The role of cerebrospinal fluid hypocretin measurement in the diagnosis of narcolepsy and other hypersomnias

Living with Narcolepsy: Current Management Strategies, Future Prospects, and Overlooked Real-Life Concerns

Narcolepsy is a neurological disorder of the sleep-wake cycle characterized by excessive daytime sleepiness (EDS), cataplexy, nighttime sleep disturbances, and REM-sleep-related phenomena (sleep paralysis, hallucinations) that intrude into wakefulness. Dysfunction of the hypocretin/orexin system has been implicated as the underlying cause of narcolepsy with cataplexy. In most people with narcolepsy, symptom onset occurs between the ages of 10 and 35 years, but because the disorder is underrecognized and testing is complex, delays in diagnosis and treatment are common. Narcolepsy is treated with a combination of lifestyle modifications and medications that promote wakefulness and suppress cataplexy. Treatments are often effective in improving daytime functioning for individuals with narcolepsy, but side effects and/or lack of efficacy can result in suboptimal management of symptoms and, in many cases, significant residual impairment. Additionally, the psychosocial ramifications of narcolepsy are often neglected. Recently two new pharmacologic treatment options, solriamfetol and pitolisant, have been approved for adults, and the indication for sodium oxybate in narcolepsy has been expanded to include children. In recent years, there has been an uptick in patient-centered research, and promising new diagnostic and therapeutic options are in development. This paper summarizes current and prospective pharmacological therapies for treating both EDS and cataplexy, discusses concerns specific to children and reproductive-age women with narcolepsy, and reviews the negative impact of health-related stigma and efforts to address narcolepsy stigma.

Neurophysiology and Treatment of Disorders of Consciousness Induced by Traumatic Brain Injury: Orexin Signaling as a Potential Therapeutic Target

BACKGROUND

Traumatic brain injury (TBI) can cause disorders of consciousness (DOC) by impairing the neuronal circuits of the ascending reticular activating system (ARAS) structures, including the hypothalamus, which are responsible for the maintenance of the wakefulness and awareness. However, the effectiveness of drugs targeting ARAS activation is still inadequate, and novel therapeutic modalities are urgently needed.

METHODS

The goal of this work is to describe the neural loops of wakefulness, and explain how these elements participate in DOC, with emphasis on the identification of potential new therapeutic options for DOC induced by TBI.

RESULTS

Hypothalamus has been identified as a sleep/wake center, and its anterior and posterior regions have diverse roles in the regulation of the sleep/wake function. In particular, the posterior hypothalamus (PH) possesses several types of neurons, including the orexin neurons in the lateral hypothalamus (LH) with widespread projections to other wakefulness-related regions of the brain. Orexins have been known to affect feeding and appetite, and recently their profound effect on sleep disorders and DOC has been identified. Orexin antagonists are used for the treatment of insomnia, and orexin agonists can be used for narcolepsy. Additionally, several studies demonstrated that the agonists of orexin might be effective in the treatment of DOC, providing novel therapeutic opportunities in this field.

CONCLUSION

The hypothalamic-centered orexin has been adopted as the point of entry into the system of consciousness control, and modulators of orexin signaling opened several therapeutic opportunities for the treatment of DOC.

The Sustained Attention to Response Task Shows Lower Cingulo-Opercular and Frontoparietal Activity in People with Narcolepsy Type 1: An fMRI Study on the Neural Regulation of Attention

Vigilance complaints often occur in people with narcolepsy type 1 and severely impair effective daytime functioning. We tested the feasibility of a three-level sustained attention to response task (SART) paradigm within a magnetic resonance imaging (MRI) environment to understand brain architecture underlying vigilance regulation in individuals with narcolepsy type 1. Twelve medication-free people with narcolepsy type 1 and 11 matched controls were included. The SART included four repetitions of a baseline block and two difficulty levels requiring moderate and high vigilance. Outcome measures were between and within-group performance indices on error rates and reaction times, and functional MRI (fMRI) parameters: mean activity during the task and between-group activity differences across the three conditions and related to changes in activation over time (time-on-task) and error-related activity. Patients—but not controls—made significantly more mistakes with increasing difficulty. The modified SART is a feasible MRI vigilance task showing similar task-positive brain activity in both groups within the cingulo-opercular, frontoparietal, arousal, motor, and visual networks. During blocks of higher vigilance demand, patients had significantly lower activation in these regions than controls. Patients had lower error-related activity in the left pre- and postcentral gyrus. The time-on-task activity differences between groups suggest that those with narcolepsy are insufficiently capable of activating attention- and arousal-related regions when transitioning from attention initiation to stable attention, specifically when vigilance demand is high. They also show lower inhibitory motor activity in relation to errors, suggesting impaired executive functioning.

Health-related quality of life in patients with narcolepsy types 1 and 2 from a Sleep Center in Brazil

INTRODUCTION

Narcolepsy patients have higher prevalence of comorbidities, such as obesity, depression, and pain. Narcolepsy symptoms and concomitant medical conditions can impact the daily activities of patients. The objective of this study is to describe the quality of life in a sample of patients with narcolepsy, and the influence of the nutritional status in health domains.

METHODS

At Unifesp, two groups of 33 patients (narcolepsy types 1 and 2 meeting 2014 criteria, concerning hypocretin-1) and 33 controls without sleepiness, matched by age and sex, filled out the SF-36.

RESULTS

Narcolepsy groups, regardless of their nutritional status, had significantly lower scores in all domains, compared to controls, mainly in Role-physical, Role-emotional, and Energy/Fatigue. Role-physical score was lower in type 1 than in type 2 and controls (37.8±1.0 vs. 50.0±1.2 vs. 85.6±1.6; p<0.0001). Obese with type 2 narcolepsy scored lower than type 1 in physical scales.

CONCLUSION

In a Sleep Center in São Paulo, Brazil, physical and mental health were impaired in narcolepsy types 1 and 2. The first report of the poor health status in Brazilians with narcolepsy type 2 suggests that obesity negatively affects physical domains.

