, 3:

• Performed during the main period of wakefulness
• Consists of 4-5 nap opportunities
• Each trial allows up to 20 minutes for sleep onset
• Trials separated by 2-hour intervals
• Must be performed the day after nocturnal polysomnography 3

MWT Protocol 3, 4:

• Standard protocol uses 40-minute trials (though 20-minute protocol exists)
• Consists of 4 trials
• Trials separated by 2-hour intervals
• Performed in much the same timing structure as MSLT 3

Environmental Conditions

MSLT 2:

• Standardized laboratory conditions designed to facilitate sleep
• Patient lies in bed
• Dark, quiet environment

MWT 4:

• Soporific but wake-promoting circumstances
• Patient sits upright in bed or chair with back and head supported
• Dim lighting (specific illuminance level standardized)
• Controlled room temperature
• Patient instructed to remain awake and resist sleep 4

Patient Instructions

MSLT 2, 3:

• Patient instructed to try to fall asleep
• Measures passive sleep tendency

MWT 3, 4:

• Patient instructed to avoid moving voluntarily and to stay awake
• Measures active resistance to sleep
• Tests volitional ability to maintain wakefulness

Pre-Test Preparation Requirements

Both tests share critical preparation requirements 5, 6, 7:

• Actigraphy monitoring: 7-14 days prior to testing to document adequate sleep time and habitual sleep-wake patterns 5, 7
• Medication discontinuation: Stimulants (amphetamines, methylphenidate, modafinil) and sedating medications (benzodiazepines, hypnotics, antihistamines) must be stopped before testing 6
• Urinary drug screening: Should be performed to detect undisclosed drug use that could invalidate results 8
• Overnight polysomnography: Required the night before MSLT to ensure adequate sleep 3

Clinical Indications

MSLT is indicated for 5, 2:

• Diagnosis of narcolepsy (mean sleep latency ≤8 minutes with ≥2 sleep-onset REM periods) 2, 3
• Differentiating narcolepsy from idiopathic hypersomnia 2
• NOT routinely indicated for OSA diagnosis or CPAP treatment assessment 5

MWT is indicated for 5, 2:

• Assessing response to treatment in patients with excessive sleepiness 5, 2
• Evaluating individuals in safety-sensitive positions where inability to remain awake constitutes a safety issue 5, 2, 3
• Assessing commercial motor vehicle operators with treated OSA 5

Normative Values and Interpretation

MSLT 2:

• Mean sleep latency <5 minutes: observed in majority of narcolepsy patients
• Mean sleep latency ≤8 minutes with ≥2 SOREMPs: diagnostic for narcolepsy

MWT (40-minute protocol) 4:

• Normal mean sleep latency: 35.2 ± 7.9 minutes
• Lower normal limit: 19.4 minutes (two standard deviations below mean)
• Values significantly higher than those in patients with excessive somnolence disorders

Critical Pitfalls

• Do not use tests interchangeably: They measure different constructs and cannot substitute for each other 1
• MWT limitations in safety assessment: Despite use in transportation workers, there is little evidence linking MWT scores with actual accident risk in real-world circumstances 5, 3
• Subjective measures unreliable in employment settings: Transportation workers may underreport sleepiness when job security is at stake, making objective testing essential but not solely determinative 5
• Inadequate sleep before MSLT: Will produce false-positive results; actigraphy documentation is essential to avoid misdiagnosis 5, 7
• Undisclosed drug use: 16% of patients test positive for drugs not self-reported, which can invalidate results 8