Differences in findings of nocturnal polysomnography and multiple sleep latency test between narcolepsy and idiopathic hypersomnia

The Role of Sodium Oxybate in Idiopathic Hypersomnia: A Case Report Showing Improvement of Excessive Daytime Sleepiness and Reduced Symptoms

Our aim is to report the clinical profile and outcome of patients diagnosed with idiopathic hypersomnia (IH). Idiopathic hypersomnolence is a complex, debilitating, and uncommon sleep disorder manifested mainly by chronic excessive daytime sleepiness (EDS). This paper reports on the treatment of a patient with idiopathic hypersomnia who was treated with low sodium oxybate (LXB) due to a lack of response to the first-line drug modafinil. This patient, who presented with worsening excessive daytime sleepiness, sleep drunkenness, and sleep disturbances, was diagnosed with idiopathic hypersomnia by overnight polysomnography (PSG) and a multiple sleep latency test (MSLT). Stimulant agent modafinil was prescribed along with sleep hygiene education. Her symptoms did not respond to modafinil, and she was switched to a recently approved newer medication, i.e., low sodium oxybate.

Central Disorders of Hypersomnolence

OBJECTIVE

The goals of this article are to describe the clinical approach to and management of patients with central disorders of hypersomnolence, and to understand and differentiate available diagnostic tools.

LATEST DEVELOPMENTS

Updated clinical practice guidelines for the treatment of central disorders of hypersomnolence and narcolepsy specifically highlight new treatment options. Approval for a lower-sodium oxybate formulation that contains 92% less sodium than the standard sodium oxybate for the treatment of narcolepsy and idiopathic hypersomnia adds to the number of medications available for these disorders, allowing for a more tailored management of symptoms.

ESSENTIAL POINTS

Central disorders of hypersomnolence are characterized by excessive daytime sleepiness that impacts daily functions. These disorders can be differentiated by obtaining a detailed clinical sleep history and by a thoughtful interpretation of sleep diagnostic testing. Tailoring treatment approaches to meet the needs of individuals and accounting for medical and psychiatric comorbidities may improve quality of life.

Narcolepsy and Idiopathic Hypersomnia

Narcolepsy types 1 and 2 and idiopathic hypersomnia are primary Central Nervous System (CNS) disorders of hypersomnolence characterized by profound daytime sleepiness and/or excessive sleep need. Onset of symptoms begins typically in childhood or adolescence, and children can have unique presentations compared with adults. Narcolepsy type 1 is likely caused by immune-mediated loss of orexin (hypocretin) neurons in the hypothalamus; however, the causes of narcolepsy type 2 and idiopathic hypersomnia are unknown. Existing treatments improve daytime sleepiness and cataplexy but there is no cure for these disorders.

Precision Medicine for Idiopathic Hypersomnia

Idiopathic hypersomnia (IH) includes a clinical phenotype resembling narcolepsy (with repeated, short restorative naps), and a phenotype with an excess of sleep, sleep drunkenness, drowsiness, and infrequent long, nonrestorative naps. Sleep tests reflect this heterogeneity. MSLTs are greater than 8 min in 2/3 of the cases and poorly repeatable. Sleep excess is better captured by extended monitoring identifying 11 to 16h of sleep/24 h. Patients with IH are young and more often female. Possible mechanisms of IH include deficiencies in arousal systems, inappropriate stimulation of sleep-inducing systems, and long biological night. Treatments now include robust studies of modafinil, clarithromycin, and sodium oxybate.