Involvement of orexinergic system in psychiatric and neurodegenerative disorders: A scoping review

Orexin is a neuropeptide secreted from lateral hypothalamus and pre-frontal cortex concerned in the wakefulness and excitement. This study aimed to review the possible neurobiological effect of orexin. A diversity of search strategies was adopted and assumed which included electronic database searches of Medline and PubMed using MeSH terms, keywords, and title words during the search. Orexin plays a vital role in activation of learning, memory acquisition, and consolidation through activation of monoaminergic system, which affect cognitive flexibility and cognitive function. Orexin stimulates adrenocorticotropin and corticosteroid secretions via activation of central corticotropin-releasing hormone. Cerebrospinal fluid (CSF) and serum orexin serum levels are reduced in depression, schizophrenia, and narcolepsy. However, high orexin serum levels are revealed in drug addictions. Regarding neurodegenerative brain diseases, CSF and serum orexin serum levels are reduced Parkinson disease, Alzheimer dementia, Huntington's disease, amyotrphic lateral sclerosis, and multiple sclerosis. Orexin antagonist leads to significant reduction of sympathetic over-activity during withdrawal syndrome. As well, orexin antagonist improves sleep pattern. Orexinergic system is involved in the different psychiatric and neurological disorders; therefore, targeting of this system could be possible novel pathway in the management of these disorders. In addition, measurement of CSF and serum orexin levels might predict the relapse and withdrawal of addict patients.

The influence of narcolepsy on olfactory function: a review

INTRODUCTION

Narcolepsy is a sleep disorder associated with loss of hypocretin cells characterized by irrepressible need to sleep, often accompanied by cataplexy, sleep fragmentation, hypnagogical and hypnopompic hallucinations, and sleep paralysis. It is also correlated with alterations in the sleep-wake cycle, dysautonomia, olfactory dysfunction, and eating disorders.

METHODS

This is a review about influence of narcolepsy on human olfaction. Pubmed, Embase, Ovid and Cochrane databases were searched for articles on the evaluation of olfactory function in narcoleptic patients including terms as narcolepsy, olfaction disorder, amongst others.

RESULTS

Seven articles met the inclusion criteria. In five of them, the olfaction of narcoleptic patients was diminished in comparison with healthy control groups. The diagnosis of narcolepsy relates to worse performance in olfactory tests. Experimental researches showed that hypocretin and hypocretin receptors are present in the olfactory system, and this neuropeptide may have a role on olfactory sensitivity and on the olfactory modulation. The cause of hyposmia appears to be multifactorial. Among them, it stands out the hypocretin deficiency, therefore, that seems to be involved in the olfactory impairment in narcoleptic patients.

Loss of Snord116 impacts lateral hypothalamus, sleep, and food-related behaviors

Imprinted genes are highly expressed in the hypothalamus; however, whether specific imprinted genes affect hypothalamic neuromodulators and their functions is unknown. It has been suggested that Prader-Willi syndrome (PWS), a neurodevelopmental disorder caused by lack of paternal expression at chromosome 15q11-q13, is characterized by hypothalamic insufficiency. Here, we investigate the role of the paternally expressed Snord116 gene within the context of sleep and metabolic abnormalities of PWS, and we report a significant role of this imprinted gene in the function and organization of the 2 main neuromodulatory systems of the lateral hypothalamus (LH) - namely, the orexin (OX) and melanin concentrating hormone (MCH) - systems. We observed that the dynamics between neuronal discharge in the LH and the sleep-wake states of mice with paternal deletion of Snord116 (PWScrm+/p-) are compromised. This abnormal state-dependent neuronal activity is paralleled by a significant reduction in OX neurons in the LH of mutant mice. Therefore, we propose that an imbalance between OX- and MCH-expressing neurons in the LH of mutant mice reflects a series of deficits manifested in the PWS, such as dysregulation of rapid eye movement (REM) sleep, food intake, and temperature control.

Pharmacologic Management of Excessive Daytime Sleepiness

Excessive daytime sleepiness (EDS) is related to medical and social problems, including mental disorders, physical diseases, poor quality of life, and so forth. According to the International Classification of Sleep Disorders, Third Edition, diseases that result from EDS are narcolepsy type 1, narcolepsy type 2, idiopathic hypersomnia, hypersomnia due to a medical disorder, and others. EDS is usually treated using amphetamine-like central nervous system stimulants or modafinil and its R-enantiomer, armodafinil, wake-promoting compounds unrelated to amphetamines; a variety of new drugs are under development. The side effects of some stimulants are potent and careful selection and management are required.

Blackout of my nights: Contentless, timeless and selfless report from the night in patients with central hypersomnias

At the extreme spectrum of consciousness during sleep, some patients with rare hypersomnias reported experiencing a specific night 'blackout' when sleeping, i.e., an absence of experiences or recall of them from sleep onset to offset. Thus, we explored through questionnaires the conscious experiences (dreaming experience, mind, self) during the night in 133 patients with idiopathic hypersomnia, 108 patients with narcolepsy, and 128 healthy controls. The night blackout was more frequent in idiopathic hypersomnia than in narcolepsy and control groups. Patients with idiopathic hypersomnia and frequent night amnesia had lower dream recall frequencies, and felt more often sleep as deep and mind as blank during the night. They had a higher proportion of slow wave sleep on their (retrospectively collected) sleep recordings than those without night blackout. This night blackout provides a new model for studying loss of consciousness during sleep, here as a contentless, selfless and timeless feeling upon awakening.

Sensitivity to gene dosage and gene expression affects genes with copy number variants observed among neuropsychiatric diseases

BACKGROUND

Copy number variants (CNVs) have been reported to be associated with diseases, traits, and evolution. However, it is hard to determine which gene should have priority as a target for further functional experiments if a CNV is rare or a singleton. In this study, we attempted to overcome this issue by using two approaches: by assessing the influences of gene dosage sensitivity and gene expression sensitivity. Dosage sensitive genes derived from two-round whole-genome duplication in previous studies. In addition, we proposed a cross-sectional omics approach that utilizes open data from GTEx to assess the effect of whole-genome CNVs on gene expression.

METHODS

Affymetrix Genome-Wide SNP Array 6.0 was used to detect CNVs by PennCNV and CNV Workshop. After quality controls for population stratification, family relationship and CNV detection, 287 patients with narcolepsy, 133 patients with essential hypersomnia, 380 patients with panic disorders, 164 patients with autism, 784 patients with Alzheimer disease and 1280 healthy individuals remained for the enrichment analysis.

RESULTS

Overall, significant enrichment of dosage sensitive genes was found across patients with narcolepsy, panic disorders and autism. Particularly, significant enrichment of dosage-sensitive genes in duplications was observed across all diseases except for Alzheimer disease. For deletions, less or no enrichment of dosage-sensitive genes with deletions was seen in the patients when compared to the healthy individuals. Interestingly, significant enrichments of genes with expression sensitivity in brain were observed in patients with panic disorder and autism. While duplications presented a higher burden, deletions did not cause significant differences when compared to the healthy individuals. When we assess the effect of sensitivity to genome dosage and gene expression at the same time, the highest ratio of enrichment was observed in the group including dosage-sensitive genes and genes with expression sensitivity only in brain. In addition, shared CNV regions among the five neuropsychiatric diseases were also investigated.

