Multiple Sleep Latency Test

The Multiple Sleep Latency Test (MSLT) is a standardized daytime diagnostic procedure that objectively measures an individual's sleep propensity by assessing how quickly they fall asleep and enter rapid eye movement (REM) sleep during a series of scheduled naps, typically conducted following an overnight polysomnography (PSG) to ensure adequate nighttime sleep.^[1] It serves as the primary tool for diagnosing sleep disorders characterized by excessive daytime sleepiness, such as narcolepsy and idiopathic hypersomnia.^[2][3] The MSLT is performed in a controlled sleep laboratory environment, where patients undergo five nap opportunities spaced approximately two hours apart, beginning 1.5 to 3 hours after the conclusion of the prior night's PSG, which must document at least six hours of sleep within a seven-hour time in bed.^[1] During each nap trial, the patient lies in a dark, quiet room and is instructed to attempt sleep while physiological signals—including electroencephalogram (EEG), electrooculogram (EOG), electromyogram (EMG), and electrocardiogram (EKG)—are recorded to monitor brain activity, eye movements, muscle tone, and heart rate; audiovisual surveillance ensures safety and compliance.^[2][4] Each trial concludes after 20 minutes if no sleep occurs or after 15 minutes of sustained sleep, with patients required to remain awake and avoid stimulating activities between naps.^[3] Preparation is critical, including a two-week sleep diary or actigraphy to establish baseline patterns, discontinuation of medications that influence sleep or REM (up to six weeks for long-acting drugs), and avoidance of caffeine or naps in the preceding days.^[1][4] Results are scored by calculating the mean sleep latency (MSL)—the average time from lights out to the first epoch of any sleep stage across the naps, capped at 20 minutes if no sleep occurs—and counting sleep-onset REM periods (SOREMPs), defined as REM sleep within 15 minutes of sleep onset.^[1] Interpretation by a board-certified sleep medicine physician integrates these metrics with the overnight PSG data; for instance, an MSL of ≤8 minutes with ≥2 SOREMPs supports a diagnosis of narcolepsy type 1, while an MSL ≤8 minutes without significant SOREMPs may indicate idiopathic hypersomnia.^[2][3] Normal MSL values typically exceed 10 minutes, with REM sleep rarely occurring in the first 90 minutes of sleep in healthy individuals.^[3] The test's protocols, established by the American Academy of Sleep Medicine (AASM), emphasize standardization to enhance reliability, though factors like medications or irregular sleep schedules can affect outcomes.^[1]

Overview

Definition and Purpose

The Multiple Sleep Latency Test (MSLT) is a standardized daytime polysomnographic assessment designed to objectively measure a person's tendency to fall asleep by evaluating sleep latency—the time required to transition from wakefulness to sleep—during multiple scheduled nap opportunities in a controlled, sleep-conducive environment.^[5] This test serves as the gold standard for quantifying physiological sleep propensity in the absence of external alerting factors, providing a validated metric of daytime sleepiness that complements subjective reports.^[5] The MSLT has evolved into a cornerstone procedure for evaluating hypersomnolence.^[5] The primary purpose of the MSLT is to diagnose and differentiate central disorders of hypersomnolence, such as narcolepsy type 1 and idiopathic hypersomnia, by quantifying excessive daytime sleepiness and detecting abnormal sleep-onset rapid eye movement periods (SOREMPs), which indicate disrupted sleep architecture.^[2][6] In clinical practice, it aids in confirming suspected narcolepsy when combined with other findings, such as cataplexy or hypocretin deficiency, and helps rule out other causes of sleepiness like insufficient sleep or sleep apnea.^[5] By providing objective data, the MSLT supports targeted treatment decisions, including pharmacological interventions for REM instability or behavioral modifications for hypersomnolence.^[6] Key components of the MSLT include five brief nap trials, typically spaced two hours apart and beginning 1.5 to 3 hours after the end of an overnight polysomnogram (PSG), ensuring the patient has achieved at least six hours of prior sleep to minimize confounding factors.^[2][5] The entire procedure spans approximately seven to eight hours, conducted in a dark, quiet laboratory setting to standardize conditions.^[6] Standardization of the MSLT follows rigorous guidelines from the American Academy of Sleep Medicine (AASM), which mandate polysomnographic monitoring via electroencephalography (EEG) for brain activity, electrooculography (EOG) for eye movements, electromyography (EMG) for muscle tone, and optionally electrocardiography (ECG) for cardiac rhythm, ensuring accurate staging of sleep onset and REM periods.^[5] These protocols, updated periodically based on evidence, require discontinuation of stimulants and REM-suppressing medications prior to testing to reflect true sleep propensity.^[5]

