Sleep Disorders: Clinical Review of Diagnosis, Mechanisms, and Emerging Pharmacotherapies Aligned with ICSD-3-TR

Abstract

Background Sleep is a core biomarker of physical and mental health, influencing multisystem function and quality of life, and insufficient sleep duration or fragmentation is associated with increased risk of hypertension and cardiometabolic disease as well as impaired cognition and emotional well-being.[1] High-burden clinical entities span insomnia disorder, obstructive sleep apnea (OSA), central disorders of hypersomnolence (notably narcolepsy), circadian rhythm sleep–wake disorders, parasomnias such as REM sleep behavior disorder (RBD), and sleep-related movement disorders such as restless legs syndrome (RLS).[2–7]

Methods and scope This review synthesizes clinically actionable, citable findings from recent guideline-adjacent reviews and randomized trial data spanning symptom definitions, diagnostic workups (questionnaires, polysomnography, home testing, circadian biomarkers), mechanisms (hyperarousal and orexin signaling, OSA endotypes, hypocretin deficiency, circadian pacemaker biology, REM atonia circuitry, brain iron and dopaminergic/glutamatergic pathways), and evidence-based interventions including behavioral therapies, device therapies, and emerging pharmacotherapies (dual orexin receptor antagonists; incretin-based therapy for obesity-associated OSA; wake-promoting agents; IV iron and α2δ ligands).[4, 7–16]

Key findings Chronic insomnia disorder affects an estimated 6–15% of adults worldwide and is frequently underrecognized in routine care.[17, 18] OSA affects approximately one billion people and, when untreated, is linked to a two- to threefold higher risk of stroke and all-cause mortality.[3, 10] In obesity-associated moderate-to-severe OSA, tirzepatide reduced the apnea–hypopnea index (AHI) by −25.3 and −29.3 events/hour at 52 weeks in two phase 3 trials and achieved stringent combined response criteria in up to 50.2% of participants.[19] Narcolepsy type 1 is characterized by cataplexy and markedly reduced cerebrospinal fluid (CSF) hypocretin-1 (<110 pg/mL), with diagnosis anchored by overnight polysomnography followed by a Multiple Sleep Latency Test (MSLT) showing mean sleep latency <8 minutes and ≥2 sleep-onset REM periods (SOREMPs).[11, 20] iRBD is a high-risk prodromal synucleinopathy state, with meta-analytic phenoconversion rates of 33%, 82%, and 97% at 5, 10.5, and 14 years.[21]

Conclusions Contemporary sleep-medicine practice increasingly requires phenotype-precise diagnosis (including endotype-informed OSA management and biomarker-anchored circadian assessment) and risk-stratified treatment selection that integrates behavioral, device, and pharmacologic approaches while explicitly addressing comorbidity (mood disorders, cardiometabolic disease, chronic pain, neurodegeneration).[10, 12, 18, 22–24]

1. Introduction and Classification Framework

Sleep disturbance has progressed from a symptomatic epiphenomenon to a routinely interpretable clinical signal because sleep is a key biomarker of physical and mental health and because insufficient sleep duration and fragmentation are associated with downstream cardiometabolic and neurobehavioral risk.[1] Within ICSD-3–derived nosology, circadian rhythm sleep–wake disorders are explicitly classified as endogenous (e.g., delayed sleep–wake phase disorder, advanced sleep–wake phase disorder, non-24-hour sleep–wake rhythm disorder, irregular sleep–wake rhythm disorder) or exogenous (shift work, jet lag).[5] Other major syndromes emphasized in contemporary practice include insomnia disorder (defined by sleep-initiation or sleep-maintenance difficulty with daytime manifestations), obstructive sleep apnea (repetitive upper-airway collapse with intermittent hypoxia and fragmented sleep), narcolepsy (central hypersomnolence with REM dissociation), REM sleep behavior disorder (loss of REM atonia with dream enactment), and restless legs syndrome (sensorimotor urge to move with circadian worsening).[2–4, 6, 15]

Across these disorders, modern sleep medicine increasingly relies on

1. explicit operational diagnostic thresholds (e.g., insomnia frequency/duration; MSLT cutoffs; AHI event definitions),
2. careful selection among objective tools (laboratory polysomnography vs home sleep apnea testing vs actigraphy and emerging wearable EEG), and
3. mechanistically aligned therapeutics that target the proximate pathophysiology (orexin hyperarousal in insomnia; pharyngeal collapsibility and ventilatory-control traits in OSA; hypocretin deficiency in narcolepsy; REM atonia circuitry failure in RBD; brain iron deficiency and dysregulated neurotransmission in RLS).[2, 4, 8–10, 14, 20]

2. Insomnia Disorder

Insomnia is defined as difficulty in sleep induction or maintenance accompanied by daytime manifestations and is frequently described as the most prevalent sleep disorder.[2] Approximately 30% to 50% of adults report short-term insomnia symptoms, while up to 10% meet criteria for chronic insomnia, with higher prevalence in older individuals.[2] Chronic insomnia disorder is also summarized as affecting 6–15% of adults globally, indicating substantial population burden even when applying stricter diagnostic criteria.[17]

Definition and epidemiology

ICSD-3 and DSM-5 operationalize chronic insomnia diagnosis by requiring symptoms to occur at least three times per week and persist for at least three months.[8] In primary care, insomnia is highly prevalent and commonly comorbid with medical and psychiatric illnesses yet remains underdiagnosed and undertreated.[18] Consistent with this under-recognition, 70% of respondents in a National Sleep Foundation survey reported that clinicians never asked them about their sleep.[18] Across international studies, insomnia prevalence is often reported in the 10–30% range in the general population, reflecting differences in definitions and ascertainment and reinforcing the need for consistent operational thresholds in routine practice and research.[8, 25]

Pathophysiology

Insomnia is increasingly conceptualized as a disorder of hyperarousal, in which patients demonstrate central and autonomic nervous system hyperactivation.[9] Hyperarousal is described as heightened cortical activity with increased metabolic rate, elevated heart rate, and increased sympathetic tone.[9] Chronic stress can reinforce insomnia via hypothalamic–pituitary–adrenal (HPA) axis activation with increased corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol, perpetuating insomnia and hyperarousal in a self-reinforcing cycle.[9] The progression from acute to chronic insomnia is framed by the 3P model, in which predisposing, precipitating, and perpetuating factors act on brain centers that govern the emergence and persistence of insomnia.[8]

Orexin (hypocretin) signaling provides a mechanistically coherent bridge between hyperarousal physiology and pharmacologic targeting, because orexin promotes wakefulness through two G-protein–coupled receptors (OX1R and OX2R).[2] Hypothalamic orexin neurons coordinate sleep–wake transitions and integrate metabolic, emotional, and circadian signals, and disruption or hyperactivity of this system is cited as a strong contributor to chronic insomnia through increased arousal and difficulty initiating sleep.[9]