CONCLUSIONS

This study contributed the evidence that dosage-sensitive genes are associated with CNVs among neuropsychiatric diseases. In addition, we utilized open data from GTEx to assess the effect of whole-genome CNVs on gene expression. We also investigated shared CNV region among neuropsychiatric diseases.

Sleep Disorders in Four Patients With Myotonic Dystrophy Type 1

Sleep disturbances such as excessive daytime sleepiness, central and obstructive sleep apneas, restless legs syndrome, and rapid eye movement sleep dysregulation are prominent in patients with myotonic dystrophy type 1 (DM1). Mild intellectual deficits presented in many patients with DM1. In addition, psychosocial issues caused by neuropsychiatric symptoms are a clinical problem. We herein present the cases of four DM1 patients with sleep disturbances and neuropsychiatric symptoms in the preceding stage of clinically significant muscle symptoms. One of the cases exhibited a sleep disorder and neuropsychiatric symptoms before electromyography showed myotonic discharge, suggesting that careful follow-up is also important. Patients 1 and 2 were first referred to our department due to daytime sleepiness. Patients 3 and 4 were objectively suffering from daytime sleepiness of which they were not subjectively aware of. Patients 1, 3, and 4 obtained high apnea–hypopnea index (AHI) scores, which reflected central and/or obstructive apnea, whereas patient 2 had an AHI score of zero. The daytime cerebrospinal fluid (CSF) orexin levels of all patients ranged from the normal lower limit to low, although they were not as low as those observed in narcolepsy with typical cataplexy. Neuropsychological tests of patients 1 and 2 showed frontal lobe dysfunction. Patients 3 and 4 were diagnosed with mild intellectual disability and autism spectrum disorder, respectively. All patients exhibited indifference toward their own symptoms, which may have resulted from the cognitive decline caused by DM1. Based on family history and/or neurological findings such as myotonia, we suspected DM1 as the cause of their sleep disturbances. Molecular analysis using the triplet repeat-primed polymerase chain reaction (TP PCR) method and Southern blotting, which provided a genetic confirmation of the diagnosis of DM1, were performed. These clinical features of sleep disturbances were unrelated to the length of CTG repeats and are caused by unknown molecular mechanisms. Clinicians should take into account that multisystem involvement in DM1 is hugely variable, and thus, a disabling sleep disorder could overshadow muscle impairment in DM1 patients.

Neuroimaging of Narcolepsy and Primary Hypersomnias

Advances in neuroimaging open up the possibility for new powerful tools to be developed that potentially can be applied to clinical populations to improve the diagnosis of neurological disorders, including sleep disorders. At present, the diagnosis of narcolepsy and primary hypersomnias is largely limited to subjective assessments and objective measurements of behavior and sleep physiology. In this review, we focus on recent neuroimaging findings that provide insight into the neural basis of narcolepsy and the primary hypersomnias Kleine-Levin syndrome and idiopathic hypersomnia. We describe the role of neuroimaging in confirming previous genetic, neurochemical, and neurophysiological findings and highlight studies that permit a greater understanding of the symptoms of these sleep disorders. We conclude by considering some of the remaining challenges to overcome, the existing knowledge gaps, and the potential role for neuroimaging in understanding the pathogenesis and clinical features of narcolepsy and primary hypersomnias.

Antibody-Negative Paraneoplastic Limbic Encephalitis, Parkinsonism, Hypothermia, and Narcolepsy Associated with Endometrial Carcinoma

Background

We describe the clinical and neuropathological features of a patient with T-cell-mediated paraneoplastic limbic encephalitis, parkinsonism, hypothermia, and narcolepsy-like presentation associated with endometrial carcinoma.

Objectives

This patient with prominent parkinsonism and narcolepsy broadens the phenotype of known paraneoplastic syndromes and demonstrates the importance of investigation for occult malignancy even in the absence of paraneoplastic antibodies.

Methods

This is a case report with diagnosis confirmed at postmortem.

Results

Paraneoplastic antibodies were not detected. The initial improvement with immunosuppression was short lived, and postmortem neuropathological examination demonstrated encephalitis with predominant T-cell infiltration affecting the hypothalamus and extending to the brainstem, suggestive of a paraneoplastic syndrome.

Conclusions

Although the possibility of a novel antibody cannot be ruled out, consideration must also be given to recent demonstration of purely T-cell-mediated neuronal destruction in the context of paraneoplastic syndromes.

The Discovery of Suvorexant: Lessons Learned That Can Be Applied to Other CNS Drug Development Efforts

The development of therapeutics for central nervous system (CNS) disorders has many challenges that result in low probability of success and longer-than-typical development timelines. Suvorexant (Belsomra), the first dual orexin receptor antagonist used for insomnia, was approved by the United States Food and Drug Administration ∼10 years after the initial high-throughput screen was conducted to identify orexin receptor antagonists. What accounted for this success and speed? Here we suggest that this program was unique and set up for success by (1) having a robust and high-throughput pharmacodynamic readout that was translatable across species, including humans, (2) a well-validated target with a defined product profile, resulting in a highly energized team with a can-do attitude, and (3) a highly executable and streamlined clinical strategy. The utility of Belsomra for insomnia, as well as other neurological and psychiatric diseases, continues to be explored, most recently for insomnia associated with Alzheimer's disease.

Immunotherapy in Narcolepsy

PURPOSE OF REVIEW

Narcolepsy type 1 (NT1) is a chronic and disabling sleep disorder due to the loss of hypocretinergic neurons in the lateral hypothalamus pathophysiologically linked to an autoimmune process. Current treatment is symptomatic, and no cure is available to date. Immunotherapy is considered a promising future therapeutic option, and this review discusses the rationale for immunotherapy in narcolepsy, current evidences of its effects, outcome measures, and future directions.

