Narcolepsy: clinical features, new pathophysiologic insights, and future perspectives

Nocturnal aspects of narcolepsy with cataplexy

Even though the most impressive manifestation of narcolepsy is excessive sleepiness, paradoxically a significant number of patients have trouble sleeping at night. A wide array of alterations can affect the night-time sleep of a narcoleptic patient, and the aim of this review is to increase awareness on this issue, thereby enhancing the care of narcoleptic patients by more specific approaches to their disturbed night sleep. This review covers a broad variety of nocturnal sleep features in narcolepsy. Starting from animal models and the clinical features of patients, the paper then discusses the many comorbid conditions found in narcolepsy at night, the most advanced methods of analysis and the few recent advances in the specific treatment of night sleep in narcoleptic patients.

Manipulation of core body and skin temperature improves vigilance and maintenance of wakefulness in narcolepsy

CONTEXT

Impaired vigilance and sleepiness are two majordaily complaints of patients with narcolepsy. We previously showed their sleepiness to be correlated to an abnormally regulated skin temperature, i.e., increased distal skin temperature compared with proximal skin temperature.

OBJECTIVE

Our goal was to investigate a possible causal contribution of skin temperature disturbances to impairments in the ability to maintain vigilance and wakefulness in narcolepsy.

DESIGN

In a modified constant routine protocol, the Psychomotor Vigilance Task (PVT) and the Maintenance of Wakefulness Test (MWT) were repeatedly assessed. Meanwhile, skin and core body temperatures were mildly manipulated within the thermoneutral range of the normal diurnal rhythm using a thermosuit and hot or cold food and drinks.

SETTING

Tertiary narcolepsy referral center in a university hospital

PATIENTS OR OTHER PARTICIPANTS

Eight patients (5 males) diagnosed with narcolepsy with cataplexy according to the ICSD-2 criteria (mean age +/- SD: 28.6 +/- 6.4, range 18-35 years).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

MWT sleep latency and PVT response speed.

RESULTS

Compared to core cooling, core warming attenuated the typical decline in PVT response speed with increasing time-on-task by 25% (P = 0.02). Compared to distal skin warming, distal skin cooling increased the time that the patients were able to maintain wakefulness by 24% (distal warming: 1.88 min. vs. distal warming: 2.34 min.; P < 0.01).

CONCLUSIONS

Core body and skin temperatures causally affect vigilance and sleepiness in narcolepsy. This could lead to future practical applications.

Sodium oxybate: a review of its use in the management of narcolepsy

Sodium oxybate (Xyrem) is the sodium salt of the CNS depressant gamma-hydroxybutyric acid (GHB) and is therefore subject to prescription restrictions. It is approved in the US for the treatment of cataplexy and excessive daytime sleepiness (EDS) in patients with narcolepsy, and in the EU for the treatment of narcolepsy with cataplexy. Sodium oxybate is generally well tolerated and effective in the treatment of symptoms of narcolepsy with cataplexy. While its short half-life necessitates twice-nightly administration, it is highly effective in reducing the frequency of cataplexy, improving sleep architecture and reducing EDS in patients with narcolepsy. Sodium oxybate therefore offers a valuable alternative or addition to the use of TCAs, SSRIs and stimulants in the treatment of the symptoms of narcolepsy including cataplexy and EDS.

Narcolepsy and familial advanced sleep-phase syndrome: molecular genetics of sleep disorders

Sleep disorders are very prevalent and represent an emerging worldwide epidemic. However, research into the molecular genetics of sleep disorders remains surprisingly one of the least active fields. Nevertheless, rapid progress is being made in several prototypical disorders, leading recently to the identification of the molecular pathways underlying narcolepsy and familial advanced sleep-phase syndrome. Since the first reports of spontaneous and induced loss-of-function mutations leading to hypocretin deficiency in human and animal models of narcolepsy, the role of this novel neurotransmission pathway in sleep and several other behaviors has gained extensive interest. Also, very recent studies using an animal model of familial advanced sleep-phase syndrome shed new light on the regulation of circadian rhythms.