Diagnostic criteria and workup

Clinical assessment is anchored in structured history consistent with ICD-11–aligned questioning: the nature of the sleep disturbance (delayed sleep onset, trouble staying asleep, early morning awakening, nonrestorative sleep), sleep routines and maladaptive habits, daytime impairment, and the presence of contributing comorbidities.[18] When needed, additional screening tools and laboratory or sleep studies are used to rule out other conditions that disrupt sleep, including mood disorders, pain, restless legs syndrome, and obstructive sleep apnea.[18]

Severity monitoring can be quantified with the Insomnia Severity Index (ISI), a 7-item patient self-reported questionnaire that assesses nighttime and daytime aspects of sleep disturbance, with results classifying insomnia as not present, mild, moderate, or severe.[18] Polysomnography is not usually necessary and is not recommended for the initial objective assessment of insomnia, emphasizing that insomnia is most often a clinical diagnosis supplemented by targeted testing when another disorder is suspected.[18]

Evidence-based treatment

Major sleep guidelines (including the American Academy of Sleep Medicine, the American College of Physicians, and the European Sleep Research Society) strongly recommend cognitive behavioral therapy for insomnia (CBT-I) as first-line treatment.[18] Evidence summarized in clinical reviews indicates that CBT-I alone offers greater long-term efficacy than insomnia medications with few adverse effects, while noting that trials directly comparing CBT-I with dual orexin receptor antagonists (DORAs) are not yet available in the cited source base.[18]

Pharmacotherapy is most defensible when insomnia persists despite CBT-I availability or when targeted short-term symptom control is required, with increasing emphasis on orexin-pathway therapies that modulate wake promotion rather than intensifying GABAergic sedation.[18, 26] DORAs block both OX1R and OX2R to reduce wakefulness and promote sleep and are described as facilitating sleep initiation and maintenance without significantly disrupting overall neurophysiological balance.[9, 22]

A network meta-analysis of eight double-blind randomized placebo-controlled trials (5198 adults; mean age 56.33 years; 67.84% female) compared daridorexant (25 mg/day, 50 mg/day), lemborexant (5 mg/day, 10 mg/day), and suvorexant (20 mg/day; 15 mg/day for people ≥65 years) and found that all active treatments outperformed placebo for efficacy outcomes including subjective time to sleep onset and subjective total sleep time at month 1.[27] In that analysis, somnolence occurred more frequently with several DORA regimens versus placebo, with lemborexant 10 mg linked to higher discontinuation due to adverse events than suvorexant 20/15 mg and a higher incidence of somnolence than multiple comparators.[27] Mechanistically and clinically, DORAs are described in this meta-analysis as not associated with physiological tolerance, withdrawal, or rebound insomnia upon abrupt discontinuation and not associated with deleterious effects on sleep architecture.[27]

Dose-specific daridorexant trial data show clinically meaningful objective improvements in wake after sleep onset (WASO), with WASO reduced in a dose-dependent manner by 28.4, 32.3, 37.7, and 47.1 minutes across 5, 10, 25, and 50 mg groups over days 1–2 (p<0.001).[28] In the same cited trial source, at least one adverse event occurred in 35%, 38%, 38%, 34%, 30%, and 40% of patients receiving daridorexant 5, 10, 25, 50 mg, placebo, and zolpidem, respectively.[28] The recommended daily dose is 50 mg once daily within 30 minutes before bedtime when at least 7 hours remain for sleep, with dose reduction to 25 mg in moderate hepatic impairment and avoidance in severe hepatic impairment.[28]

A post hoc analysis of a phase 3 randomized double-blind placebo-controlled trial subgroup with comorbid insomnia disorder and untreated mild OSA (AHI 5–<15 events/h) found that daridorexant 50 mg improved PSG-measured WASO from baseline by −37.7 minutes at month 1 and −35.4 minutes at month 3, with significant placebo-corrected differences at both time points (−24.0 minutes at month 1, p=0.0009; −19.8 minutes at month 3, p=0.0203).[29] In that subgroup, daridorexant 50 mg also improved latency to persistent sleep (LPS) by −31.0 minutes at month 1 and −36.9 minutes at month 3, with a significant placebo-corrected difference at month 3 (−18.9 minutes, p=0.0039).[29] Safety findings in that subgroup included adverse events in 41.5% (daridorexant 50 mg), 28.2% (daridorexant 25 mg), and 31.9% (placebo), with somnolence and headache among the most common events and no discontinuations due to adverse events in the daridorexant arms.[29]

The following table summarizes selected insomnia interventions and key evidence points supported by the cited source base.

Latest advances and controversies

European guideline commentary summarized in real-world experience reports states that the introduction of DORAs has been the most significant recent pharmacologic development in insomnia, while also noting that data remain to be validated through everyday practice experience.[17] Comparative synthesis emphasizes that dosing influences sleep maintenance, with higher DORA doses correlating with longer total sleep time within individual drugs in pooled analyses.[2] Evidence limitations remain prominent, including the absence of direct head-to-head comparisons across different DORAs and the restriction of many studies to adult insomnia cohorts excluding important comorbidities, which constrains generalizability to complex clinical populations such as those with cardiopulmonary disease or neurodegeneration.[2] Subjective patient-reported sleep outcomes can be variable and uncertain, requiring careful interpretation and alignment with objective measures where available.[2]

Early-phase orexin-modulating agents continue to emerge, exemplified by TS-142, a novel DORA designed for fast absorption and short plasma half-life, though high screen-failure rates and small completion numbers have limited generalizability in the cited study context.[30]

Comorbidity and consequences

Chronic insomnia is associated with substantial daytime impairment, including tiredness, impaired concentration, and mood changes, and is linked in mechanistic framing to increased incidence of heart disease, diabetes, depression, anxiety, and weakened immune function.[9] Insomnia is strongly interwoven with depressive disorders: over 80% of individuals with major depressive disorder report significant sleep disturbance, insomnia can precede depressive episodes and predict both initial development and recurrence of depression, and persistent sleep disturbance after remission correlates with relapse risk and reduced therapeutic responsiveness.[22]

3. Sleep-Related Breathing Disorders

OSA is characterized by repetitive episodes of complete or partial collapse of the upper airway during sleep, producing intermittent hypoxia and fragmented sleep.[3] The estimated global burden is substantial: OSA is estimated to affect one billion people, and obstructive sleep apnea syndrome is described as affecting 936 million adults worldwide including 425 million with moderate-to-severe disease.[3, 10] Prevalence increases in men, older adults, and individuals with obesity.[3] Untreated obstructive sleep apnea syndrome is linked to a two- to threefold higher risk of stroke and all-cause mortality in long-term cohort studies.[10]

Pathophysiology

OSA pathophysiology involves both anatomical and functional contributors leading to upper-airway collapse during sleep.[3] Anatomical risk factors include a narrow or collapsible airway, enlarged tonsils, a large tongue, and craniofacial abnormalities such as retrognathia or maxillary hypoplasia that reduce airway patency.[3] Functional factors include reduced neuromuscular control of airway muscles, low arousal threshold, and high loop gain, producing ventilatory instability.[3] Contemporary conceptual models emphasize four modifiable traits—pharyngeal collapsibility, neuromuscular compensation, loop gain, and arousal threshold—that explain clinical heterogeneity and predict response to treatments (e.g., dominant anatomical collapse responding better to mechanical splints, surgery, or hypoglossal nerve stimulation; high loop gain responding to respiratory-stabilizing strategies).[10]