RECENT FINDINGS

A limited number of case reports and uncontrolled small case series have reported the effect of different immunotherapies in patients with NT1. These studies were mainly based on the use of intravenous immunoglobulin (IVig), followed by corticosteroids, plasmapheresis, and monoclonal antibodies. Although initial reports showed an improvement of symptoms, particularly when patients were treated close to disease onset, other observations have not confirmed these results. Inadequate timing of treatment, placebo effects, and spontaneous improvement due to the natural disease course can account for these contrasting findings. Moreover, clear endpoints and standardized outcome measures have not been used and are currently missing in the pediatric population. On the basis of the available data, there are no enough evidences to support the use of immunotherapy in NT1. Randomized, controlled studies using clear endpoints and new outcome measures are needed to achieve a definitive answer about the usefulness of these treatments in narcolepsy.

Increased minimum alveolar concentration-awake of Sevoflurane in women of breast surgery with sleep disorders

BACKGROUND

Sleep disorders are commonly encountered in clinic. Evidences showed that sleep deprivation may modulate the effectiveness of general anesthetics in rats. However, this phenomenon has not been explored in humans. The study aimed to investigate whether the hypnotic potency of sevoflurane in patients with sleep disorders differ from patients with normal sleep habits.

METHODS

We recruited 44 patients scheduled for elective breast surgery and eventually analyzed 38 patients, including 19 subjects with normal sleep habits and 19 subjects with sleep disorders. According to the Dixon 'up-and-down' design, patients received sevoflurane at preselected concentrations starting at 1.0 vol%. After a steady-state period, a verbal command for testing awakening was performed. Based on the negative or positive response to the verbal command, we decreased or increased the concentration of sevoflurane by 0.2 vol% in the next patient accordingly. Plasma orexin-A was also measured before observation.

RESULTS

The MACawake of sevoflurane was 0.80% [95% confidence interval (CI), 0.683-0.926%] in the sleep disordered group vs 0.60% [95% CI, 0.493-0.689%] in the control group. The relative median potency between groups was 0.750 (95% CI, 0.236-0.969). Patients with sleep disorders had significantly higher orexin-A levels than control (72.17 ± 18.24 vs. 36.16 ± 14.18 pg/mL). A significant, positive relationship was detected between orexin-A level and probability of awakening (OR = 1.081, 95% CI is 1.020-1.146, P = 0.008).

CONCLUSIONS

MACawake of sevoflurane is higher in mild-aged women of breast surgery with sleep disorders compared to those with normal sleep habits. The increased anesthetic requirement may be related to changes of orexin-A levels. These findings suggest that sleep may have a potential impact on clinical anesthesia, including changes of sensitivity to anesthetics or postoperative complications. Further research is needed to confirm this hypothesis.

CLINICAL TRIAL REGISTRATION

Chinese Clinical Trial Registry (ChiCTR1800016022), date of registration 07 May 2018.

Knowledge Gaps in the Perioperative Management of Adults With Narcolepsy: A Call for Further Research

There is increasing awareness that sleep disorders may be associated with increased perioperative risk. The Society of Anesthesia and Sleep Medicine created the Narcolepsy Perioperative Task Force: (1) to investigate the current state of knowledge of the perioperative risk for patients with narcolepsy, (2) to determine the viability of developing perioperative guidelines for the management of patients with narcolepsy, and (3) to delineate future research goals and clinically relevant outcomes. The Narcolepsy Perioperative Task Force established that there is evidence for increased perioperative risk in patients with narcolepsy; however, this evidence is sparse and based on case reviews, case series, and retrospective reviews. Mechanistically, there are a number of potential mechanisms by which patients with narcolepsy could be at increased risk for perioperative complications. These include aggravation of the disease itself, dysautonomia, narcolepsy-related medications, anesthesia interactions, and withdrawal of narcolepsy-related medications. At this time, there is inadequate research to develop an expert consensus or guidelines for the perioperative management of patients with narcolepsy. The paucity of available literature highlights the critical need to determine if patients with narcolepsy are at an increased perioperative risk and to establish appropriate research protocols and clearly delineated patient-centered outcomes. There is a real need for collaborative research among sleep medicine specialists, surgeons, anesthesiologists, and perioperative providers. This future research will become the foundation for the development of guidelines, or at a minimum, a better understanding how to optimize the perioperative care of patients with narcolepsy.

Comorbidity of Narcolepsy and Psychotic Disorders: A Nationwide Population-Based Study in Taiwan

BACKGROUND

Narcolepsy is a chronic sleep disorder that is likely to have neuropsychiatric comorbidities. Psychotic disorders are characterized by delusion, hallucination, and reality impairments. This study investigates the relationship between narcolepsy and psychotic disorders.

DESIGN AND METHODS

This study involves patients who were diagnosed with narcolepsy between January 2002 and December 2011 (n = 258) and age- and gender-matched controls (n = 2580) from Taiwan's National Health Insurance database. Both the patients and the controls were monitored from January 1, 2002 to December 31, 2011 to identify any occurrence of a psychotic disorder. Drugs that have been approved for treating narcolepsy: immediate-release methylphenidate (IR-MPH), osmotic controlled-release formulations of methylphenidate (OROS-MPH), and modafinil, were analyzed. A multivariate logistic regression model was used to evaluate the potential comorbidity of narcolepsy with psychotic disorders.

RESULTS

During the study period, 8.1% of the narcoleptic patients exhibited comorbidity with a psychotic disorder, whereas only 1.5% of the control subjects (1.5%) had psychotic disorders (aOR, 4.07; 95% CI, 2.21-7.47). Of the narcolepsy patients, 41.5, 5.4, and 13.2% were treated with MPH-IR, MPH-OROS, and modafinil, accordingly. Pharmacotherapy for narcolepsy did not significantly affect the risk of exhibiting a psychotic disorder.

CONCLUSIONS

This nationwide study revealed that narcolepsy and psychotic disorders commonly co-occur. Pharmacotherapy for narcolepsy was not associated with the risk of psychotic disorders. Our findings serve as a reminder that clinicians must consider the comorbidity of narcolepsy and psychosis.

REM sleep behavior disorder in narcolepsy: A secondary form or an intrinsic feature?