Therapeutic advances in narcolepsy

Narcolepsy treatment has changed dramatically over the last century. For the treatment of sleepiness in narcolepsy, we have progressed from the early use of caffeine. We have available a variety of different stimulants, and a wake-promoting agent, modafinil, which is widely regarded as the first-line medication for narcolepsy. Cataplexy is managed by medications whereas behavioral treatment, such as avoidance of emotion, was the only treatment available in the past. Following the widespread use of antidepressant medications for cataplexy, we now have sodium oxybate, which works by an unknown mechanism but is the only Food and Drug Administration (FDA)-approved medication for cataplexy. We also recognize that other sleep disorders can occur in narcolepsy, such as obstructive sleep apnea syndrome or rapid eye movement sleep behavior disorder, and new treatments allow these comorbid conditions to be effectively treated. However, although we cannot cure narcolepsy, the current treatments for excessive sleepiness and cataplexy can be effective for many patients. We are improving the quality of life for our patients without producing clinically significant adverse effects. We need new therapeutic advances and several medications that work, though different mechanisms are likely to be available in the near future.

Narcolepsy with cataplexy

Narcolepsy with cataplexy is a disabling sleep disorder affecting 0.02% of adults worldwide. It is characterised by severe, irresistible daytime sleepiness and sudden loss of muscle tone (cataplexy), and can be associated with sleep-onset or sleep-offset paralysis and hallucinations, frequent movement and awakening during sleep, and weight gain. Sleep monitoring during night and day shows rapid sleep onset and abnormal, shortened rapid-eye-movement sleep latencies. The onset of narcolepsy with cataplexy is usually during teenage and young adulthood and persists throughout the lifetime. Pathophysiological studies have shown that the disease is caused by the early loss of neurons in the hypothalamus that produce hypocretin, a wakefulness-associated neurotransmitter present in cerebrospinal fluid. The cause of neural loss could be autoimmune since most patients have the HLA DQB1*0602 allele that predisposes individuals to the disorder. Treatment is with stimulant drugs to suppress daytime sleepiness, antidepressants for cataplexy, and gamma hydroxybutyrate for both symptoms. Because narcolepsy is an under-recognised disease, it is important that general practitioners and other primary health-care workers identify abnormal daytime sleepiness early.

Analysis of extended HLA haplotypes in multiple sclerosis and narcolepsy families confirms a predisposing effect for the class I region in Tasmanian MS patients

Human leucocyte antigen (HLA)-DRB1*15 is associated with predisposition to multiple sclerosis (MS), although conjecture surrounds the possible involvement of an alternate risk locus in the class I region of the HLA complex. We have shown previously that an alternate MS risk allele(s) may be encompassed by the telomerically extended DRB1*15 haplotype, and here, we have attempted to map the putative variant. Thirteen microsatellite markers encompassing a 6.79-megabase (D6S2236-G51152) region, and the DRB1 and DQB1 genes, were genotyped in 166 MS simplex families and 104 control families from the Australian State of Tasmania and 153 narcolepsy simplex families (trios) from the USA. Complementary approaches were used to investigate residual predisposing effects of microsatellite alleles comprising the extended DRB1*15 haplotype taking into account the strong predisposing effect of DRB1*15: (1) Disease association of the extended DRB1*15 haplotype was compared for MS and narcolepsy families--predisposing effects were observed for extended class I microsatellite marker alleles in MS families, but not narcolepsy families; (2) disease association of the extended DRB1*15 haplotype was investigated after conditioning MS and control haplotypes on the absence of DRB1*15--a significant predisposing effect was observed for a 627-kb haplotype (D6S258 allele 8-MOGCA allele 4; MOG, myelin oligodendrocyte glycoprotein) spanning the extended class I region. MOGCA allele 4 displayed the strongest predisposing effect in DRB1*15-conditioned haplotypes (p = 0.0006; OR 2.83 [1.54-5.19]). Together, these data confirm that an alternate MS risk locus exists in the extended class I region in Tasmanian MS patients independent of DRB1*15.