Metabolic-Syndrome-Related Comorbidities in Narcolepsy Spectrum Disorders: A Preliminary Cross-Sectional Study in Japan

Narcolepsy types 1 (NT1) and 2 (NT2) and idiopathic hypersomnia (IH) are thought to be a disease continuum known as narcolepsy spectrum disorders (NSDs). This study aimed to assess the prevalence of and factors associated with metabolic-syndrome-related disorders (MRDs) among patients with NSD. Japanese patients with NSD (NT1, n = 94; NT2, n = 83; and IH, n = 57) aged ≥35 years were enrolled in this cross-sectional study. MRD was defined as having at least one of the following conditions: hypertension, diabetes, or dyslipidemia. Demographic variables and MRD incidence were compared among patients in the respective NSD categories. Multivariate logistic regression analysis was used to investigate the factors associated with MRDs. Patients with NT1 had a higher body mass index (BMI) and incidence of MRD than that had by those with NT2 or IH. Age, BMI, and the presence of OSA were significantly associated with the incidence of MRD in NSDs. Age and BMI in NT1, BMI and human leukocyte antigen (HLA)-DQB1*06:02 positivity in NT2, and only age in IH were factors associated with the incidence of MRD. Obesity should be carefully monitored in narcolepsy; however, NT2 with HLA-DQB1*06:02 positive should be followed up for the development of MRD even without obesity.

Disrupted nighttime sleep and sleep instability in narcolepsy

STUDY OBJECTIVES

This review aimed to summarize current knowledge about disrupted nighttime sleep (DNS) and sleep instability in narcolepsy, including self-reported and objective assessments, potential causes of sleep instability, health consequences and functional burden, and management.

METHODS

One hundred two peer-reviewed publications from a PubMed search were included.

RESULTS

DNS is a key symptom of narcolepsy but has received less attention than excessive daytime sleepiness and cataplexy. There has been a lack of clarity regarding the definition of DNS, as many sleep-related symptoms and conditions disrupt sleep quality in narcolepsy (eg, hallucinations, sleep paralysis, rapid eye movement sleep behavior disorder, nightmares, restless legs syndrome/periodic leg movements, nocturnal eating, sleep apnea, depression, anxiety). In addition, the intrinsic sleep instability of narcolepsy results in frequent spontaneous wakings and sleep stage transitions, contributing to DNS. Sleep instability likely emerges in the setting of orexin insufficiency/deficiency, but its exact pathophysiology remains unknown. DNS impairs quality of life among people with narcolepsy, and more research is needed to determine its contributions to cardiovascular risk. Multimodal treatment is appropriate for DNS management, including behavioral therapies, counseling on sleep hygiene, and/or medication. There is strong evidence showing improvement in self-reported sleep quality and objective sleep stability measures with sodium oxybate, but rigorous clinical trials with other pharmacotherapies are needed. Treatment may be complicated by comorbidities, concomitant medications, and mood disorders.

CONCLUSIONS

DNS is a common symptom of narcolepsy deserving consideration in clinical care and future research.

CITATION

Maski K, Mignot E, Plazzi G, Dauvilliers Y. Disrupted nighttime sleep and sleep instability in narcolepsy. J Clin Sleep Med. 2022;18(1):289-304.

Animal models of narcolepsy and the hypocretin/orexin system: Past, present, and future

Animal models have advanced not only our understanding of the etiology and phenotype of the sleep disorder narcolepsy but have also informed sleep/wake regulation more generally. The identification of an inheritable narcolepsy phenotype in dogs in the 1970s allowed the establishment of a breeding colony at Stanford University, resulting in studies that provided the first insights into the genetics and neurotransmitter systems that underlie cataplexy and rapid-eye movement sleep atonia. Although the discovery of the hypocretin/orexin neuropeptides in 1998 initially seemed unrelated to sleep/wake control, the description of the phenotype of the prepro-orexin knockout (KO) mouse as strongly resembling cataplexy, the pathognomonic symptom of narcolepsy, along with identification of a mutation in hypocretin receptor-2 gene as the source of canine narcolepsy, unequivocally established the relationship between this system and narcolepsy. The subsequent discovery of hypocretin neuron degeneration in human narcolepsy demystified a disorder whose etiology had been unknown since its initial description 120 years earlier. These breakthroughs prompted the development of numerous other animal models that have allowed manipulation of the hypocretin/orexin system, thereby advancing our understanding of sleep/wake circuitry. While animal models have greatly informed understanding of this fascinating disorder and the role of the hypocretin/orexin system in sleep/wake control, the question of why these neurons degenerate in human narcolepsy is only beginning to be understood. The development of new immune-mediated narcolepsy models are likely to further inform the etiology of this sleep disorder and animal models will undoubtedly play a critical role in the development of novel narcolepsy therapeutics.