Disrupted nighttime sleep is one of the pentad of symptoms defining Narcolepsy. REM sleep behavior disorder (RBD) largely contributes to night sleep disruption and narcolepsy is the most common cause of secondary RBD. However, RBD linked to narcolepsy (N-RBD) has been insufficiently characterized, leaving unsolved a number of issues. Indeed, it is still debated whether N-RBD is an intrinsic feature of narcolepsy, as indubitable for cataplexy, and therefore strictly linked to the cerebrospinal fluid hypocretin-1 (CSF hcrt-1) deficiency, or an associated feature, with a still unclear pathophysiology. The current review aims at rendering a comprehensive state-of-the-art of N-RBD, highlighting the open and unsettled topics. RBD reportedly affects 30-60% of patients with Narcolepsy type 1 (NT1), but it may be seen also in Narcolepsy type 2 (NT2). When compared to idiopathic/isolated RBD (iRBD), N-RBD has been reported to be characterized by less energetic and quieter episode, which however occur with the same probability in the first and the second part of the night and sometime even subcontinuously. N-RBD patients are generally younger than those with iRBD. N-RBD has been putatively linked to wake-sleep instability due to CSF hcrt-1 deficiency, but this latter by itself cannot explain completely the phenomenon as N-RBD has not been universally linked to low CSF hcrt-1 levels and it may be observed also in NT2. Therefore, other factors may probably play a role and further studies are needed to clarify this issue. In addition, therapeutic options have been poorly investigated.

[Narcolepsy: From the discovery of a wake promoting peptide to autoimmune T cell biology and molecular mimicry with flu epitopes]

Narcolepsy-cataplexy was first described in the late 19th century in Germany and France. Prevalence was established to be 0.05 % and a canine model was discovered in the 1970s. In 1983, a Japanese study found that all patients carried HLA-DR2, suggesting autoimmunity as the cause of the disease. Studies in the canine model established that dopaminergic stimulation underlies anti-narcoleptic action of psychostimulants, while antidepressants were found to suppress cataplexy through adrenergic reuptake inhibition. No HLA association was found in canines. A linkage study initiated in 1988 revealed in hypocretin (orexin) receptor two mutations as the cause of canine narcolepsy in 1999. In 1992, studies on African Americans showed that DQ0602 was a better marker than DR2 across all ethnic groups. In 2000, hypocretin-1/orexin A levels were measured in the cerebrospinal fluid (CSF) and found to be undetectable in most patients, establishing hypocretin deficiency as the cause of narcolepsy. Decreased CSF hypocretin-1 was then found to be secondary to the loss of the 70,000 neurons producing hypocretin in the hypothalamus, suggesting immune destruction of these cells as the cause of the disease. Additional genetic studies, notably genome wide associations (GWAS), found multiple genetic predisposing factors for narcolepsy. These were almost all involved in other autoimmune diseases, although a strong and unique association with T cell receptor (TCR) alpha and beta loci were observed. Nonetheless, all attempts to demonstrate presence of autoantibodies against hypocretin cells in narcolepsy failed, and the presumed autoimmune cause remained unproven. In 2009, association with strep throat infections were found, and narcolepsy onsets were found to occur more frequently in spring and summer, suggesting upper away infections as triggers. Following reports that narcolepsy cases were triggered by vaccinations and infections against influenza A 2009 pH1N1, a new pandemic strain that erupted in 2009, molecular mimicry with influenza A virus was suggested in 2010. This hypothesis was later confirmed by peptide screening showing higher activity of CD4⁺ T cell reactivity to a specific post-translationally amidated segment of hypocretin (HCRT-_NH2) and cross-reactivity of specific TCRs with a pH1N1-specific segment of hemagglutinin that shares homology with HCRT-_NH2. Strikingly, the most frequent TCR recognizing these antigens was found to carry sequences containing TRAJ24 or TRVB4-2, segments modulated by narcolepsy-associated genetic polymorphisms. Cross-reactive CD4⁺ T cells with these cross-reactive TCRs likely subsequently recruit CD8⁺ T cells that are then involved in hypocretin cell destruction. Additional flu mimics are also likely to be discovered since narcolepsy existed prior to 2009. The work that has been conducted over the years on narcolepsy offers a unique perspective on the conduct of research on the etiopathogeny of a specific disease.

Narcolepsy in Children and Adults: A Guide to Improved Recognition, Diagnosis and Management

Narcolepsy is a rare condition that affects children and adults, and commonly has an onset in childhood. Time to appropriate diagnosis frequently is at least a decade. Unrecognized or misdiagnosed symptoms of narcolepsy contribute to increased morbidity, disability and socioeconomic liability in these patients. Delays in diagnosis may be related to variability in presentation in childhood, lack of familiarity with symptoms or appropriate diagnostic testing or misdiagnosis with accidental introduction of treatment that may modify or mask narcolepsy features. Improved awareness about the diagnosis and tailored therapies improve clinical and socioeconomic outcomes by reducing time to effective treatment. Application of effective treatment results in long-term benefits by improving clinical outcomes, potentially enabling improved education, increased employment opportunity, and improved work productivity and quality of life. This review provides a comprehensive stepwise approach to improve knowledge and comfort for recognition of symptoms, diagnostic strategies and management considerations of narcolepsy in children and adults.

HLA and sleep parameter associations in post-H1N1 narcolepsy type 1 patients and first-degree relatives

Study Objectives

To explore HLA (human leukocyte antigen) in post-H1N1 narcolepsy type 1 patients (NT1), first-degree relatives and healthy controls, and assess HLA associations with clinical and sleep parameters in patients and first-degree relatives.

Methods

Ninety post-H1N1 NT1 patients and 202 of their first-degree relatives were HLA-genotyped (next generation sequencing) and phenotyped (semistructured interviews, Stanford Sleep Questionnaire, polysomnography, and multiple sleep latency test). HLA allele distributions were compared between DQB1*06:02-heterozygous individuals (77 patients, 59 parents, 1230 controls). A subsample (74 patients, 114 relatives) was investigated for associations between HLA-loci and continuous sleep variables using logistic regression. Identified candidate HLA-loci were explored for HLA allele associations with hypnagogic hallucinations and sleep paralysis in 90 patients, and patient allele findings were checked for similar associations in 202 relatives.

Results

DQB1*06:02 heterozygous post-H1N1 NT1 patients (84.4% H1N1-vaccinated) showed several significant HLA associations similar to those reported previously in samples of mainly sporadic NT1, i.e. DQB1*03:01, DRB1*04:01, DRB1*04:02, DRB1*04:07, DRB1*11:04, A*25:01, B*35:03, and B*51:01, and novel associations, i.e. B*14:02, C*01:02, and C*07:01. Parents HLA alleles did not deviate significantly from controls. The HLA-C locus was associated with sleep parameters in patients and relatives. In patients C*02:02 seems to be associated with protective effects against sleep paralysis and hypnagogic hallucinations.

Conclusions

Our findings of similar risk/protective HLA-alleles in post-H1N1 as in previous studies of mainly sporadic narcolepsy support similar disease mechanisms. We also report novel allelic associations. Associations between HLA-C and sleep parameters were seen independent of NT1 diagnosis, supporting involvement of HLA-C in sleep subphenotypes.