Low-resolution brain electromagnetic tomography (LORETA) identifies brain regions linked to psychometric performance under modafinil in narcolepsy

Low-resolution brain electromagnetic tomography (LORETA) showed a functional deterioration of the fronto-temporo-parietal network of the right hemispheric vigilance system in narcolepsy and a therapeutic effect of modafinil. The aim of this study was to determine the effects of modafinil on cognitive and thymopsychic variables in patients with narcolepsy and investigate whether neurophysiological vigilance changes correlate with cognitive and subjective vigilance alterations at the behavioral level. In a double-blind, placebo-controlled crossover design, EEG-LORETA and psychometric data were obtained during midmorning hours in 15 narcoleptics before and after 3 weeks of placebo or 400 mg modafinil. Cognitive investigations included the Pauli Test and complex reaction time. Thymopsychic/psychophysiological evaluation comprised drive, mood, affectivity, wakefulness, depression, anxiety, the Symptom Checklist 90 and critical flicker frequency. The Multiple Sleep Latency Test (MSLT) and the Epworth Sleepiness Scale (ESS) were performed too. Cognitive performance (Pauli Test) was significantly better after modafinil than after placebo. Concerning reaction time and thymopsychic variables, no significant differences were observed. Correlation analyses revealed that a decrease in prefrontal delta, theta and alpha-1 power correlated with an improvement in cognitive performance. Moreover, drowsiness was positively correlated with theta power in parietal and medial prefrontal regions and beta-1 and beta-2 power in occipital regions. A less significant correlation was observed between midmorning EEG LORETA and the MSLT; between EEG LORETA and the ESS, the correlation was even weaker. In conclusion, modafinil did not influence thymopsychic variables in narcolepsy, but it significantly improved cognitive performance, which may be related to medial prefrontal activity processes identified by LORETA.

DQB1*0301 and DQB1*0601 Modulate Narcolepsy Susceptibility in Koreans

The association of narcolepsy with HLA-DQB1*0602 is established in Japanese, African-Americans, European, and North American Caucasians. We examined DRB1, DRB3, DRB4, DRB5, DQA1, and DQB1 in 163 patients with centrally mediated daytime sleepiness (100 with narcolepsy) and 211 Korean controls. In this population, the DQB1*0602 association was always evident in the context of the DRB1*1501-DQA1*0102-DQB1*0602 haplotype. The DQB1*0602 association was highest in cases with hypocretin deficiency (100% vs 13% in controls), most of which had narcolepsy-cataplexy (81%). A weaker DQB1*0602 (45%) association was present in cases without cataplexy. No human leukocyte antigen (HLA) association was present in idiopathic hypersomnia or in cases with normal cerebrospinal fluid (CSF) hypocretin-1. As in other populations, DQB1*0602 homozygosity increased risk in cases with cataplexy and/or hypocretin deficiency (odds ratio = 2.0 vs heterozygotes). Non-DQB1*0602 allelic effects were also observed but could not be interpreted in the context of DQB1*0602 overabundance and linkage disequilibrium. We therefore next analyzed compound heterozygote effects in 77 subjects with either hypocretin deficiency or cataplexy and one copy of DRB1*1501-DQA1*0102-DQB1*0602, a sample constructed to maximize etiologic homogeneity. In this analysis, we found additional predisposing effects of DQB1*0301 and protective effects for DQA1*0103-DQB1*0601. Unexpectedly, the predisposing effects of DQB1*0301 were present in the context of various DQA1-bearing haplotypes. A predisposing effect of DQA1*0303 was also suggested. These results indicate a remarkable consistency in the complex HLA association present in narcolepsy across multiple ethnic groups.