Clinical Indications

The Multiple Sleep Latency Test (MSLT) is primarily indicated for the diagnosis of narcolepsy, both with and without cataplexy, as well as idiopathic hypersomnia and other central disorders of hypersomnolence.^[5][1] In narcolepsy, the MSLT confirms excessive daytime sleepiness and the presence of sleep-onset REM periods when combined with clinical symptoms.^[5] For idiopathic hypersomnia, it helps differentiate the condition from narcolepsy by assessing persistent sleep propensity without REM abnormalities.^[1] The test is also used to evaluate treatment efficacy in these disorders, such as monitoring response to therapy in patients with diagnosed hypersomnolence.^[5] Referral for MSLT is recommended for patients presenting with unexplained excessive daytime sleepiness, typically indicated by an Epworth Sleepiness Scale score greater than 10, along with a history of sleep attacks or cataplexy.^[5][7] It is generally performed after ruling out insufficient sleep or obstructive sleep apnea through prior polysomnography (PSG).^[1] Contraindications include active untreated sleep apnea, shift work disorder without schedule adjustment, or conditions that prevent safe napping, such as severe cardiac issues like advanced congestive heart failure.^[5][8] The MSLT is not indicated for primary insomnia or circadian rhythm disorders.^[5] Recent 2024 refinements from the American Academy of Sleep Medicine (AASM) emphasize the MSLT's role in narcolepsy diagnosis only when preceded by an adequate PSG documenting at least 6 hours of sleep, to avoid misdiagnosis due to confounding factors like insufficient prior sleep.^[9] This aligns with studies highlighting the need for comprehensive evaluation to ensure accurate results.^[10]

Background

Historical Development

The Multiple Sleep Latency Test (MSLT) originated in the mid-1970s at Stanford University, where researchers William C. Dement and Mary A. Carskadon developed it as a standardized method to quantify daytime sleepiness. Building on earlier 1970s investigations into the effects of sleep deprivation, irregular sleep-wake schedules, and pharmacological interventions such as hypnotics, the test evolved from preliminary studies measuring sleep onset in controlled nap opportunities. Initial applications emerged around 1974, when Dement and colleagues used similar latency assessments to evaluate sleep disruption from jet lag and the efficacy of sedative-hypnotic drugs in modulating daytime alertness.^[11][12] The MSLT was formalized in 1977 through experiments involving repeated 90-minute sleep-wake cycles, which demonstrated its utility in capturing physiological sleep propensity across the day. A seminal 1978 publication by Carskadon and Dement introduced the test's protocol for distinguishing excessive daytime sleepiness in narcoleptic patients from healthy controls, establishing mean sleep latency as a key metric and highlighting sleep-onset REM periods (SOREMPs) as a diagnostic feature. By the 1980s, the MSLT became integral to narcolepsy diagnostics, with studies confirming its sensitivity in identifying pathological sleepiness and SOREMPs in clinical populations, paving the way for its routine use in sleep medicine.^[13][14] Early applications of the MSLT focused on healthy subjects to assess the impacts of environmental and pharmacological factors on sleep latency. Researchers employed it to quantify the soporific effects of alcohol, the alerting properties of stimulants like amphetamines, and the cumulative consequences of partial sleep loss, revealing dose-dependent reductions in latency that informed safety guidelines for shift workers and travelers. These foundational studies underscored the test's reliability in non-clinical contexts before its broader adoption in diagnosing hypersomnolence disorders.^[15][16] The MSLT's evolution continued with formal standardization by the American Sleep Disorders Association (ASDA; predecessor to the AASM), which adopted guidelines in 1992 specifying protocols for nap intervals, scoring, and indications to ensure reproducibility across labs. Subsequent refinements in 2005 incorporated updated diagnostic thresholds for mean sleep latency and SOREMPs in the International Classification of Sleep Disorders (ICSD-2), while 2012 AASM practice parameters emphasized integrating nocturnal polysomnography to mitigate confounds like sleep debt. Recent 2024 discussions highlight ongoing debates about the test's limitations when used in isolation, advocating for contextual clinical evaluation to improve diagnostic accuracy.^[17][9]