Growth Hormone Deficiency and Excessive Sleepiness: A Case Report and Review of the Literature

The somatotropic axis is intricately involved in normal sleep, as evidenced by the fact that hypothalamic growth hormone-releasing hormone (GHRH) has sleep promoting effects and pituitary growth hormone (GH) release is strongly associated with slow-wave sleep (SWS). Abnormalities in the somatotropic axis, such as GH deficiency of hypothalamic or pituitary origin, result in an alteration of normal sleep patterns which may explain the fatigue reported in these individuals. Sleep disorders such as narcolepsy, in which individuals abnormally enter rapid eye movement (REM) sleep at sleep onset are also associated with an altered GHRH circadian rhythm and abnormal GH secretion. While few studies are available, this review explores what is known about sleep abnormalities in GH deficiency, the effect of treatment on sleep in patients with GH deficiency, and GH secretion in narcolepsy. Emerging evidence suggests a hypothalamic link between narcolepsy and GH secretion. We also describe the unique constellation of isolated idiopathic GH deficiency and severe excessive sleepiness in adopted Nicaraguan siblings, one of which has narcolepsy and the other idiopathic hypersomnia.

Reduced plasma orexin-A levels in patients with bipolar disorder

PURPOSE

Orexins are hypothalamic neuropeptides involved in the regulation of sleep, appetite and arousal. An altered orexin system has been implicated in the pathophysiology of psychiatric disorders. This study aimed to examine whether plasma orexin-A levels differ in patients with schizophrenia, major depressive disorder (MDD), or bipolar disorder (BD) compared to in healthy controls. We also examined the possible correlations between plasma orexin-A levels and clinical variables.

PATIENTS AND METHODS

All participants were Japanese. The sample consisted of 80 patients with schizophrenia (42 women, 52.5%; mean age 36.8 years), 80 patients with MDD (43 women, 53.8%; 43.7 years), and 40 patients with BD (24 women, 60%; 41.1 years), as well as 80 healthy controls (48 women, 60%; 47.0 years). Plasma orexin-A levels were quantified by an enzyme-linked immunosorbent assay.

RESULTS

Mean orexin-A levels were significantly different across the four diagnostic groups (F=4.09; df=3; p=0.007, η2 =0.06). In particular, the patients with BD showed significantly lower orexin-A levels than did the controls. When the median value of the control group (109.8 pg/ml) was set as a cut-off value, subjects whose orexin-A levels were below the cut-off were more common in all psychiatric groups (schizophrenia: 73.8%, x2 =9.56, df=1, p=0.003, OR=2.81, 95% CI: 1.45 to 5.45, d=0.57; MDD: 78.5%, x2 =14.02, df=1, p<0.001, OR=3.65, 95% CI: 1.82 to 7.29, d=0.72; BD: 87.5%, x2 =16.0, df=1, p<0.001, OR=7.00, 95% CI: 2.49 to 19.70, d=1.07). We found no association between plasma orexin-A levels and any clinical symptoms, depression severity, or medication doses.

CONCLUSION

Our results suggest that plasma orexin-A levels are reduced in patients with BD.

Widespread white matter connectivity abnormalities in narcolepsy type 1: A diffusion tensor imaging study

Narcolepsy type 1 is caused by a selective loss of hypothalamic hypocretin-producing neurons, resulting in severely disturbed sleep-wake control and cataplexy. Hypocretin-producing neurons project widely throughout the brain, influencing different neural networks. We assessed the extent of microstructural white matter organization and brain-wide structural connectivity abnormalities in a homogeneous group of twelve drug-free patients with narcolepsy type 1 and eleven matched healthy controls using diffusion tensor imaging with multimodal analysis techniques. First, tract-based spatial statistics (TBSS) was carried out using fractional anisotropy (FA) and mean, axial and radial diffusivity (MD, AD, RD). Second, quantitative analyses of mean FA, MD, AD and RD were conducted in predefined regions-of-interest, including sleep-wake regulation-related, limbic and reward system areas. Third, we performed hypothalamus-seeded tractography towards the thalamus, amygdala and midbrain. TBSS analyses yielded brain-wide significantly lower FA and higher RD in patients. Localized significantly lower FA and higher RD in the left ventral diencephalon and lower AD in the midbrain, were seen in patients. Lower FA was also found in patients in left hypothalamic fibers connecting with the midbrain. No significant MD and AD differences nor a correlation with disease duration were found. The brain-wide, localized ventral diencephalon (comprising the hypothalamus and different sleep- and motor-related nuclei) and hypothalamic connectivity differences clearly show a heretofore underestimated direct and/or indirect effect of hypocretin deficiency on microstructural white matter composition, presumably resulting from a combination of lower axonal density, lower myelination and/or greater axon diameter.

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Patients with narcolepsy type 1 have brain-wide microstructural white matter disruptions.

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Patients have overall lower fractional anisotropy and higher radial diffusivity.

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Fractional anisotropy was most prominently lower in the left ventral diencephalon.

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Lower fractional anisotropy was seen in patients in tracts connecting the left hypothalamus with the midbrain.

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Patients suffer from a combination of lower axonal density, lower myelination and/or greater axon diameter.

Narcolepsy type 1

Although being the second most common cause of disabling daytime sleepiness in the world, narcolepsy in India is seldom diagnosed. So far, only two cases had been reported. This is the case of narcolepsy in a 15-year-old female student struggling in her scholastic pursuit because of the disease.

The neurophysiological basis of excessive daytime sleepiness: suggestions of an altered state of consciousness

Excessive daytime sleepiness (EDS) is characterized by difficulty staying awake during daytime, though additional features may be present. EDS is a significant problem for clinical and non-clinical populations, being associated with a range of negative outcomes that also represent a burden for society. Extreme EDS is associated with sleep disorders, most notably the central hypersomnias such as narcolepsy, Kleine-Levin syndrome, and idiopathic hypersomnia (IH). Although investigation of these conditions indicates that EDS results from diminished sleep quality, the underlying cause for this impairment remains uncertain. One possibility could be that previous research has been too narrow in scope with insufficient attention paid to non-sleep-related aspects. Here, we offer a broader perspective in which findings concerning the impact of EDS on cortical functioning are interpreted in relation to current understanding about the neural basis of consciousness. Alterations in the spatial distribution of cortical activity, in particular reduced connectivity of frontal cortex, suggest that EDS is associated with an altered state of consciousness.