Reliability and validity of the Chinese version of Narcolepsy Severity Scale in adult patients with narcolepsy type 1

OBJECTIVE

To evaluate reliability and validity of the Chinese version of Narcolepsy Severity Scale (NSS) in adult patients with narcolepsy type 1 (NT1).

METHODS

One hundred and fifty-one adult patients (≥18 years) with NT1 were recruited. All filled out the 15-item Chinese version of NSS. Item analysis included critical ratio and correlation analysis. The validity of NSS was assessed by exploratory factor analysis, discriminant validity and convergent validity. Reliability of NSS was assessed by Cronbach's α coefficient, spilt-half reliability and test-retest reliability.

RESULTS

Critical value of all 15 items ranged from 3.01 to 13.36. Each item was significantly correlated with the total score by a correlation coefficient (r) ranging from 0.219 to 0.700. Three common domains were extracted and 15 items explained 54.86% of the total variance. There was a shift in domains compared to the English version likely due to cultural differences. Cronbach's α coefficient for the total scale of 15 items was 0.821 and for three factors was 0.726, 0.748 and 0.760 respectively. The NSS had good correlation with Epworth sleepiness scale scores, Insomnia severity index scores and moderate correlation with mean the sleep latency of polysomnographic recording, and European Quality of Life-5 Dimensions Questionnaire. The Chinese version of NSS showed good spilt-half reliability and test-retest reliability.

CONCLUSION

The Chinese version of NSS shows satisfactory psychometric properties with good validity and reliability. It is applicable to evaluate the severity and consequences of symptoms in Chinese adult patients with NT1.

Cardiovascular disorders in narcolepsy: Review of associations and determinants

Narcolepsy type 1 (NT1) is a lifelong disorder of sleep-wake dysregulation defined by clinical symptoms, neurophysiological findings, and low hypocretin levels. Besides a role in sleep, hypocretins are also involved in regulation of heart rate and blood pressure. This literature review examines data on the autonomic effects of hypocretin deficiency and evidence about how narcolepsy is associated with multiple cardiovascular risk factors and comorbidities, including cardiovascular disease. An important impact in NT1 is lack of nocturnal blood pressure dipping, which has been associated with mortality in the general population. Hypertension is also prevalent in NT1. Furthermore, disrupted nighttime sleep and excessive daytime sleepiness, which are characteristic of narcolepsy, may increase cardiovascular risk. Patients with narcolepsy also often present with other comorbidities (eg, obesity, diabetes, depression, other sleep disorders) that may contribute to increased cardiovascular risk. Management of multimorbidity in patients with narcolepsy should include regular assessment of cardiovascular health (including ambulatory blood pressure monitoring), mitigation of cardiovascular risk factors (eg, cessation of smoking and other lifestyle changes, sleep hygiene, and pharmacotherapy), and prescription of a regimen of narcolepsy medications that balances symptomatic benefits with cardiovascular safety.