Physiological Basis

The physiological basis of the Multiple Sleep Latency Test (MSLT) centers on quantifying sleep propensity through the measurement of sleep latency, defined as the time from lights out to the onset of stage 1 sleep, which marks the transition from wakefulness to sleep. This latency reflects the dynamic interplay between the homeostatic sleep drive (Process S), which builds during wakefulness and dissipates during sleep, and circadian alertness (Process C), which modulates arousal according to the body's internal clock, as described in Borbély's two-process model of sleep regulation.^[18] In this framework, prolonged wakefulness intensifies Process S, lowering the threshold for sleep onset, while Process C promotes wakefulness during typical daytime hours; the MSLT captures this balance by assessing how quickly sleep occurs under standardized, quiet conditions that minimize external stimuli.^[19] Sleep-onset REM periods (SOREMPs), another key metric in the MSLT, occur when REM sleep begins within 15 minutes of sleep onset and signify instability in REM sleep regulation. In healthy individuals, REM sleep typically emerges after more than 90 minutes of sleep, following non-REM stages, but SOREMPs indicate a pathological intrusion of REM mechanisms into sleep initiation. This phenomenon is particularly linked to hypocretin (orexin) deficiency in narcolepsy type 1, where loss of hypocretin-producing neurons in the hypothalamus disrupts the normal suppression of REM sleep during wakefulness and early non-REM phases, leading to rapid transitions and fragmented sleep architecture.^[19] The MSLT employs polysomnographic monitoring to detect these processes, primarily through electroencephalography (EEG) to identify the alpha-to-theta rhythm transition signifying sleep onset, electrooculography (EOG) to capture rapid eye movements characteristic of REM sleep, and electromyography (EMG) to observe muscle atonia that confirms REM episodes.^[19] In hypersomnias such as narcolepsy and idiopathic hypersomnia, pathophysiology involves a reduced arousal threshold due to impaired wake-promoting systems, allowing sleep to onset more readily despite behavioral efforts to stay awake; the MSLT exploits this vulnerability by providing repeated opportunities for sleep in a controlled environment following nocturnal polysomnography, which establishes a baseline and rules out confounding factors like sleep-disordered breathing.^[19]

Preparation and Procedure

Patient Preparation

Proper preparation for the Multiple Sleep Latency Test (MSLT) is essential to ensure accurate assessment of daytime sleepiness by minimizing confounding factors that could influence sleep latency. This involves a prerequisite overnight polysomnography (PSG) study, adherence to specific behavioral guidelines, management of medications, and comprehensive patient education to promote compliance and reduce anxiety.^[1] The MSLT must follow an in-laboratory, attended PSG performed the night prior, which documents at least 6 hours of total sleep time to confirm adequate nocturnal sleep and rule out other sleep disorders such as obstructive sleep apnea that could confound results. The PSG should align with the patient's habitual major sleep period, avoiding split-night protocols or positive airway pressure titrations, and utilize the same electroencephalogram montage as the subsequent MSLT. The MSLT nap opportunities begin 1.5 to 3 hours after the end of the preceding overnight polysomnography (PSG) to allow for recovery while maintaining a controlled post-sleep environment.^[1][2] Patients receive detailed behavioral instructions to standardize conditions and avoid substances or activities that alter alertness. Patients should abstain from caffeine (ideally, with tapering if chronic use), alcohol, and other sedating or alerting substances on the day of the PSG and MSLT; nicotine use should cease at least 30 minutes before each nap, and any naps are prohibited to prevent interference with sleep propensity measurements. A regular sleep-wake schedule should be maintained for 1 to 2 weeks beforehand, ideally documented via a sleep diary and actigraphy to verify at least 6 to 7 hours of nightly sleep, with avoidance of insufficient sleep or prolonged daytime naps exceeding 1 hour. On the test day, vigorous exercise is prohibited throughout, and heavy meals should be avoided within 2 hours of each nap opportunity; instead, light meals such as breakfast at least 1 hour before the first nap and lunch after the second are recommended. A urine drug screen may be performed if nonadherence is suspected, and all medications and substances used within 24 hours should be documented.^[1][9][2] Medication management requires careful review by the clinician to eliminate or adjust drugs that affect sleep or wakefulness, with all current medications documented in the report for interpretive context. Stimulant medications, such as modafinil, should be discontinued at least 2 weeks prior to the test, extending to 6 weeks for agents with long half-lives to allow full clearance. Antidepressants and other REM-suppressing or alerting/sedating agents must be tapered and stopped 2 weeks in advance or based on 2 to 5 half-lives, whichever is longer, using clinical judgment to balance safety and diagnostic validity.^[1][9] Patient education is provided to set expectations and enhance cooperation, including explanations of the procedure's components to alleviate concerns. Individuals are informed that the MSLT consists of 4 to 5 scheduled nap attempts, each limited to 20 minutes in duration if sleep does not occur or terminated 15 minutes after sleep onset, conducted in a dark, quiet room with dim lighting to simulate soporific conditions. Post-nap assessments may include brief questionnaires on subjective sleepiness, similar to those in sleep diaries used pre-test, and patients are reassured about the application and removal of electrodes between trials for comfort. Addressing potential anxiety regarding the monitoring equipment and the need to lie still with eyes closed during attempts is emphasized to ensure relaxed participation.^[1][2]