The sensory pain of Dante's Inferno - Semantics of chronic pain in patients with narcolepsy

Objective

To examine the semantics of chronic pain in narcolepsy and to compare with the poem Inferno, from Dante Alighieri.

Methods

A cross-sectional study, in which type 1 (n=33) and type 2 (n=33) patients (hypocretin-1 quantification in cerebrospinal fluid), were studied at Departamento de Psicobiologia - Universidade Federal de São Paulo (Brazil). We assessed pain descriptors in the Present Rating Index (PRI) from McGill Pain Questionnaire.

Results

There was no significant difference in PRI between narcolepsy groups. In both groups, the most frequent words had a sensory dimension: throbbing, jumping, and tugging. Multiple correspondence analysis revealed the predominance of sensory descriptors and the deficiency of affective descriptors in these groups.

Discussion

A study that interpreted the poem Inferno, from Dante Alighieri, as McGill Pain Questionnaires descriptors suggested a contribution of the sensory dimension in pain of possibly narcolepsy patients, similar as in our results.

H1N1 hemagglutinin-specific HLA-DQ6-restricted CD4+ T cells can be readily detected in narcolepsy type 1 patients and healthy controls

Following the 2009 H1N1 influenza pandemic, an increased risk of narcolepsy type 1 was observed. Homology between an H1N1 hemagglutinin and two hypocretin sequences has been reported. T cell reactivity to these peptides was assessed in 81 narcolepsy type 1 patients and 19 HLA-DQ6-matched healthy controls. HLA-DQ6-restricted H1N1 hemagglutinin-specific T cell responses were detected in 28.4% of patients and 15.8% of controls. Despite structural homology between HLA-DQ6-hypocretin and -H1N1 peptide complexes, T cell cross-reactivity was not detected. These results indicate that it is unlikely that cross-reactivity between H1N1 hemagglutinin and hypocretin peptides presented by HLA-DQ6 is involved in the development of narcolepsy.

Management of Excessive Daytime Sleepiness in Narcolepsy With Baclofen

BACKGROUND

Narcolepsy is a disabling sleep-wake disorder characterized by the pentad symptoms of excessive daytime sleepiness, sleep paralysis, sleep fragmentation, sleep-related hallucinations, and cataplexy. There is no curative therapy for narcolepsy. Treatment is therefore symptom directed. Symptom management is generally directed at improving excessive daytime sleepiness, sleep fragmentation, and cataplexy. First-line treatment for excessive daytime sleepiness is typically daily use of wake-promoting agents, such as modafinil or armodafinil, or stimulant therapy, such as methylphenidate or amphetamines. Alternatively, sodium oxybate can be used nightly for improved cataplexy, sleep consolidation, and following day wakefulness. These therapies can be limited in some patients because of inadequate efficacy, poor tolerability, or side effects.

METHODS

We describe five narcolepsy patients with severe excessive daytime sleepiness who had an inadequate response or experienced side effects with the initial therapies but had a positive response to treatment with baclofen.

RESULTS

These patients reported subjective improvement in sleep maintenance without fragmentation and daytime sleepiness. Average Epworth Sleepiness Scale assessment before treatment was 15.8 with post-treatment assessment being 10.4 (P < 0.05).

CONCLUSIONS

Baclofen may be an effective treatment for excessive daytime sleepiness and sleep fragmentation in narcolepsy and warrants further study.

The Functional Role of Dreaming in Emotional Processes

Dream experience (DE) represents a fascinating condition linked to emotional processes and the human inner world. Although the overlap between REM sleep and dreaming has been overcome, several studies point out that emotional and perceptually vivid contents are more frequent when reported upon awakenings from this sleep stage. Actually, it is well-known that REM sleep plays a pivotal role in the processing of salient and emotional waking-life experiences, strongly contributing to the emotional memory consolidation. In this vein, we highlighted that, to some extent, neuroimaging studies showed that the processes that regulate dreaming and emotional salience in sleep mentation share similar neural substrates of those controlling emotions during wakefulness. Furthermore, the research on EEG correlates of the presence/absence of DE and the results on EEG pattern related to the incorporated memories converged to assign a crucial role of REM theta oscillations in emotional re-processing. In particular, the theta activity is involved in memory processes during REM sleep as well as during the waking state, in line with the continuity hypothesis. Also, the gamma activity seems to be related to emotional processes and dream recall as well as to lucid dreams. Interestingly, similar EEG correlates of DE have been found in clinical samples when nightmares or dreams occur. Research on clinical samples revealed that promoting the rehearsal of frightening contents aimed to change them is a promising method to treat nightmares, and that lucid dreams are associated with an attenuation of nightmares. In this view, DE can defuse emotional traumatic memories when the emotional regulation and the fear extinction mechanisms are compromised by traumatic and frightening events. Finally, dreams could represent a sort of simulation of reality, providing the possibility to create a new scenario with emotional mastery elements to cope with dysphoric items included in nightmares. In addition, it could be hypothesized that the insertion of bizarre items besides traumatic memories might be functional to "impoverish" the negative charge of the experiences.

Measurement of symptoms in idiopathic hypersomnia

Objective

To validate the Idiopathic Hypersomnia Severity Scale (IIHSS), a self-report measure of hypersomnolence symptoms, consequences, and responsiveness to treatment.

Methods

The 14-item IHSS (developed and validated by sleep experts with patients' feedback) was filled in by 218 participants (2.3% missing data). Among the 210 participants who fully completed the IHSS, there were 57 untreated and 43 treated patients with idiopathic hypersomnia (IH) aged 16 years or older, 37 untreated patients with narcolepsy type 1 (NT1), and 73 controls without sleepiness. IHSS psychometric properties, discriminant diagnostic validity, and score changes with treatment were assessed.

Results

The IHSS showed good internal consistency and content validity. Factor analysis indicated a 2-component solution with good reliability expressed by satisfactory Cronbach α values. IHSS scores were reproducible without changes in the test–retest evaluation (13 treated and 14 untreated patients). Convergent validity analysis showed that IHSS score was correlated with daytime sleepiness, depressive symptoms, and quality of life in patients with IH. The IHSS score was lower in treated than untreated patients (5–8 unit difference, without ceiling effect). The cutoff value for discriminating between untreated and treated patients was 26/50 (sensitivity 55.8%, specificity 78.9%). IHSS scores were higher in drug-free IH patients than NT1 and controls. The best cutoff value to differentiate between untreated IH patients and controls was 22 (sensitivity 91.1%, specificity 94.5%), and 29 with NT1.