Repetitive obstruction generates cycles of hypoxia and reoxygenation that contribute to oxidative stress and systemic inflammation, and the resulting sleep fragmentation and intermittent hypoxia have multisystem effects increasing risk for cardiovascular, metabolic, and neurocognitive impairments.[3] Obesity worsens OSA via fat accumulation around the upper airway that narrows the lumen and increases collapsibility, reduced muscle tone particularly during REM sleep, and chronic low-grade systemic inflammation affecting upper-airway tissues.[31]

Diagnostic criteria and workup

Case-finding can be supported by screening tools such as STOP-Bang, which has high sensitivity for moderate-to-severe OSA but limited specificity that necessitates confirmatory testing.[10] The NoSAS score provides a more recent screening alternative with comparable diagnostic accuracy and fewer items.[10]

Full overnight polysomnography (PSG) remains the diagnostic gold standard because it enables comprehensive evaluation of sleep stages, arousals, respiratory events, and comorbid sleep disorders.[10] Home sleep apnea testing has gained acceptance for uncomplicated adults with suspected moderate-to-severe OSA to improve access, but it is less sensitive in mild OSA and may underestimate severity due to the absence of electroencephalographic sleep staging.[10] Event-definition details matter in clinical trials and can influence generalizability: in a recent major OSA pharmacotherapy trial program, hypopneas were scored centrally using an American Academy of Sleep Medicine rule specifying ≥30% airflow reduction for ≥10 seconds with ≥4% oxygen desaturation.[19] Diagnostic innovations such as wearables can improve accessibility but are limited by variability in sleep apnea definitions across studies and limited accuracy of some devices in measuring all sleep stages.[32]

Evidence-based treatment

Continuous positive airway pressure (CPAP) remains the cornerstone and gold-standard therapy for OSA.[3, 10] Large randomized trials and meta-analyses confirm CPAP effectiveness in normalizing AHI, improving daytime sleepiness, and reducing blood pressure, though cardiovascular hard-outcome protection has been inconsistent across some trials.[10] Individual patient data meta-analyses indicate that cardiovascular benefit is strongly adherence-dependent, with protective effects observed in patients using CPAP for more than 4 hours per night.[10] Adherence remains a major barrier because discomfort, noise, and mask inconvenience contribute to difficulty sustaining therapy.[3]

Alternative and adjunctive therapies are increasingly selected by phenotype and patient preference. Mandibular advancement devices are the most widely studied alternative and improve daytime sleepiness and quality of life in mild-to-moderate OSA, though they generally produce smaller AHI reductions than CPAP.[10] Positional OSA—events predominantly in the supine position—affects up to one-third of patients, and positional interventions can reduce AHI, but long-term adherence frequently limits sustained benefit.[10] Hypoglossal nerve stimulation has emerged as a therapy for PAP-intolerant patients with moderate-to-severe OSA who lack complete concentric palatal collapse, though surgical invasiveness, high cost, and restricted eligibility limit widespread use.[10] Surgical options show variable durability: uvulopalatopharyngoplasty has variable efficacy with relapse, whereas maxillomandibular advancement demonstrates the highest success rates with meta-analytic confirmation of long-term improvements in AHI and oxygenation, particularly in patients with craniofacial risk factors.[10]

Pharmacotherapy in OSA has historically focused on residual symptoms rather than airway obstruction. Solriamfetol and pitolisant are approved for residual excessive daytime sleepiness despite PAP, improving functional outcomes without reducing AHI.[10] In a one-year study context, pitolisant reduced Epworth Sleepiness Scale (ESS) scores from baseline with pooled mean difference −8.0 (95% CI −8.3 to −7.5), with no cardiovascular safety issues reported in the cited analysis.[33]

A major 2024-era shift toward disease modification in obesity-associated OSA is incretin-based therapy. Liraglutide reduced AHI by −12.2 events/hour versus −6.1 events/hour with placebo in one trial summary, supporting a precedent for weight-loss pharmacotherapy to reduce OSA burden.[3] The phase 3 SURMOUNT-OSA trials established tirzepatide as a high-efficacy option in moderate-to-severe OSA with obesity: at week 52, mean AHI change was −25.3 events/hour with tirzepatide versus −5.3 with placebo in trial 1 and −29.3 versus −5.5 in trial 2 (both P<0.001).[19] Up to 50.2% of tirzepatide-treated participants met a combined key secondary endpoint of fewer than 5 AHI events/hour or 5–14 events/hour with ESS ≤10, a threshold set that the trial authors note is relevant to clinical decisions about whether PAP therapy may be recommended.[19] Trial conclusions also describe improvements in body weight, hypoxic burden, hsCRP, systolic blood pressure, and sleep-related patient-reported outcomes in the tirzepatide group compared with placebo.[19] Adverse events were common in both arms but were generally gastrointestinal and more frequent with tirzepatide (79.8–83.2% vs 72.8–76.7% across trials), with overall serious adverse events reported in 7.5% and two adjudicated cases of acute pancreatitis in trial 2; no medullary thyroid cancer was reported in the cited text.[19]

Regulatory and mechanistic considerations increasingly intersect in obesity-associated OSA: one review source states that in June 2024 the FDA officially approved tirzepatide for obesity-associated obstructive sleep apnea syndrome, describing it as the first GLP-1–based therapy to receive this indication in that framing.[34] Mechanistically, uncertainty persists regarding the specific pathways by which GLP-1 signaling influences respiratory control and upper-airway muscle tone, and long-term efficacy and safety data in OSA populations remain limited in the cited reviews.[3]

Latest advances and controversies

Implementation science is increasingly central in OSA because telemonitoring of CPAP adherence can provide real-time feedback and improve long-term usage, and virtual care pathways integrating screening questionnaires, HSAT, remote initiation, and digital adherence support are increasingly feasible for expanding access.[10] However, controversies persist regarding:

• (i) inconsistent cardiovascular outcome signals of CPAP partly explained by adherence heterogeneity,
• (ii) underestimation of disease severity with HSAT, oximetry, and wearables compared with PSG, particularly in mild disease or comorbidity contexts, and
• (iii) trial-design limitations for pharmacotherapies such as insufficient duration to assess long-term cardiovascular outcomes and uncertain minimal clinically important thresholds for some patient-reported outcome measures in trial settings.[10, 19]

Central Disorders of Hypersomnolence

Narcolepsy is a rare but disabling neurological disorder involving disruption of the sleep–wake cycle and remains under- or misdiagnosed in many settings.[4] ICSD-3 classifies narcolepsy primarily into type 1 (NT1) and type 2 (NT2).[11] The onset commonly occurs in adolescence or early adulthood, while diagnosis is often delayed by 8–12 years, reinforcing the need for structured evaluation of chronic excessive daytime sleepiness (EDS).[35]