Excessive daytime sleepiness: considerations for the psychiatrist

Excessive daytime sleepiness or pathologic sleepiness is a complaint found in patients who experience somnolence at unwanted times and adversely affects their daytime function. Although psychiatric illness, chronic medical illness, or medication side effects may be causes for fatigue, insufficient sleep is the most common cause of excessive daytime sleepiness in the general population. When an individual complains of frank sleepiness, in addition to insufficient sleep, important considerations in these patients are disturbances in the normal homeostatic mechanisms that govern sleep and wakefulness. This article summarizes the clinical presentation, the differential diagnosis, commonly used diagnostic tools, and treatment options for patients complaining of excessive daytime sleepiness.

Sodium oxybate: neurobiology and clinical efficacy

Sodium oxybate is the sodium salt of γ-hydroxybutyrate (GHB), an endogenous short-chain fatty acid that is speculated to function as a neurotransmitter in the mammalian CNS. Pharmacodynamic effects of exogenously-administered sodium oxybate may include modulating the release of neurotransmitters, including γ-aminobutyric acid, dopamine, endogenous opioids and serotonin, and stimulating release of growth hormone. It is rapidly absorbed, with approximately 25% bioavailability and a plasma half-life of 40–60 min, necessitating twice-nightly dosing. Sodium oxybate is indicated for the treatment of cataplexy and excessive daytime sleepiness in patients with narcolepsy, and has been shown to improve disrupted night-time sleep and increase Stage 3 and 4 (slow-wave restorative) sleep in this patient population. The most common adverse events reported in clinical trials in patients with narcolepsy include headache, nausea, dizziness, nasopharyngitis, somnolence, vomiting and urinary incontinence.

Paroxysmal Motor Disorders of Sleep: The Clinical Spectrum and Differentiation from Epilepsy

The diagnosis of paroxysmal events in sleep represents a significant challenge for the clinician, with the distinction of nocturnal epilepsy from nonepileptic sleep disorders often the primary concern. Diagnostic error or uncertainty is not uncommon in this situation, particularly with respect to nocturnal frontal lobe epilepsy (NFLE), which has a variable and often unusual presentation. Such errors can be minimized if the range of nonepileptic disorders with motor activity in sleep is fully appreciated. Here we review these disorders, before discussing the important clinical and electrographic features that allow their accurate differentiation from seizures. Particular emphasis is placed on the differentiation of nocturnal frontal lobe epilepsy from non-rapid eye movement (NREM) arousal disorders and other parasomnias. The value of recording episodes with video EEG polysomnography is discussed.

Possible confusion between primary hypersomnia and adult attention-deficit/hyperactivity disorder

We explored the possibility of diagnostic confusion between hypersomnias of central origin (narcolepsy and idiopathic hypersomnia, IH) and the adult form of attention-deficit/hyperactivity disorder (ADHD). We included 67 patients with narcolepsy, 7 with IH and 61 with ADHD. All patients completed the Epworth Sleepiness Scale and the ADHD Rating Scale. We found that 18.9% of the hypersomnia patients fulfilled the self-reported criteria for ADHD in adulthood, compared with 77% of the ADHD patients. A score > or =12 on the Epworth Sleepiness Scale (usually regarded to indicate excessive daytime sleepiness) was found in 37.7% of the ADHD patients compared 95.9% of the hypersomnia patients. In ADHD patients, inattention scores correlated with the excessive daytime sleepiness score. We conclude that one should be aware of possible diagnostic confusion between narcolepsy or IH and adult ADHD when using self-report questionnaires. The high percentage of symptom overlap found in our study raises questions about possible misdiagnosing of both conditions, comorbidity with sleep problems in adult ADHD, and the validation of the used scales. It remains unclear whether our findings indicate pathophysiological overlap.

Startle syndromes

Startle syndromes consist of three heterogeneous groups of disorders with abnormal responses to startling events. The first is hyperekplexia, which can be split up into the "major" or "minor" form. The major form of hyperekplexia is characterised by excessive startle reflexes, startle-induced falls, and continuous stiffness in the neonatal period. This form has a genetic basis: mutations in the alpha1 subunit of the glycine receptor gene, GLRA1, or related genes. The minor form, which is restricted to excessive startle reflexes with no stiffness, has no known genetic cause or underlying pathophysiological substrate. The second group of startle syndromes are neuropsychiatric, in which excessive startling and various additional behavioural features occur. The third group are disorders in which startling stimuli can induce responses other than startle reflexes, such as startle-induced epilepsy. Diagnosis of startle syndromes depends on clinical history, electromyographic studies, and genetic screening. Further study of these disorders may enable improved discrimination between the different groups.