Idiopathic Hypersomnia and Other Hypersomnia Syndromes

There are numerous disorders of known or presumed neurologic origin that result in excessive daytime sleepiness, collectively known as the central disorders of hypersomnolence. These include narcolepsy types 1 and 2, idiopathic hypersomnia, Kleine-Levin syndrome, and hypersomnia due to or associated with medical disease, neurologic disease, psychiatric disease, medications or substances, and insufficient sleep durations. This chapter focuses on the treatment of nonnarcoleptic hypersomnia syndromes, from those that are commonly encountered in neurologic practice, such as hypersomnia due to Parkinson's disease, to those that are exceedingly rare but present with dramatic manifestations, such as Kleine-Levin syndrome. The level of evidence for the treatment of sleepiness in these disorders is generally lower than in the well-characterized syndrome of narcolepsy, but available clinical and randomized, controlled trial data can provide guidance for the management of each of these disorders. Treatments vary by diagnosis but may include modafinil/armodafinil, traditional psychostimulants, solriamfetol, pitolisant, clarithromycin, flumazenil, sodium oxybate, melatonin, methylprednisolone, and lithium.

Central Disorders of Hypersomnolence

PURPOSE OF REVIEW

This article discusses the central disorders of hypersomnolence, a group of disorders resulting in pathologic daytime sleepiness, particularly narcolepsy type 1 and narcolepsy type 2, idiopathic hypersomnia, and Kleine-Levin syndrome. Disease features, diagnostic testing, epidemiology, pathophysiology, and treatment are reviewed.

RECENT FINDINGS

Increasing evidence implicates autoimmunity in narcolepsy type 1, including a strong association with human leukocyte antigen-DQB1*06:02, association with a polymorphism in the T-cell receptor alpha locus in genome-wide association, and the identification of autoreactive T cells in patients with this type of narcolepsy. In contrast, the cause or causes of narcolepsy type 2 and idiopathic hypersomnia are unknown. Multiple treatment options exist, including two medications approved for the treatment of narcolepsy by the US Food and Drug Administration (FDA) in 2019. These include solriamfetol, a dopamine- and norepinephrine-reuptake inhibitor, and pitolisant, an H3-inverse agonist/antagonist that increases histaminergic neurotransmission.

SUMMARY

The central disorders of hypersomnolence all cause severe sleepiness but can be differentiated based on ancillary symptoms, diagnostic testing, and pathophysiology. It is important that these disorders are identified because multiple treatments are available to improve functioning and quality of life.

The multiple sleep latency test

The measurement of daytime sleepiness is important in the evaluation of patients with excessive sleepiness. The multiple sleep latency test (MSLT) is an objective test that measures the tendency to fall asleep under controlled conditions. It is based on the notion that sleep latency reflects underlying physiological sleepiness. The MSLT consists of four to five naps given 2h apart during the day, following a standardized procedure. The mean sleep latency from all naps is used as the measure of sleepiness. The test has been shown to be valid and reliable and is part of the diagnostic criteria for narcolepsy and idiopathic hypersomnia. However, the MSLT is affected by numerous variables including insufficient sleep, drugs, activity, and arousal level. Adherence to the established protocol is necessary to limit the effect of these extraneous factors on the MSLT. While the test is a valuable and widely used diagnostic tool for narcolepsy and idiopathic hypersomnia, the use of MSLT in other sleep disorders is not well established.

Exploring the clinical features of narcolepsy type 1 versus narcolepsy type 2 from European Narcolepsy Network database with machine learning

Narcolepsy is a rare life-long disease that exists in two forms, narcolepsy type-1 (NT1) or type-2 (NT2), but only NT1 is accepted as clearly defined entity. Both types of narcolepsies belong to the group of central hypersomnias (CH), a spectrum of poorly defined diseases with excessive daytime sleepiness as a core feature. Due to the considerable overlap of symptoms and the rarity of the diseases, it is difficult to identify distinct phenotypes of CH. Machine learning (ML) can help to identify phenotypes as it learns to recognize clinical features invisible for humans. Here we apply ML to data from the huge European Narcolepsy Network (EU-NN) that contains hundreds of mixed features of narcolepsy making it difficult to analyze with classical statistics. Stochastic gradient boosting, a supervised learning model with built-in feature selection, results in high performances in testing set. While cataplexy features are recognized as the most influential predictors, machine find additional features, e.g. mean rapid-eye-movement sleep latency of multiple sleep latency test contributes to classify NT1 and NT2 as confirmed by classical statistical analysis. Our results suggest ML can identify features of CH on machine scale from complex databases, thus providing 'ideas' and promising candidates for future diagnostic classifications.