Pathophysiology

NT1 is primarily associated with loss of hypocretin (orexin) neurons with autoimmune and genetic risk factors, and loss of hypocretin neurons leads to reduced and inconsistent firing of wake-promoting neurons with unstable transitions between wakefulness and sleep.[4, 20] NT1 is characterized by cataplexy and significantly reduced orexin levels in CSF, with a cited threshold of <110 pg/mL for CSF hypocretin-1.[11] Genetic susceptibility includes the HLA-DQB1*06:02 allele, and environmental triggers linked to increased incidence include H1N1 influenza infection or vaccination, including increased incidence observed in children and adolescents infected with H1N1 or receiving the Pandemrix vaccine.[11, 20] Cataplexy is mechanistically conceptualized as intrusion of REM atonia circuitry into wakefulness.[20]

Diagnostic criteria and workup

Persistent and severe EDS lasting longer than 3 months warrants thorough evaluation for narcolepsy.[20] Subjective assessment can use validated questionnaires such as the Epworth Sleepiness Scale and Stanford Sleepiness Scale.[20] Diagnostic confirmation involves overnight polysomnography to assess sleep architecture and exclude other sleep disorders contributing to EDS, followed by next-day MSLT.[20] Established diagnostic criteria confirm narcolepsy when mean sleep latency is less than 8 minutes and at least two SOREMPs occur across five nap opportunities.[20] MSLT sensitivity is approximately 85% in patients with cataplexy, highlighting both its central role and its limitations in certain phenotypes.[20]

CSF hypocretin-1 measurement provides a high-specificity biomarker complement in appropriate contexts: patients with narcolepsy accompanied by cataplexy typically demonstrate CSF hypocretin-1 ≤110 pg/mL or less than one-third of normative values, reflecting high diagnostic specificity (99%) and sensitivity (87%) in that subgroup, with reduced sensitivity in patients lacking cataplexy in the cited source framing.[20]

Evidence-based treatment

The primary goal of narcolepsy treatment is symptomatic management to enable participation in daily home and occupational activities.[20] Scheduled naps of approximately 20 minutes can reduce the frequency of sleep episodes during waking hours, and combining pharmacologic agents with two scheduled 15-minute naps per day and consistent nocturnal sleep hygiene has been reported to yield superior outcomes for subjective EDS and sleep attacks compared with pharmacotherapy alone.[20]

Pharmacotherapy is selected by dominant symptom phenotype. CNS stimulants and wake-promoting agents used for EDS include modafinil, armodafinil, methylphenidate, and solriamfetol in cited clinical summaries.[20] Randomized controlled trial data summarized in the source base report that modafinil reduces ESS by 4–6 points (p<0.001) and prolongs Maintenance of Wakefulness Test sleep latency by 3–5 minutes (p<0.001), with dosing initiated at 100 mg/day and titrated to 200–400 mg/day if needed.[11] Solriamfetol phase III trial summaries report mean MWT increases of 9.8 and 12.3 minutes (vs 2.1 minutes with placebo) and ESS reductions of 5.4 and 6.4 points (vs 1.6 points with placebo) for 150 mg and 300 mg doses, respectively.[11]

Pitolisant, a histamine H3 receptor inverse agonist, is approved for treating EDS or cataplexy in adults with narcolepsy in the cited review context, and the Harmony-CTP trial summary reports that pitolisant 36 mg/day reduced ESS by 5–7 points (p<0.001), prolonged MWT by 4–6 minutes (p<0.001), and decreased weekly cataplexy episodes by 75% (p<0.001).[4, 11] Sodium oxybate (gamma-hydroxybutyrate salt) is described as the only agent that simultaneously improves EDS, cataplexy, and disrupted nighttime sleep, with adult starting dose 4.5 g/night titratable to 9 g/night and long-term use associated with a significant sodium load of 1100–1640 mg/night (equating to 2.8–4.2 g salt nightly).[11]

Latest advances and controversies

Mechanism-based orexin receptor agonism is emerging as a pathophysiology-targeted strategy in narcolepsy, but development has raised hepatic safety concerns: a cited trial program was terminated early due to significant liver enzyme elevation and cases meeting Hy’s law criteria for drug-induced liver injury.[11] Across the class, current clinical studies of OX2R agonists lack head-to-head comparisons with comparable agents, limiting precise positioning in therapeutic algorithms even as proof-of-concept efficacy signals evolve.[11] Underdiagnosis and diagnostic delay remain persistent challenges in narcolepsy and other rare disorders, with reports of diagnostic delay reaching up to 14 years and negative consequences for quality of life, psychological distress, employment, and accident risk during the delay interval.[36]

Comorbidity and consequences

Narcolepsy confers elevated risk of motor vehicle accidents, with patients reported to be three to four times more likely to be involved in such incidents than the general population in cited clinical summaries.[20] Comorbidity is common: in one cohort analysis, 63.4% of patients presented with at least one comorbidity.[36]

Circadian Rhythm Sleep-Wake Disorders

Circadian rhythm sleep–wake disorders arise when the internal physiological clock is not synchronized with external stimuli, disrupting sleep–wake timing and other circadian-regulated activities.[37] These disorders can be classified as endogenous or exogenous, with endogenous disorders including delayed sleep–wake phase disorder (DSWPD), advanced sleep–wake phase disorder, non-24-hour sleep–wake rhythm disorder, and irregular sleep–wake rhythm disorder, and exogenous disorders associated with shift work or jet lag.[5]

Definition and epidemiology

DSWPD is characterized by a delay in the main sleep period with difficulty falling asleep and waking at socially appropriate times, and the delay is recurrent for at least three months and not better explained by another sleep, mental, or medical disorder.[12] An estimated 7–16% of adolescents and young adults are affected by delayed sleep phase syndrome in the cited summary base, supporting its relevance to adolescent and young adult health and policy discussions.[38]

Shift work sleep disorder is caused by recurring work schedules that conflict with natural sleep–wake patterns, and up to one-third of shift workers may experience persistent symptoms including delayed sleep initiation, fragmented sleep, excessive tiredness during wake periods, and compromised cognitive performance.[39]

Pathophysiology

The suprachiasmatic nucleus in the hypothalamus functions as the master clock that synchronizes internal processes with external events and receives light signals through the eyes, anchoring circadian entrainment to photic input.[5, 37] Melatonin secretion is closely related to the light–dark cycle and is described as a key regulator of the human biological clock, with levels rising after dusk and peaking between 2:00 and 4:00 a.m. (80–120 pg/mL) and falling during daylight (5–20 pg/mL).[5] Melatonin acts through receptors including MT1 and MT2, with MT1 activation described as mainly involved in REM sleep regulation and MT2 influencing NREM sleep, and melatonin synthesis is not confined to the pineal gland (also occurring in gastrointestinal cells, retina, and bone marrow).[5]

In DSWPD, delayed circadian phase assessment often relies on timing of minimum core body temperature or the evening melatonin surge (dim light melatonin onset, DLMO).[12] Delayed DLMO is described as highly sensitive and specific for DSWPD and useful for distinguishing DSWPD from conditions with extrinsic circadian or non-circadian causes (e.g., jet lag, primary insomnia).[12] DSWPD is also associated with decreased total sleep time and sleep efficiency and longer sleep onset latency even at preferred bedtimes, and homeostatic responses may differ such that patients are less likely to have daytime recovery sleep or to advance sleep timing after sleep deprivation.[12]