Conclusions

The IHSS is a reliable and valid clinical tool for the quantification of IH symptoms and consequences that might be useful for patient identification, follow-up, and management.

The neurobiological basis of narcolepsy

Narcolepsy is the most common neurological cause of chronic sleepiness. The discovery about 20 years ago that narcolepsy is caused by selective loss of the neurons producing orexins (also known as hypocretins) sparked great advances in the field. Here, we review the current understanding of how orexin neurons regulate sleep-wake behaviour and the consequences of the loss of orexin neurons. We also summarize the developing evidence that narcolepsy is an autoimmune disorder that may be caused by a T cell-mediated attack on the orexin neurons and explain how these new perspectives can inform better therapeutic approaches.

HPLC analysis of CSF hypocretin-1 in type 1 and 2 narcolepsy

Narcolepsy is a chronic sleep disorder caused by a loss of hypocretin (hcrt) neurons in the hypothalamus. Cerebrospinal fluid (CSF) hcrt-1 measurement has been well established as a gold standard of narcolepsy diagnosis, although some portions of narcoleptic patients show normal hcrt-1 levels. We aimed to examine peptide degradation of hcrt-1 and its abnormality in the CSF of patients by using high performance liquid chromatography (HPLC) followed by radioimmunoassay (RIA). CSF was collected from healthy controls, narcoleptic patients of type 1 with hcrt-1 deficiency, type 1 with normal hcrt-1 level, and type 2 with normal hcrt-1 level. We found that the majority of hcrt-1 immunoreactivity in extracted CSF was derived from unauthentic hcrt-1 peaks, which are predicted to be inactive metabolites, and the intact hcrt-1 peptide was less than 10% of the gross amount, suggesting that the regular RIA for CSF hcrt-1 measures largely reflect the unauthentic hcrt-1-related metabolites rather than the intact one. As expected, all hcrt-1-related peaks were abolished in type 1 with hcrt-1 deficiency. Importantly, we also found that the sum of the authentic hcrt-1 peptide (peaks 3 and 4) significantly decreased in non-deficient type 1 and tended to decrease in type 2 narcoleptic patients although the levels with the regular RIA in non-extracted CSF was equivalent to healthy controls. Immunoreactivity with unauthentic hcrt-1 metabolites may masks the possible decline in authentic hcrt-1 level caused by the partial loss of hcrt neurons. Our findings may provide new insights into the degradation of the hcrt-1 peptide and the pathophysiology of narcolepsy.

Genetics of narcolepsy

Narcolepsy is a term that was initially coined by Gélineáu in 1880 and is a chronic neurological sleep disorder that manifests as a difficulty in maintaining wakefulness and sleep for long periods. Currently, narcolepsy is subdivided into two types according to the International Classification of Sleep Disorders, 3rd edition: narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2). NT1 is characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis and is caused by a marked reduction in neurons in the hypothalamus that produce orexin (hypocretin), which is a wakefulness-associated neuropeptide. Except for cataplexy, NT2 exhibits most of the same symptoms as NT1. NT1 is a multifactorial disease, and genetic variations at multiple loci are associated with NT1. Almost all patients with NT1 carry the specific human leukocyte antigen (HLA) allele HLA-DQB1 ^* 06:02. Genome-wide association studies have uncovered >10 genomic variations associated with NT1. Rare variants associated with NT1 have also been identified by DNA genome sequencing. NT2 is also a complex disorder, but its underlying genetic architecture is poorly understood. However, several studies have revealed loci that increase susceptibility to NT2. The currently identified loci cannot explain the heritability of narcolepsy (NT1 and NT2). We expect that future genomic research will provide important contributions to our understanding of the genetic basis and pathogenesis of narcolepsy.

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.

Management Of Excessive Sleepiness In Patients With Narcolepsy And OSA: Current Challenges And Future Prospects

Excessive daytime sleepiness (EDS) can be caused by insufficient sleep but is also a manifestation of medical or sleep disorders and a side effect of medications. It impacts quality of life and creates safety concerns in the home, at work, and on the roads. Screening questionnaires can be used to estimate EDS, but further evaluation is necessary. EDS is a common symptom of both narcolepsy and obstructive sleep apnea (OSA). Polysomnography and multiple sleep latency testing are used to diagnose these disorders. However, isolating the primary etiology of EDS can be challenging and may be multifactorial. Untreated OSA can show polysomnographic findings that are similar to narcolepsy. The effects of sleep deprivation and certain medications can also affect the polysomnographic results. These challenges can lead to misdiagnosis. In addition, narcolepsy and OSA can occur as comorbid disorders. If EDS persists despite adequate treatment for either disorder, a comorbid diagnosis should be sought. Thus, despite advances in clinical practice, appropriate management of these patients can be challenging. This review is focused on EDS due to OSA and narcolepsy and addresses some of the challenges with managing this patient population.

The neurophysiology of hyperarousal in restless legs syndrome: Hints for a role of glutamate/GABA

Restless legs syndrome (RLS) is a common sensory-motor circadian disorder, whose basic components include urge to move the legs, unpleasant sensory experience, and periodic leg movements during sleep, all associated with an enhancement of the individual's arousal state. Brain iron deficiency (BID) is considered to be a key initial pathobiological factor, based on alterations of iron acquisition by the brain, also moderated by genetic factors. In addition to the well-known dopaminergic involvement in RLS, previous studies pointed out that BID brings also a hyperglutamatergic state that influences a dysfunctional cortico-striatal-thalamic-cortical circuit in genetically vulnerable individuals. However, the enhancement of arousal mechanisms in RLS may also be explained by functional changes of the ascending arousal systems and by deficitary GABA-mediated inhibitory control. Very recently, it was also suggested that BID induces a hypoadenosinergic state in RLS, thus possibly providing a link for a putative unified pathophysiological mechanism accounting for both hyperarousal and sensory-motor signs. Consequently, RLS might be viewed as a multitransmitter neurochemical disorder, globally resulting in enhanced excitability and decreased inhibition. In this framework, understanding the complex interaction of different neuronal circuits in generating the symptoms of RLS is mandatory both for a better diagnostic refinement and for an innovative therapeutic support. Notably, multiple neurotransmission dysfunction, either primary or triggered by BID, may also bridge the gap between RLS and other chronic pain disorders. This chapter summarizes the current experimental and clinical findings into a heuristic model of the electrophysiology and neurochemistry underlying RLS.