Idiopathic Hypersomnia

Idiopathic hypersomnia (IH) is a chronic neurologic disorder of daytime sleepiness, accompanied by long sleep times, unrefreshing sleep, difficulty in awakening, cognitive dysfunction, and autonomic symptoms. The cause is unknown; a genetic predisposition is suggested. Autonomic, inflammatory, or immune dysfunction has been proposed. Diagnosis involves a clinical history and objective testing. There are no approved treatments for IH, but modafinil is typically considered first-line. A substantial fraction of patients with IH are refractory or intolerant to standard treatments, and different treatment strategies using novel therapeutics are necessary. Even with current treatment options, quality of life and safety may remain impaired.

What Does One Sleep-Onset REM Period—During Either Nocturnal Polysomnography or Multiple Sleep Latency Test—Mean in Differential Diagnosis of Central Hypersomnias?

PURPOSE

The differentiation of narcolepsy without cataplexy from idiopathic hypersomnia is based on the number of sleep-onset rapid eye movement periods (SOREMPs) observed by multiple sleep latency test (MSLT) and nocturnal polysomnography. The main aim of this study was to investigate the utility of SOREMP in differential diagnosis of central hypersomnias.

METHODS

The authors retrospectively evaluated consecutive 101 patients with a normal polysomnography other than the presence of SOREMP and/or REM without atonia and a latency of ≤8 minutes in MSLT.

RESULTS

The authors classified patients as follows: 52 patients had at least 2 SOREMPs (narcolepsy group), 23 had no SOREMPs (idiopathic hypersomnia group), and 26 patients had only 1 SOREMP (intermediate group). In polysomnographic recordings, both mean sleep latency and REM latency were significantly shorter in the narcolepsy (P = 0.012, P < 0.001, respectively) and intermediate groups (P = 0.005 and P = 0.035, respectively) compared with the idiopathic hypersomnia group. In MSLT recordings, sleep latency was 2.7 ± 2.2 minutes in the narcolepsy group, 3.6 ± 1.4 minutes in the intermediate group, and 5.2 ± 2.7 minutes in the idiopathic hypersomnia group (P < 0.001). The mean REM latency and sleep stages SOREMPs arised from were similar between the narcolepsy and intermediate groups.

CONCLUSIONS

To date, SOREMPs in MSLT and polysomnography remain the sole electrodiagnostic feature that discriminates narcolepsy without cataplexy from idiopathic hypersomnia. Different parameters or combined criteria are being increasingly investigated to increase the sensitivity and specificity of MSLT. The findings showed an altered instability of REM sleep not only in patients with 2 or more SOREMPs in MSLT but also in patients with one SOREMP.

Hypocretin-1 Levels Associate with Fragmented Sleep in Patients with Narcolepsy Type 1

STUDY OBJECTIVES

We aimed to analyze nocturnal sleep characteristics of patients with narcolepsy type 1 (narcolepsy with cataplexy) measured by actigraphy in respect to cerebrospinal fluid hypocretin-1 levels of the same patients.

METHODS

Actigraphy recording of 1-2 w and hypocretin-1 concentration analysis were done to thirty-six unmedicated patients, aged 7 to 63 y, 50% female. Twenty-six of them had hypocretin-1 levels under 30 pg/mL and the rest had levels of 31-79 pg/mL.

RESULTS

According to actigraphy, patients with very low hypocretin levels had statistically significantly longer sleep latency (P = 0.033) and more fragmented sleep, indicated by both the number of immobile phases of 1 min (P = 0.020) and movement + fragmentation index (P = 0.049). There were no statistically significant differences in the actual sleep time or circadian rhythm parameters measured by actigraphy.