In shift workers, natural melatonin production is often misaligned or suppressed due to atypical light exposure, and melatonin interacts with MT1 and MT2 receptors in the suprachiasmatic nucleus to facilitate circadian realignment in mechanistic framing.[39]

Diagnostic criteria and workup

Clinical workup establishes that wake-up and sleep timings are regularly later than preferred or socially acceptable while sleep length remains within a typical range and sleep quality after sleep onset is otherwise normal, with symptom duration of at least three months.[38] Objective assessment can include sleep and activity recording, self-assessment of diurnal preference, and measurement of physiological phase markers, most often CTmin or DLMO timing.[12] DLMO is a commonly used measure to evaluate melatonin levels and can be leveraged to assess the timing of the endogenous circadian pacemaker in selected cases.[38] Actigraphy-based methods for assessing sleep patterns and circadian rhythms in delayed sleep phase syndrome are under development and validation, and EEG/PSG has been used to examine sleep stage transitions and spindles as neurophysiological markers in research contexts.[38]

Evidence-based treatment

Circadian interventions are phase-targeted, emphasizing controlled light exposure and timed melatonin. Morning exposure to bright light shortly after CTmin advances circadian phase and sleep period according to a phase response curve, whereas evening light can suppress melatonin production and impede sleep initiation.[12, 38] Exogenous melatonin administration is recommended for DSWPD under 2015 American Academy of Sleep Medicine guidelines in the cited review source, and melatonin shifts phase according to a phase response curve roughly inverse to that of light, with early evening dosing prior to DLMO advancing circadian phase.[12] Typical melatonin dosages for delayed sleep phase syndrome are described as 0.5 to 5 mg taken 30 minutes to 2 hours before bedtime, with timing relative to circadian phase remaining a major determinant of response.[12, 38]

In shift work contexts, subjective sleep quality improved when melatonin was taken approximately 30 to 60 minutes before the intended sleep period in the cited synthesis, with investigated doses ranging from 2 to 5 mg in immediate- and extended-release formulations.[39] Precision approaches are emerging: a randomized trial of personalized light therapy based on DLMO estimates derived from Apple Watch activity data (confirmed by in-lab DLMO) achieved a larger phase delay (mean 7.37 hours) than non-personalized control (mean 0.84 hours), with p=0.05, supporting a biomarker-anchored approach to circadian realignment in night shift workers.[40]

Pharmacologic sleep aids may be used to promote sleep, but evidence for hypnotics in DSWPD is limited, and the literature emphasizes that advancing sleep onset does not imply a true circadian phase shift or correction of sleep homeostasis.[12]

Comorbidity and consequences

Untreated delayed sleep phase syndrome can lead to impaired cognitive function and mood disturbances and increased risk of sleep-related problems such as sleep apnea and insomnia, and DSWPD is associated with insomnia and/or daytime sleepiness with resulting impairment of daytime function.[12, 38] Shift work–associated circadian disruption has been implicated in adverse outcomes including insulin resistance, cardiovascular disorders, gastrointestinal dysregulation, and weakened immune defenses, and reduced alertness contributes to workplace errors and accidents in safety-critical industries.[39] Epidemiological synthesis cited in the provided material indicates that shift workers have about a 40% higher risk of heart disease than day workers and that insufficient sleep impairs glucose metabolism and is associated with increased risk of type 2 diabetes.[41] Additional cited associations include shift work–related disruption of cytokine expression (pro-inflammatory IL-6 and anti-inflammatory IL-10), reproductive disturbances, immune vulnerability, and classification of circadian rhythm disturbances and shift work as carcinogenic factors by the International Agency for Research on Cancer in 2007.[41]

Parasomnias

Parasomnias involve unusual motor and vocal behaviors with emotional or sensory perceptions and are described within the ICSD-3 framework as disorders associated with dream mentation in relevant subtypes.[6] REM sleep behavior disorder is a prototypical REM-related parasomnia characterized by dream enactment caused by loss of physiological REM atonia and compromised generalized skeletal muscle atonia of REM sleep, permitting injurious acting-out of dreams.[6, 21]

Definition and epidemiology

ICSD-3-TR diagnostic framing requires repeated episodes of complex motor or vocal behaviors associated with vivid or violent dreams, polysomnographic confirmation of REM sleep without atonia, exclusion of other causes, and evidence of clinically significant consequences such as injury or disturbed sleep.[13] General-population prevalence is estimated at approximately 0.5–1%, with male predominance and peak incidence beyond age 50 in one synthesis.[13] In a pooled literature sample, 87.2% of cases were men and mean age was 63.6 years.[6] Community video-PSG prevalence estimates for isolated/idiopathic RBD include 1.06% and 1.23% in Switzerland and Japan, with additional estimates of 1.34% in a Korean cohort and 0.74% in a Spanish primary care cohort of older adults.[21]

RBD and its polysomnographic hallmark (loss of REM atonia) are common across synucleinopathies, occurring in 30–70% of Parkinson disease, 70–80% of dementia with Lewy bodies, and 70–90% of multiple system atrophy, and in many cases RBD precedes other manifestations, supporting the isolated/idiopathic RBD construct as prodromal neurodegeneration.[42]

Pathophysiology

The core mechanism is failure of REM-atonia generation, with compromised generalized skeletal muscle atonia allowing dream enactment behaviors.[21] Longitudinal studies on iRBD have found that over 90% of patients eventually phenoconvert to an overt α-synucleinopathy, consistent with iRBD as a prodromal window for neurodegenerative disease biology and intervention trials.[21] Neuroimaging evidence suggests alterations in dopaminergic and cholinergic systems and that RBD may represent a multisystem neurodegenerative process involving the nigrostriatal system, limbic system, and cortex, with longitudinal ordering in iRBD suggesting early striatal synaptic dopaminergic dysfunction followed by abnormal iron metabolism in substantia nigra pars compacta coupled with neuromelanin changes.[43]

Diagnostic criteria and workup

Diagnostic criteria require repeated episodes of sleep-related vocalization or complex motor behaviors, documentation that behaviors occur during REM sleep (preferably by video-polysomnography), PSG demonstration of REM sleep without atonia, and exclusion of other sleep or mental disorders explaining the disturbance.[21] At least one night of video-PSG is required in many research definitions, and video-PSG is described as the gold standard for differential diagnosis between RBD and other sleep disorders.[6] Differential diagnosis includes NREM parasomnias, obstructive sleep apnea pseudo-RBD, periodic limb movement disorder pseudo-RBD, and nocturnal seizures.[21] Dream-content assessment by retrospective recall is vulnerable to recall bias, limiting inference about dream frequency and content without prospective methods.[6]