Test Administration

The Multiple Sleep Latency Test (MSLT) is conducted in a controlled sleep laboratory environment, where the patient is fitted with a standardized polysomnographic electrode montage following the 10-20 international system. This includes at least three electroencephalogram (EEG) channels—frontal (F3-M2 or F4-M1), central (C3-M2 or C4-M1), and occipital (O1-M2 or O2-M1)—along with bilateral electrooculogram (EOG) leads for eye movements and submental electromyogram (EMG) for chin muscle activity; anterior tibialis EMG on both legs may be included to detect movements if clinically indicated, with an electrocardiogram (ECG) optionally included. The patient is positioned in a comfortable bedroom maintained in semi-darkness during naps, with continuous audiovisual monitoring via infrared video and audio recording to observe behavior and ensure protocol adherence.^[20] The MSLT schedule comprises four or five nap opportunities, with five naps as the recommended standard to enhance reliability, beginning 1.5 to 3 hours after the end of the preceding overnight polysomnography (PSG). Subsequent naps are scheduled at two-hour intervals from the start of the previous nap, typically spanning the morning and early afternoon (e.g., starting at 9:00 a.m., followed by 11:00 a.m., 1:00 p.m., 3:00 p.m., and optionally 5:00 p.m.). This timing assumes the patient obtained at least six hours of total sleep time during the prior PSG to minimize confounds from sleep deprivation.^[20] Each nap protocol begins with the technician instructing the patient to lie supine, assume a comfortable position, keep eyes closed, and attempt to fall asleep while remaining still and quiet. Lights are extinguished to create a dim, non-stimulating environment, with all electronic devices or alerting activities prohibited for at least 30 minutes beforehand; the patient must not leave the bed or engage in external stimuli. The nap terminates after 20 minutes if sleep does not occur or after 15 minutes of persistent sleep following onset (totaling 20 to 35 minutes), at which point lights are turned on to end the trial. Between naps, patients are required to stay awake, leave the bed, and participate in low-stimulation activities during breaks that accommodate light meals—such as breakfast one hour before the first nap and lunch after the second—with no napping permitted to preserve the test's validity.^[20] Data collection involves uninterrupted polysomnographic monitoring throughout all nap trials using the established electrode montage, capturing EEG, EOG, EMG, and ECG signals synchronized with time-stamped audiovisual recordings. A certified sleep technician oversees the recordings in real-time for quality control or scores sleep stages and events post hoc in accordance with American Academy of Sleep Medicine (AASM) guidelines, ensuring accurate documentation of sleep onset and architecture without interrupting the patient.^[20]

Interpretation

Measuring Sleep Latency

Sleep latency in the Multiple Sleep Latency Test (MSLT) is quantified as the duration from the initiation of each nap opportunity—marked by lights out—to the onset of sleep, defined as the beginning of the first 30-second epoch scored as any stage of sleep (N1, N2, N3, or REM) according to the American Academy of Sleep Medicine (AASM) Manual for the Scoring of Sleep and Associated Events.^[1] This scoring relies on polysomnographic recordings, including electroencephalography (EEG), electrooculography (EOG), and electromyography (EMG), to identify sleep stages based on characteristic waveforms and patterns.^[1] The mean sleep latency is then computed by averaging the individual latencies across all nap attempts, typically four to five naps conducted at two-hour intervals following an overnight polysomnogram (PSG).^[1] For nap opportunities where sleep does not occur within 20 minutes, the trial is terminated, and a default latency of 20 minutes is assigned to that nap for inclusion in the mean calculation, ensuring a standardized approach to averaging even incomplete attempts.^[1] If sleep is achieved, the nap continues for an additional 15 minutes after the first epoch of sleep to allow for further staging, but the latency measurement remains fixed at the time of initial sleep onset.^[1] Sleep-onset REM periods (SOREMPs) are measured by assessing the timing of REM sleep relative to sleep onset, specifically identifying instances where REM occurs within 15 minutes of the first sleep epoch during a nap.^[1] REM sleep is scored for a given epoch if it exhibits low-voltage, mixed-frequency EEG activity, intermittent rapid eye movements on EOG, and reduced or absent muscle tone on EMG, with at least one full 30-second epoch required to confirm the stage.^[1] The total number of SOREMPs is tallied across all naps, providing a key metric alongside sleep latency. Measurements in MSLT are influenced by variability factors such as the total sleep duration from the preceding PSG, with protocols mandating at least six hours of sleep to minimize confounds from sleep deprivation; insufficient prior sleep may elevate latencies and necessitate test repetition.^[1] Scoring is typically performed using specialized polysomnography software that automates epoch-by-epoch analysis, followed by manual verification by a registered polysomnographic technologist to ensure accuracy per AASM standards.^[1]