CONCLUSIONS

Actigraphy gives additional information about the stabilization of sleep in patients with narcolepsy type 1. Very low hypocretin levels associate with more wake intruding into sleep.

Central Disorders of Hypersomnolence: Focus on the Narcolepsies and Idiopathic Hypersomnia

The central disorders of hypersomnolence are characterized by severe daytime sleepiness, which is present despite normal quality and timing of nocturnal sleep. Recent reclassification distinguishes three main subtypes: narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia (IH), which are the focus of this review. Narcolepsy type 1 results from loss of hypothalamic hypocretin neurons, while the pathophysiology underlying narcolepsy type 2 and IH remains to be fully elucidated. Treatment of all three disorders focuses on the management of sleepiness, with additional treatment of cataplexy in those patients with narcolepsy type 1. Sleepiness can be treated with modafinil/armodafinil or sympathomimetic CNS stimulants, which have been shown to be beneficial in randomized controlled trials of narcolepsy and, quite recently, IH. In those patients with narcolepsy type 1, sodium oxybate is effective for the treatment of both sleepiness and cataplexy. Despite these treatments, there remains a subset of hypersomnolent patients with persistent sleepiness, in whom alternate therapies are needed. Emerging treatments for sleepiness include histamine H3 antagonists (eg, pitolisant) and possibly negative allosteric modulators of the gamma-aminobutyric acid-A receptor (eg, clarithromycin and flumazenil).

Polysomnographic Assessment of Sleep Comorbidities in Drug-Naïve Narcolepsy-Spectrum Disorders--A Japanese Cross-Sectional Study

This is a large cross-sectional study which aimed to investigate comorbidity rate, degree of sleep-related breathing disorder, polysomnigraphically diagnosible rapid eye movement sleep behavior disorder/rapid eye movement sleep without atonia and periodic limb movements during sleep in Japanese drug-naïve patients with narcolepsy-spectrum disorders. A total of 158 consecutive drug naïve patients with narcolepsy with cataplexy, 295 patients with narcolepsy without cataplexy and 395 patients with idiopathic hypersomnia without long sleep time were enrolled. From retrospectively analyzed data of nocturnal polysomnography and multiple sleep latency test, higher rates of periodic limb movements during sleep (> = 15 h^-1) (10.2%) and polysomnographically diagnosable rapid eye movement sleep behavior disorder (1.9%) were found in patients with narcolepsy with cataplexy. They had more severe periodic limb movements during sleep especially during rapid eye movement sleep and higher percentages of rapid eye movement sleep without atonia than the other two patient groups. In the present large sample study, Japanese drug naïve patients with narcolepsy with cataplexy showed the highest comorbidity rates of periodic limb movements during sleep, polysomnographically diagnosable rapid eye movement sleep behavior disorder and rapid eye movement sleep without atonia among those with the other narcolepsy-spectrum disorders; the rates were lower than those for Western patients.

Differences in electroencephalographic findings among categories of narcolepsy-spectrum disorders

OBJECTIVE

To clarify the differences in quantitative electroencephalographic (EEG) measures and their relation to clinical symptoms among narcolepsy-spectrum disorders.

METHODS

The enrolled patients were: 28 with narcolepsy with cataplexy (NA-CA); 16 with NA without cataplexy (NA w/o CA) and HLA-DRB1*1501/DQB1*0602 positive (NA w/o CA HLA+); 22 with NA w/o CA and HLA negative (NA w/o CA HLA-); and 22 with idiopathic hypersomnia without long sleep time (IHS w/o LST). Nocturnal polysomnography (n-PSG) and quantitative EEG evaluation, as well as the Multiple Sleep Latency test (MSLT), were conducted for all patients.

RESULTS

Patients with NA-CA or NA w/o CA HLA+ showed lower alpha power, higher delta and theta power during wakefulness, and higher alpha and beta power during rapid eye movement (REM) sleep, compared to those with NA w/o CA HLA- or IHS w/o LST. The former two groups also showed lower sleep efficiency and a higher rate of positivity of REM-related symptoms than the other two groups.