Evidence-based treatment

First-line management is injury prevention through environmental safety: a safe sleeping environment must be maintained to prevent potentially injurious nocturnal behaviors.[21] The American Academy of Sleep Medicine provides conditional recommendations for pharmacotherapy options in adults with iRBD or secondary RBD due to medical conditions, including clonazepam, immediate-release melatonin, and pramipexole (for iRBD).[21] Longitudinal evidence summarized in the cited review indicates that melatonin and clonazepam use is associated with suspension of frightening violent dreams and nightmares during treatment.[6]

Latest advances and controversies

RBD offers an opportunity to test potential treatments at the earliest stages of synucleinopathy, but disease-modifying therapies for synucleinopathy patients have failed to date in the cited perspective, potentially because pathology at clinical diagnosis is already too advanced to modify.[24] Biomarker development remains a bottleneck because there are no established or widely used biomarkers for detecting prodromal synucleinopathies in the cited synthesis, despite the high predictive value of iRBD for Parkinson disease phenoconversion (likelihood ratio 130) and strong conversion rates in meta-analysis (33% at 5 years, 82% at 10.5 years, 97% at 14 years).[21, 24] Phenotype heterogeneity remains a controversy: antidepressant medications are associated with RBD presenting earlier and in women, and it remains unknown whether antidepressants unmask typical neuropathologic processes or represent a distinct pathophysiologic pathway in some cases.[24]

7. Sleep-Related Movement Disorders

RLS (Willis–Ekbom disease) is a chronic sensorimotor disorder in which symptoms worsen during rest and show circadian predominance in the evening and night, reflected in mechanistic framing as a circadian dysfunction of sensorimotor integration.[15] Many individuals with RLS also experience periodic limb movements of sleep, occurring in up to 80–90% of patients and contributing to sleep fragmentation, though periodic limb movements are not specific to RLS.[7]

Definition and epidemiology

Population prevalence estimates vary with diagnostic rigor. North American population studies report that roughly 10% of adults experience RLS symptoms, with around 2–3% experiencing clinically significant symptoms requiring treatment.[7] A pooled prevalence estimate reported in one updated synthesis was 3% (95% CI 1.4–3.8), with prevalence differing between males (2.8%) and females (4.7%).[44] RLS is more common in women and increases with age, and pregnancy is a strong precipitant with approximately one-third of women experiencing symptoms in the third trimester.[7, 15] RLS is substantially more common in chronic kidney disease populations, with dialysis prevalence commonly 15–30% and RLS being two to three times more common in CKD than in the general population, while ESRD prevalence ranges from 15% to 45% and uremic RLS is associated with chronic insomnia affecting up to 70% of cases.[14, 45]

Pathophysiology

Current models emphasize two interconnected central mechanisms: brain iron deficiency and dopaminergic dysfunction.[7] Dopaminergic agents and dopamine agonists improve symptoms, supporting dopaminergic involvement, but the mechanistic framing is more complex than simple deficiency, with hypotheses spanning altered dopamine synthesis and reuptake with reduced D2 receptor sensitivity and, alternatively, presynaptic hyperdopaminergic states with compensatory postsynaptic receptor downregulation leading to relative evening and nighttime dopamine deficit and symptom emergence.[15, 44, 46]

Iron biology in RLS is clinically challenging because serum markers such as ferritin and percent transferrin saturation do not accurately reflect brain iron stores, and serum iron deficiency is present in only 25–44% of patients in one cited synthesis, necessitating cautious interpretation of peripheral iron indices.[15] CSF studies cited in the source base show higher CSF transferrin and lower ferritin in RLS versus controls despite normal serum ferritin, consistent with central iron deficiency, and these findings have been interpreted as suggesting CSF ferritin and transferrin as promising biomarkers for RLS diagnosis and management.[15] Genetic predisposition is substantial, with 83% concordance in monozygotic twins and genome-wide association studies identifying multiple implicated loci and genes (including BTBD9, MEIS1, MAP2K5, PTPRD, TOX3) contributing to population genetic risk in one cited summary.[15]

Beyond iron and dopamine, additional proposed mechanisms include hypoxic-state activation with elevated hypoxia-inducible factors and VEGF, a hypo-adenosinergic state with low adenosine levels promoting hyperarousal and activating dopaminergic and hypoxic pathways, and hyperglutamatergic neurotransmission supported by elevated thalamic glutamate and therapeutic effects of α2δ ligands.[7, 15, 46]

Diagnostic criteria and workup

RLS diagnosis is clinical and relies on meeting five essential IRLSSG criteria, including an urge to move the legs with unpleasant sensations, worsening during rest, relief with movement, evening or nighttime predominance, and exclusion of mimics and alternative explanations (e.g., leg cramps, arthritis, positional discomfort, anxiety).[15, 44, 46] For rapid screening, the IRLSSG recommends a single validated question regarding unpleasant restless feelings in the legs during evening relaxation or attempting sleep that are relieved by walking or movement, reported to have 100% sensitivity and 96.8% specificity in large-scale screenings.[15]

Initial management includes measuring serum ferritin and transferrin-percent saturation, with iron replacement indicated when these measures are below the low-to-normal range and with a cited target strategy of raising ferritin above 75 ng/mL.[14, 46] Actigraphy is no longer recommended for assessing periodic limb movements of sleep because of accuracy concerns, and polysomnography is the only recommended option for periodic limb movement assessment, though it is not part of the standard diagnostic process for RLS itself.[46]

Evidence-based treatment

Treatment should be initiated when symptoms impair quality of life, daytime functioning, social functioning, or sleep.[46] Iron deficiency is a strong risk factor for RLS, and multiple studies demonstrate that iron supplementation improves characteristic neurological symptoms in cited syntheses.[44] Clinical guidelines recommend IV ferric carboxymaltose (FCM) for adults with moderate-to-severe RLS with serum ferritin ≤300 μg/L and TSAT below 45%, and both oral and IV iron therapies should be limited to patients with TSAT <45% to avoid iron overload in the cited guidance framing.[15] IV iron therapy, particularly FCM, is described as having superior efficacy, including effectiveness even when serum ferritin exceeds 75 μg/L, whereas oral iron can provide little benefit and is limited by absorption and compliance issues including gastrointestinal discomfort.[15]

The long-standing use of dopamine agonists has been re-evaluated because augmentation (iatrogenic worsening) accumulates over time; dopamine agonists previously considered first-line are now conditionally recommended due to augmentation risk in one updated review synthesis, with augmentation rates reported as <10% in short-term studies and increasing with longer durations and varying by drug, dose, study type, and evaluation criteria.[44, 46] In uremic RLS/ESRD, augmentation can occur in 40–70% of patients receiving dopamine agonists and up to 80% of those treated with levodopa, often rendering patients worse than pretreatment baseline in the cited summary.[45]

α2δ ligands (gabapentinoids) are emphasized as alternatives with minimal augmentation risk. In ESRD, α2δ ligands exhibit minimal augmentation risk and pregabalin is described as maintaining a favorable safety profile with straightforward dose adjustment for renal clearance.[45] In a randomized double-blind placebo-controlled ESRD uremic RLS trial summary, pregabalin produced median IRLSSG severity reductions of −5.0 points at week 6 versus 0.0 with placebo (p≤0.001) and −9.0 points at week 12 versus −2.0 with placebo (p≤0.001), with mild sedation reported by 28% versus 8% and no serious adverse events attributable to pregabalin.[45] Second-line strategies in CKD-associated RLS include IV iron for those intolerant of oral iron or experiencing augmentation and opioid therapies such as tramadol, oxycodone, and methadone in cited guidance summaries.[14]