Cataplexy leading to the diagnosis of Niemann-Pick disease type C

Cataplexy in childhood is a rare and often misdiagnosed symptom. It is described as a brief episode of bilateral loss of muscle tone with intact consciousness, triggered by a variety of strong emotions and in particular with unexpected laughter. This report presents a 9-year old male with progressive cerebellar and pyramidal symptoms and a cognitive decline since the age of 4. His recently developed "drop attacks" on laughter were recognized as cataplexy and led to the diagnosis of Niemann-Pick type C disease. With biochemical studies this diagnosis, a lysosomal storage disease, was confirmed. With cataplexy narcolepsy, Niemann-Pick type C disease, Norrie disease, Prader-Willi syndrome, and Coffin-Lowry syndrome are associated disorders. Recognition of cataplexy in children with concomitant neurologic symptoms may lead to an early and straight diagnosis of one of these disorders.

Integration of feeding and spontaneous physical activity: role for orexin

Spontaneous physical activity is activity that is non-volitional, or subconscious, such as fidgeting and shifting in one's seat, and time spent moving (standing and ambulating). Recent evidence indicates that spontaneous physical activity, and the resulting thermogenesis (non-exercise activity thermogenesis) may be regulated by brain systems. A large number of brain areas, with their associated neurotransmitter populations and connectivity, participate in the regulation of feeding behavior by acting as energy sensing and modulating centers. Although less well characterized, it is likely that a multitude of neurotransmitters and brain areas act to mediate spontaneous physical activity. These two behaviors, feeding and spontaneous physical activity, affect energy intake and expenditure and thus are important to body weight. Interestingly, often the two behaviors are affected simultaneously; when feeding is affected, so too is spontaneous physical activity, and both food intake and physical activity (whether spontaneous or volitional) influence activity of brain areas important to both. Several brain areas and neuropeptides are important to feeding and spontaneous physical activity. The lateral hypothalamus is one area that appears important to both behaviors, as stimulation or lesion of this region produces alterations in feeding behavior and spontaneous physical activity. Orexin neurons, with their central location in the lateral hypothalamus, widespread projections and connectivity to other brain areas important to energy homeostasis, are well situated to perform an integrative function. This review focuses on how hypothalamic orexins participate in both feeding and spontaneous physical activity, and provides potential models for the integration of signals important to both.

Does the arousal system contribute to near death experience?

The neurophysiologic basis of near death experience (NDE) is unknown. Clinical observations suggest that REM state intrusion contributes to NDE. Support for the hypothesis follows five lines of evidence: REM intrusion during wakefulness is a frequent normal occurrence, REM intrusion underlies other clinical conditions, NDE elements can be explained by REM intrusion, cardiorespiratory afferents evoke REM intrusion, and persons with an NDE may have an arousal system predisposing to REM intrusion. To investigate a predisposition to REM intrusion, the life-time prevalence of REM intrusion was studied in 55 NDE subjects and compared with that in age/gender-matched control subjects. Sleep paralysis as well as sleep-related visual and auditory hallucinations were substantially more common in subjects with an NDE. These findings anticipate that under circumstances of peril, an NDE is more likely in those with previous REM intrusion. REM intrusion could promote subjective aspects of NDE and often associated syncope. Suppression of an activated locus ceruleus could be central to an arousal system predisposed to REM intrusion and NDE.