CONCLUSIONS

In narcolepsy, the presence of cataplexy and HLA positivity are associated with EEG slowing during wakefulness and increased fast EEG activity during REM sleep, REM-related symptoms and disrupted nocturnal sleep in narcolepsy.

Polysomnographic and actigraphic characteristics of patients with H1N1-vaccine-related and sporadic narcolepsy

OBJECTIVE

After the pandemic H1N1 influenza ASO3-adjuvanted vaccine, Pandemrix©, was used in late 2009 and early 2010, the incidence of narcolepsy increased in many European countries. This incidence mainly increased in children and adolescents and, to a lesser degree, in adults.

PATIENTS/METHODS

125 unmedicated patients, aged 4 to 61 years, were included in this case-series study. Of these, 69 were diagnosed to have an H1N1-vaccine-related narcolepsy and 57 had sporadic narcolepsy. Most of these patients had: an actigraphy recording of 1-2 weeks, polysomnography, a Multiple Sleep Latency Test (MSLT), and cerebrospinal fluid hypocretin-1 concentration analysis.

RESULTS

Patients with H1N1-vaccine-related narcolepsy had shorter diagnostic delays, lower periodic leg movement index during sleep, earlier sleep-wake rhythm, and were younger in age at diagnosis, compared with sporadic cases. They also had shorter sleep latency and more sleep onset REM periods in MSLT, but these results were strongly age-dependent. Actigraphy showed quantitatively less sleep and more sleep fragmentation than polysomnography.

CONCLUSION

Regarding polysomnographic and actigraphic characteristics, there were no dramatic deviations between H1N1-vaccine-related and sporadic narcolepsy. Circadian rhythms indicated some interesting new findings with respect to the H1N1-vaccine-related disease. An actigraphy recording of 1-2 weeks is useful when studying the nocturnal aspects of narcolepsy and sleep-wake rhythms of narcoleptic patients.

The hypocretin/orexin system: an increasingly important role in neuropsychiatry

Hypocretins, also named as orexins, are excitatory neuropeptides secreted by neurons specifically located in lateral hypothalamus and perifornical areas. Orexinergic fibers are extensively distributed in various brain regions and involved in a number of physiological functions, such as arousal, cognition, stress, appetite, and metabolism. Arousal is the most important function of orexin system as dysfunction of orexin signaling leads to narcolepsy. In addition to narcolepsy, orexin dysfunction is associated with serious neural disorders, including addiction, depression, and anxiety. However, some results linking orexin with these disorders are still contradictory, which may result from differences of detection methods or the precision of tools used in measurements; strategies targeted to orexin system (e.g., antagonists to orexin receptors, gene delivery, and cell transplantation) are promising new tools for treatment of neuropsychiatric disorders, though studies are still in a stage of preclinical or clinical research.

Challenges in diagnosing narcolepsy without cataplexy: a consensus statement

BACKGROUND

Diagnosing narcolepsy without cataplexy is often a challenge as the symptoms are nonspecific, current diagnostic tests are limited, and there are no useful biomarkers. In this report, we review the clinical and physiological aspects of narcolepsy without cataplexy, the limitations of available diagnostic procedures, and the differential diagnoses, and we propose an approach for more accurate diagnosis of narcolepsy without cataplexy.

METHODS

A group of clinician-scientists experienced in narcolepsy reviewed the literature and convened to discuss current diagnostic tools, and to map out directions for research that should lead to a better understanding and more accurate diagnosis of narcolepsy without cataplexy.