Latest advances and controversies

Diagnostic rigor drives prevalence heterogeneity: the revised 2012 IRLSSG criteria emphasized differentiating true RLS from mimics by introducing a fifth element, and prevalence tends to be lower in studies using more accurate diagnostic methods and in East and Southeast Asia compared with other regions in one synthesis.[44] Treatment durability remains unresolved: long-term safety and efficacy data for repeated iron treatments, particularly IV iron, are sparse in the cited review, and nonresponse despite ferritin normalization (nearly two-thirds continuing symptoms) indicates contributors beyond peripheral iron in some patients.[15] Mechanistic biomarkers may eventually guide therapy selection: pregabalin administration produced a distinctive cortical oscillatory modulation pattern and the correspondence between molecular mechanism, neural signature, and clinical efficacy suggests cortical oscillatory profiling as a potential preclinical screening tool for RLS therapeutic candidates.[45]

Comorbidity and consequences

In uremic RLS, chronic insomnia affects up to 70% of cases and sleep deprivation cascades into daytime fatigue, depression, anxiety, and marked functional impairment.[45] Cohort studies in dialysis populations suggest that uremic RLS independently predicts cardiovascular events and increased mortality, and CKD-associated RLS is associated with increased mortality, increased cardiovascular accident incidence, depression, insomnia, and impaired quality of life compared with CKD without RLS, though careful studies remain needed in this area.[14, 45]

8. Cross-Cutting Advances

The expansion of home-based sleep monitoring is driven by the clinical need for scalable objective measurement beyond the laboratory, given that PSG remains the gold standard but is limited by complexity, high cost (USD 1500–2000 per night in the United States), need for qualified personnel, and an artificial clinical setting.[1] Research on home-based sleep monitoring has converged on analytical reviews of wearable and “nearable” devices and empirical validation studies across clinical and consumer settings, but insufficient standardization of validation protocols remains a central limitation.[1]

Actigraphy offers longitudinal monitoring but infers sleep continuity based on assumptions of sleep during a time window and movement thresholds for awakening; it typically has high sensitivity for detecting sleep (>90%) but low specificity for wakefulness (20–70%), which can be especially misleading in populations with frequent pre- and mid-sleep wakefulness (e.g., chronic pain).[23] Complementary wearable EEG approaches include devices such as the Dreem Headband (five dry electrodes positioned at F7, F8, Fpz, O1, O2; sampling 250 Hz; integrated accelerometer and pulse oximeter) and the Sleep Profiler X4 (frontopolar electrodes AF7, AF8, Fpz; cloud data transmission; accelerometer for head movement).[1]

Algorithmic limitations matter for clinical interpretation: systematic overestimation of REM and underestimation of deep N3 sleep have been observed in re-evaluation settings, and in isolated RBD work algorithms were highly sensitive to REM episodes but had low specificity for microarousals in one cited synthesis.[1] Despite these limitations, wearable PSG devices combined with machine learning can assess sleep continuity, sleep stages, and EEG power spectrum with similar accuracy (>80%) to lab-based PSG in cited summaries, motivating continued development toward multisensor integration, open validation protocols, and AI analytics that shift from retrospective assessment to risk forecasting and personalized recommendations.[1, 23]

Sleep disturbance is tightly linked to other symptom domains through bidirectional relationships, exemplified by chronic pain, where poor sleep exacerbates pain and pain disrupts sleep, and sleep deprivation can increase pain sensitivity and hinder pain modulation.[23]

9. Diagnostic Tools at a Glance

Diagnostic tool selection should be matched to the suspected disorder and pretest probability, recognizing that each instrument captures different physiological dimensions and has disorder-specific blind spots.[10, 23] PSG remains the reference standard for comprehensive evaluation of sleep stages, arousals, respiratory events, and comorbid sleep disorders, while HSAT improves access for uncomplicated high-pretest-probability OSA but can underestimate severity in mild disease because EEG sleep staging is absent.[10] For circadian disorders, DLMO is emphasized as a high-utility phase biomarker with sensitivity and specificity for DSWPD and can be paired with sleep diaries and actigraphy for rhythm documentation.[12, 38] For parasomnias such as RBD, video-PSG is the gold standard to document REM sleep without atonia and to exclude mimics and pseudo-RBD presentations.[6, 21]

The table below summarizes selected tools using only evidence-supported attributes from the provided sources.

10. Therapeutics Pipeline

Two mechanistically anchored pipelines dominate the cited 2024–2026 evidence base: orexin-pathway modulation and incretin-based disease modification for obesity-associated OSA.[9, 16] In insomnia, DORAs are positioned as a major recent pharmacologic development, with ongoing exploration of novel agents such as TS-142 designed for fast absorption and short plasma half-life, although early trial generalizability limitations have been noted due to high screen-failure rates and small completion numbers.[17, 30] In hypersomnolence, orexin receptor agonist development has faced class safety constraints exemplified by termination of a trial program due to liver enzyme elevation and Hy’s law–level drug-induced liver injury signals, underscoring the need for hepatic safety monitoring as efficacy signals evolve.[11]

In OSA, the SURMOUNT-OSA phase 3 program established tirzepatide’s large AHI reductions at 52 weeks and stringent combined response rates, and one review source reports FDA approval for obesity-associated obstructive sleep apnea syndrome in June 2024, supporting a new era of pharmacologic disease modification in obesity-driven OSA phenotypes.[19, 34] Mechanistic uncertainty persists regarding the pathways by which GLP-1 signaling influences respiratory control and upper-airway muscle tone, and long-term OSA-specific safety and efficacy remain incompletely characterized in cited reviews despite robust 52-week data.[3]

Implementation innovations also function as a therapeutic “pipeline” by enhancing delivery and adherence: telemonitoring provides real-time feedback and improves long-term CPAP usage, while virtual care pathways combining questionnaires, HSAT, remote initiation, and digital adherence support may expand access to effective therapies when resource constraints limit specialist availability.[10]

11. Practice Points and Knowledge Gaps

Practice recommendations must balance operational diagnostic criteria with pathophysiology-informed treatment selection and explicit management of comorbidity and downstream risk.[8, 10, 18] The points below emphasize actionable items supported by the cited evidence.