Diagnostic Criteria

The diagnostic criteria for disorders assessed via the Multiple Sleep Latency Test (MSLT) are outlined in the International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR), published by the American Academy of Sleep Medicine in 2023.^[21] These criteria integrate MSLT results—specifically mean sleep latency and sleep-onset REM periods (SOREMPs)—with clinical history, polysomnography (PSG) findings, and other objective measures to confirm central disorders of hypersomnolence, while requiring exclusion of alternative explanations such as insufficient sleep or comorbidities.^[21] PSG performed the night prior to MSLT must demonstrate adequate sleep duration for age (typically ≥6 hours) and rule out other primary sleep disorders like obstructive sleep apnea.^[1] For narcolepsy type 1, the ICSD-3-TR requires excessive daytime sleepiness (EDS) for ≥3 months and one or both of the following: (1) cataplexy with either mean sleep latency ≤8 minutes and ≥2 SOREMPs on MSLT or a sleep-onset REM period on the nocturnal PSG; or (2) cerebrospinal fluid (CSF) hypocretin-1 levels ≤110 pg/mL (or <1/3 of mean normal value using the same assay). Low CSF hypocretin-1 levels can support the diagnosis of narcolepsy type 1 even in the absence of cataplexy.^[21] These features must not be better explained by another sleep, medical, or neurologic disorder.^[21] Narcolepsy type 2 diagnosis per ICSD-3-TR necessitates EDS for ≥3 months, mean sleep latency ≤8 minutes and ≥2 SOREMPs on MSLT, in the absence of cataplexy and with normal CSF hypocretin-1 levels (or untested).^[21] Symptoms must persist despite adequate sleep hygiene and cannot be attributable to other conditions.^[21] Idiopathic hypersomnia criteria under ICSD-3-TR include daily periods of irrepressible need to sleep or daytime lapses into sleep for ≥3 months, with at least one of: (1) excessive sleepiness despite normal sleep time (≥6.5 hours) confirmed by history, sleep log, actigraphy, or total 24-hour sleep time ≥660 minutes confirmed by PSG and MSLT after correcting sleep deprivation; or (2) long unrefreshing naps (>10 hours). PSG and MSLT findings must not be consistent with narcolepsy type 1 or 2 (e.g., fewer than 2 SOREMPs if MSLT is performed). There is no cataplexy, and other causes of hypersomnolence are excluded. Supporting features include sleep inertia and high sleep efficiency (≥90%) on PSG.^[21][22] MSLT reports typically include the mean sleep latency across naps, the number of SOREMPs, and overall sleep efficiency, which are interpreted alongside clinical history, Epworth Sleepiness Scale scores, and PSG data for comprehensive diagnosis.^[1] Recent critiques, including those from 2023 and 2024 analyses, highlight the ICSD-3-TR's potential over-reliance on MSLT, which exhibits poor test-retest reliability (e.g., only 25% consistency on repeat testing for hypersomnolence disorders) and may miss comorbidities such as mood disorders or residual sleep apnea effects that confound results.^[23] Up to 40% of idiopathic hypersomnia cases show normal MSLT findings, potentially leading to underdiagnosis, while the test's 8-minute threshold lacks validation across diverse populations.^[24] These limitations underscore the need for integrated clinical evaluation beyond MSLT alone.^[25]