Immunohistochemical screening for autoantibodies against lateral hypothalamic neurons in human narcolepsy

Most human patients with narcolepsy have no detectable hypocretin-1 in their cerebrospinal fluid. The cause of this hypocretin deficiency is unknown, but the prevailing hypothesis states that an autoimmune-mediated mechanism is responsible. We screened for the presence of autoantibodies against neurons in the lateral hypothalamus in 76 patients and 63 controls, using immunohistochemistry. Autoantibodies were present in two patients, but also in two controls. However, one of the patients had a clearly different staining pattern and nerve endings of immunolabeled cells were found to project onto hypocretin-producing neurons, suggesting a possible pathophysiological role. Humoral immune mechanisms appear not to play a role in the pathogenesis of narcolepsy, at least not in the clinically overt stage of the disease.

Narcolepsy with cataplexy in early childhood

Narcolepsy is a rare neurologic sleep disorder with morbidity associated with functional impairment and frequent delay in diagnosis. Symptoms typically manifest in adolescence or early adulthood, but diagnosis of narcolepsy has been reported in early childhood. Diagnosis rates are as low as 50% of the total population of patients with narcolepsy and are delayed as much as 10 years after disease onset due to inadequate patient-physician communication and/or misdiagnosis. I present the complexity of diagnosing narcolepsy in early childhood in a patient with cataplexy that started soon after independent ambulation at age 10 months.

Cataplexy associated with narcolepsy: epidemiology, pathophysiology and management

Although narcolepsy was first described over 100 years ago, most of what is known about the pathological changes in the CNS that are responsible for this unusual disease has been learned during the past few years. It is now known that narcolepsy is caused by the loss of a relatively few neurons that are responsible for producing the neuropeptide hypocretin in the CNS. The onset of narcolepsy typically occurs in early adulthood and may consist of a variety of symptoms; however, cataplexy (an abrupt, bilateral loss of skeletal muscle tone) is most specific to narcolepsy. TCAs were found to be beneficial for the treatment of cataplexy over 40 years ago and, more recently, the SSRIs have been used to treat the condition. The recent availability of sodium oxybate (the first drug to receive regulatory approval for the treatment of cataplexy) represents a significant advance in the treatment of narcolepsy, as it is highly efficacious for the treatment of cataplexy and shows promise for the treatment of excessive sleepiness and for improving sleep quality in patients with narcolepsy.

The relationship between sleep disturbance and depression

This paper focuses on several aspects of the relationship between sleep and depression, with particular attention to objective factors and subjective perceptions. It does not address the effect that antidepressants have on sleep, nor does it explore the wider implications of the types and course of depression, age, or other psychiatric conditions. "Normal sleep" is explored, examining typical sleep architecture in individuals without sleep disorders, psychiatric conditions or physical illness. Sleep disorders are reviewed and examined to present the nature of the disturbance and the role that they may play in depression, with particular attention paid to insomnia. Studies have identified a sub-group of insomnia patients (highly distressed poor sleepers), who appear to be less satisfied with their sleep quality than "low distressed poor sleepers", even though they did not differ on sleep timing perceptions. Recent work has shown that depressed individuals to be less satisfied with sleep quality than healthy controls, even though they did not differ on sleep timing perceptions. The evidence presented here supports the view that subjective sleep perceptions play an important role in depression. Poor subjective perceptions of sleep in depression may be associated with faulty cognitions. This has been found extensively in insomnia, but is under-researched in depression.

The hypocretins and sleep

The hypocretins (also called the orexins) are two neuropeptides derived from the same precursor whose expression is restricted to a few thousand neurons of the lateral hypothalamus. Two G-protein coupled receptors for the hypocretins have been identified, and these show different distributions within the central nervous system and differential affinities for the two hypocretins. Hypocretin fibers project throughout the brain, including several areas implicated in regulation of the sleep/wakefulness cycle. Central administration of synthetic hypocretin-1 affects blood pressure, hormone secretion and locomotor activity, and increases wakefulness while suppressing rapid eye movement sleep. Most human patients with narcolepsy have greatly reduced levels of hypocretin peptides in their cerebral spinal fluid and no or barely detectable hypocretin-containing neurons in their hypothalamus. Multiple lines of evidence suggest that the hypocretinergic system integrates homeostatic, metabolic and limbic information and provides a coherent output that results in stability of the states of vigilance.