Practice points

• Diagnose chronic insomnia using ICSD-3/DSM-5 frequency and duration thresholds (≥3 nights/week for ≥3 months) and document daytime manifestations and adequate sleep opportunity.[2, 8]
• Use structured clinical history for insomnia to assess sleep-initiation and maintenance problems, maladaptive habits, daytime impairment, and comorbid contributors (mood disorders, pain, RLS, OSA).[18]
• Prefer CBT-I as first-line insomnia treatment because multiple major guidelines strongly recommend it and evidence summaries emphasize superior long-term efficacy with few adverse effects.[18]
• Avoid routine PSG as the initial objective test for insomnia unless symptoms suggest another sleep disorder requiring objective exclusion (e.g., OSA, parasomnia).[18]
• When prescribing daridorexant, apply label-aligned dosing guidance (50 mg within 30 minutes of bedtime if ≥7 hours remain; reduce to 25 mg in moderate hepatic impairment; avoid in severe impairment).[28]
• In suspected OSA, use STOP-Bang or NoSAS for case finding but confirm with PSG or HSAT depending on complexity and pretest probability, recognizing HSAT’s reduced sensitivity in mild OSA and tendency to underestimate severity without EEG staging.[10]
• Treat OSA with CPAP as the cornerstone therapy while explicitly addressing adherence barriers; interpret cardiovascular protection as adherence-dependent, with benefit observed when CPAP use exceeds 4 hours/night in pooled analyses.[3, 10]
• For PAP-intolerant moderate-to-severe OSA without complete concentric palatal collapse, consider hypoglossal nerve stimulation while counseling about surgical invasiveness, cost, and eligibility restrictions.[10]
• In obesity-associated moderate-to-severe OSA, consider tirzepatide where appropriate, given 52-week AHI reductions of −25.3 and −29.3 events/hour in phase 3 trials and stringent combined response criteria met by up to 50.2%, while monitoring gastrointestinal adverse events and rare serious adverse events such as pancreatitis noted in trial reporting.[19]
• For suspected narcolepsy with persistent severe EDS >3 months, perform overnight PSG followed by MSLT and apply diagnostic thresholds (mean sleep latency <8 minutes and ≥2 SOREMPs); consider CSF hypocretin-1 testing in cataplexy-associated or equivocal cases.[20]
• For DSWPD, document persistent phase delay for ≥3 months and consider DLMO measurement as a sensitive and specific biomarker to distinguish intrinsic DSWPD from extrinsic circadian or non-circadian causes; treat with timed morning bright light and appropriately timed melatonin.[12]
• For RBD, prioritize injury prevention and confirm diagnosis with video-PSG demonstrating REM sleep without atonia; counsel that iRBD carries high long-term phenoconversion risk (meta-analysis: 97% by 14 years).[6, 21]
• For RLS, confirm the five IRLSSG essential criteria, screen efficiently with the single validated IRLSSG question when appropriate, and assess iron status with ferritin and TSAT before selecting therapy.[14, 15, 46]

Knowledge gaps

• Real-world validation of DORA effectiveness and safety remains a stated need despite guideline recognition of DORAs as a major pharmacologic advance in insomnia.[17]
• Lack of direct head-to-head comparisons across DORAs limits definitive within-class selection strategies for insomnia treatment.[2]
• Mechanistic pathways linking GLP-1 signaling to respiratory control and upper-airway muscle tone in OSA remain unclear, and long-term efficacy and safety data for GLP-1 receptor agonists in OSA are limited in cited reviews.[3]
• CPAP cardiovascular outcome inconsistency persists, requiring continued focus on adherence and on trial designs that adequately capture adherence-modified effects.[10]
• There are no established or widely used biomarkers for detecting prodromal synucleinopathies despite iRBD’s strong predictive value, limiting prevention-trial enrichment outside specialized cohorts.[21, 24]

Validation standardization of wearable sleep technologies remains insufficient, and algorithmic biases (REM overestimation, N3 underestimation; microarousal detection limitations) risk distorting clinical interpretation without rigorous benchmarking.[1]

Conclusions

The 2026 sleep-medicine landscape is characterized by mechanistically aligned pharmacotherapy (orexin-pathway modulation for insomnia; incretin-based disease modification for obesity-associated OSA; wake-promoting agents and emerging orexin agonism for hypersomnolence), endotype-driven conceptualization of OSA pathophysiology, and biomarker-anchored circadian diagnostics (DLMO) that enable more precise interventions.[9, 10, 12, 16, 17] At the same time, practice remains constrained by implementation gaps (underdiagnosis, limited access to PSG, adherence barriers to CPAP), incomplete mechanistic clarity for key emerging therapies, and the absence of widely deployed prodromal biomarkers for neurodegenerative risk states such as iRBD, reinforcing the need for integrated clinical pathways that combine structured clinical phenotyping with validated objective tools and longitudinal risk counseling.[1, 3, 18, 24]

Glossary of Abbreviations

• AHI: apnea–hypopnea index, reported as events per hour in clinical trials and used to quantify treatment-associated change in OSA severity.[19]
• CBT-I: cognitive behavioral therapy for insomnia, recommended as first-line treatment by major sleep guidelines.[18]
• CPAP: continuous positive airway pressure, the cornerstone and gold-standard treatment for obstructive sleep apnea.[3, 10]
• CSF: cerebrospinal fluid, used for hypocretin-1 measurement in narcolepsy type 1 diagnosis and phenotyping.[11, 20]
• DLMO: dim light melatonin onset, a phase marker described as highly sensitive and specific for DSWPD and used in personalized light therapy protocols.[12, 40]
• DORA: dual orexin receptor antagonist, a class that blocks OX1R and OX2R to reduce wakefulness and promote sleep in insomnia disorder pharmacotherapy.[9, 26]
• DSWPD: delayed sleep–wake phase disorder, characterized by delayed sleep timing recurring for at least 3 months and not better explained by another disorder.[12]
• EDS: excessive daytime sleepiness, a core symptom prompting narcolepsy workup and central hypersomnolence assessment.[20]
• ESS: Epworth Sleepiness Scale, a validated questionnaire used to quantify subjective sleepiness in narcolepsy and OSA studies.[19, 20]
• HSAT: home sleep apnea testing, accepted for uncomplicated adults with suspected moderate-to-severe OSA but less sensitive for mild OSA and may underestimate severity without EEG sleep staging.[10]
• IRLSSG: International Restless Legs Syndrome Study Group, which defines essential diagnostic criteria and a validated single screening question for RLS.[15]
• LPS: latency to persistent sleep, used as an endpoint in insomnia trials assessing sleep-onset improvement.[29, 47]
• MSLT: Multiple Sleep Latency Test, performed after overnight PSG and used to confirm narcolepsy (mean sleep latency <8 minutes and ≥2 SOREMPs).[20]
• OSA: obstructive sleep apnea, characterized by repetitive upper-airway collapse during sleep with intermittent hypoxia and fragmented sleep.[3]
• PSG: polysomnography, the gold standard for comprehensive sleep assessment and for confirming RBD via REM sleep without atonia.[10, 21]
• RBD: REM sleep behavior disorder, a parasomnia characterized by dream enactment due to loss of physiological REM atonia.[6]
• RLS: restless legs syndrome, a sensorimotor disorder diagnosed clinically by IRLSSG essential criteria and associated with periodic limb movements of sleep in many patients.[7, 15]
• SOREMP: sleep-onset REM period, a diagnostic feature on MSLT for narcolepsy when ≥2 are observed with short mean sleep latency.[20]
• WASO: wake after sleep onset, a sleep maintenance parameter used as an outcome in insomnia pharmacotherapy trials.[28, 29]