Limitations and Alternatives

Common Limitations

The Multiple Sleep Latency Test (MSLT) exhibits significant subjectivity and variability, as results can be influenced by patient motivation, anxiety, or subtle prior sleep deprivation, leading to inconsistent sleep onset measurements. For example, even mild accumulated sleep debt can shorten mean sleep latency and induce sleep-onset REM periods (SOREMPs), resulting in false-positive diagnoses of narcolepsy. In patients with depression, the MSLT performs poorly as an objective measure of sleepiness due to the complex interplay between hypersomnolence and psychiatric symptoms, often yielding unreliable quantifications. Similarly, untreated or inadequately assessed obstructive sleep apnea during the preceding polysomnography (PSG) can produce false positives by mimicking narcoleptic features on the MSLT. The MSLT demonstrates limited sensitivity and specificity, particularly for atypical forms of narcolepsy such as type 2 (NT2), where 2023-2024 studies indicate frequent missed diagnoses due to inconsistent SOREMP detection and variable sleep latency thresholds. Overall sensitivity for narcolepsy type 1 (NT1) ranges from 80% to 95% with specificity up to 98%, but these metrics drop substantially for NT2 and idiopathic hypersomnia, with test-retest instability affecting over 50% of cases in non-cataplectic hypersomnias. The test is less suitable for children and the elderly owing to age-specific normative differences; pediatric MSLT results are borderline in about 21% of cases, potentially missing narcolepsy or hypersomnia under adult criteria, while in older adults, mean sleep latency progressively increases and SOREMP frequency decreases, reducing diagnostic yield. Practical constraints further limit the MSLT's utility, as it is costly—typically $600 to $2,200 when bundled with overnight PSG—and time-intensive, requiring a full nocturnal recording followed by four to five daytime naps spanning more than 10 hours in a controlled laboratory setting. Accessibility is restricted by its dependence on specialized sleep centers, and reproducibility remains poor, with diagnostic classifications changing in 20% to 50% of repeat tests, especially for NT2 and idiopathic hypersomnia. As an alternative, simpler objective measures like the Maintenance of Wakefulness Test may be considered in select cases to assess alertness without the same overnight commitment. Artifacts pose additional challenges to MSLT reliability, including electrode detachment, patient movement during naps, or environmental noise, which can distort electroencephalographic signals and lead to invalid sleep latency readings. Conditions like severe anxiety or claustrophobia may exacerbate movement artifacts or prevent completion, though these are not absolute contraindications.

Related Tests

The Maintenance of Wakefulness Test (MWT) complements the MSLT by assessing an individual's ability to resist sleep under conditions conducive to drowsiness, rather than measuring the propensity to fall asleep.^[26] It typically involves four 40-minute sessions where the patient sits quietly in a dimly lit room, with sleep latency exceeding 40 minutes considered normal and indicative of sufficient alertness, particularly for occupational evaluations such as in pilots or drivers.^[27] Unlike the MSLT, which evaluates physiologic sleepiness, the MWT targets manifest sleepiness and can help differentiate conditions where sustained wakefulness is critical.^[28] Actigraphy serves as a non-invasive alternative for monitoring sleep-wake patterns over extended periods, such as days or weeks, using wearable devices that detect movement to infer rest-activity cycles.^[29] It is particularly useful for evaluating circadian rhythm disorders or chronic insomnia but provides less detailed physiological data compared to polysomnography (PSG), lacking direct measures of brain activity or sleep stages.^[30] Actigraphy is often employed prior to MSLT or PSG to ensure adequate sleep duration leading up to testing, offering a practical screening tool for long-term patterns without laboratory constraints.^[31] The Epworth Sleepiness Scale (ESS) is a subjective screening questionnaire that quantifies daytime sleepiness through self-reported likelihood of dozing in eight common situations, with scores greater than 10 suggesting excessive sleepiness that may warrant objective testing like the MSLT.^[32] While quick and easy to administer, the ESS is not diagnostic on its own, as it relies on patient perception and correlates variably with objective measures, serving primarily as an initial filter for hypersomnia evaluation.^[33] The MSLT is routinely integrated with overnight PSG to rule out other sleep disorders and establish baseline sleep architecture before daytime testing.^[34] For narcolepsy confirmation, alternatives include cerebrospinal fluid measurement of orexin (hypocretin) levels, where values below 110 pg/mL indicate deficiency in over 90% of type 1 cases, or genetic testing for the HLA-DQB1*06:02 allele, present in nearly all hypocretin-deficient patients.^[35] These biomarkers provide targeted diagnostic support when MSLT results are ambiguous, particularly in confirming central hypersomnias.^[36] Emerging approaches include pilot studies on home-based MSLT variants and wearable EEG devices for ambulatory sleep latency assessment, leveraging post-2020 advancements in remote neurophysiology to enhance accessibility, though these remain unstandardized and require validation against lab protocols.^[37]