RECOMMENDATIONS

To aid in the identification of narcolepsy without cataplexy, we review key indicators of narcolepsy and present a diagnostic algorithm. A detailed clinical history is mainly helpful to rule out other possible causes of chronic sleepiness. The multiple sleep latency test remains the most important measure, and prior sleep deprivation, shift work, or circadian disorders should be excluded by actigraphy or sleep logs. A short REM sleep latency (≤ 15 minutes) on polysomnography can aid in the diagnosis of narcolepsy without cataplexy, although sensitivity is low. Finally, measurement of hypocretin levels can helpful, as levels are low to intermediate in 10% to 30% of narcolepsy without cataplexy patients.

Differences in brain morphological findings between narcolepsy with and without cataplexy

Objective

Maps of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) obtained by diffusion tensor imaging (DTI) can detect microscopic axonal changes by estimating the diffusivity of water molecules using magnetic resonance imaging (MRI). We applied an MRI voxel-based statistical approach to FA and ADC maps to evaluate microstructural abnormalities in the brain in narcolepsy and to investigate differences between patients having narcolepsy with and without cataplexy.

Methods

Twelve patients with drug-naive narcolepsy with cataplexy (NA/CA), 12 with drug-naive narcolepsy without cataplexy (NA w/o CA) and 12 age-matched healthy normal controls (NC) were enrolled. FA and ADC maps for these 3 groups were statistically compared by using voxel-based one-way ANOVA. In addition, we investigated the correlation between FA and ADC values and clinical variables in the patient groups.

Results

Compared to the NC group, the NA/CA group showed higher ADC values in the left inferior frontal gyrus and left amygdala, and a lower ADC value in the left postcentral gyrus. The ADC value in the right inferior frontal gyrus and FA value in the right precuneus were higher for NA/CA group than for the NA w/o CA group. However, no significant differences were observed in FA and ADC values between the NA w/o CA and NC groups in any of the areas investigated. In addition, no correlation was found between the clinical variables and ADC and FA values of any brain areas in these patient groups.

Conclusions

Several microstructural changes were noted in the inferior frontal gyrus and amygdala in the NA/CA but not in the NA w/o CA group. These findings suggest that these 2 narcolepsy conditions have different pathological mechanisms: narcolepsy without cataplexy form appears to be a potentially broader condition without any significant brain imaging differences from normal controls.

Disrupted nighttime sleep in narcolepsy

STUDY OBJECTIVES

Characterize disrupted nighttime sleep (DNS) in narcolepsy, an important symptom of narcolepsy.

METHODS

A panel of international narcolepsy experts was convened in 2011 to build a consensus characterization of DNS in patients with narcolepsy. A literature search of the Medline (1965 to date), Medline In-Process (latest weeks), Embase (1974 to date), Embase Alert (latest 8 weeks), and Biosis (1965 to date) databases was conducted using the following search terms: narcolepsy and disrupted nighttime sleep, disturbed nighttime sleep, fragmented sleep, consolidated sleep, sleep disruption, and narcolepsy questionnaire. The purpose of the literature search was to identify publications characterizing the nighttime sleep of patients with narcolepsy. The panel reviewed the literature. Nocturnal sleep can also be disturbed by REM sleep abnormalities such as vivid dreaming and REM sleep behavior disorder; however, these were not reviewed in the current paper, as we were evaluating for idiopathic sleep disturbances.

RESULTS

The literature reviewed provide a consistent characterization of nighttime sleep in patients with narcolepsy as fragmented, with reports of frequent, brief nightly awakenings with difficulties returning to sleep and associated reports of poor sleep quality. Polysomnographic studies consistently report frequent awakenings/arousals after sleep onset, more stage 1 (S1) sleep, and more frequent shifts to S1 sleep or wake from deeper stages of sleep. The consensus of the International Experts' Panel on Narcolepsy was that DNS can be distressing for patients with narcolepsy and that treatment of DNS warrants consideration.

CONCLUSIONS

Clinicians involved in the management of patients with narcolepsy should investigate patients' quality of nighttime sleep, give weight and consideration to patient reports of nighttime sleep experience, and consider DNS a target for treatment.