Conditions of Primary Excessive Daytime Sleepiness

Excessive daytime somnolence is a prevalent problem in medical practice and in society. It exacts a great toll in quality of life, personal and public safety, and productivity. The causes of EDS are myriad, and careful evaluation is needed to determine the cause in each case. Although much progress has been made in discovering the pathophysiology of narcolepsy, much more remains to be understood, and far less is known about other primary conditions of EDS. Several methods have been developed to assess EDS, although each of them has limitations. Treatment is available for the great majority of cases.

Periodic limb movements and other movement disorders in sleep: neuropsychiatric dimensions

Movement disorders such as Parkinson's disease and Tourette's syndrome, primarily manifest during wakefulness, intrude into sleep. There are some disorders, however, such as periodic limb movements in sleep, restless legs syndrome, paroxysmal nocturnal dystonia, bruxism, and somnambulism, which occur primarily during sleep. The diagnosis and management of these disorders pose a challenge to neuropsychiatric practice, not only because they may be difficult to distinguish from other neuropsychiatric disorders, but also because psychiatric disorders are often co-morbid with them. Study of these disorders is necessary for an understanding of the interaction of sleep and movement, and how disturbance in one may affect the other.

[Sleep-wake cycle mechanisms]

Neurochemically distinct systems interact regulating sleep and wakefulness. Wakefulness is promoted by aminergic, acetylcholinergic brainstem and hypothalamic systems. Each of these arousal systems supports wakefulness and coordinated activity is required for alertness and EEG activation. Neurons in the pons and preoptic area control rapid eye movement and non-rapid eye movement sleep. Mutual inhibition between these wake- and sleep-regulating systems generate behavioral states. An up-to-date understanding of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.

The association between narcolepsy and REM behavior disorder (RBD)

BACKGROUND AND PURPOSE

Rapid eye movement (REM) sleep Behavior Disorder (RBD) is a movement disorder associated with loss of REM-related muscle atonia and is characterized by complex, vigorous and frequently violent dream-enacting behavior during REM sleep. RBD is usually idiopathic or secondary to neurological problems such as Parkinson's disease. This study looked at the association of RBD with another sleep disorder, narcolepsy.

PATIENTS AND METHODS

Seventy-eight questionnaires were sent to known narcoleptics chosen at random from those with contact details available at the center. The questionnaire addressed current narcolepsy symptoms, medication use and symptoms of RBD. Positive questionnaire results were followed up with a telephone interview. Limited polysomnography (PSG) data was also analyzed.

RESULTS

Fifty-five patients responded (response rate 71%). Of these, 20 (36%) had symptoms suggestive of RBD. The typical RBD patient is an older male (mean age of onset 60.9 years, 87% male); however, in this study, females were as likely to have RBD as males, and the mean age was 41 years. Sixty-eight percent of patients who regularly experienced cataplexy and the associated symptoms of narcolepsy (sleep paralysis, hypnogogic hallucinations and automatic behavior) had RBD, compared to 14% of those who never or rarely experienced these symptoms.

CONCLUSION

This study implies a stronger relationship between these disorders than a previously published figure of 7-12% This is clinically significant as RBD is a potentially distressing but readily treatable disorder. It follows that narcoleptics, especially those with cataplexy and other associated symptoms, should be questioned about symptoms of RBD and treated accordingly. Similarly, anyone presenting with RBD should be assessed for symptoms of narcolepsy, particularly if female or of a younger age group than would otherwise be expected.

Altered setting of the pituitary-thyroid ensemble in hypocretin-deficient narcoleptic men

Narcolepsy is a sleep disorder caused by disruption of hypocretin (orexin) neurotransmission. Injection of hypocretin-1 acutely suppresses TRH and TSH release in rats. In contrast, subchronic administration does not appear to affect the hypothalamo-pituitary-thyroid ensemble in animals. We explored (in 7 patients and 7 controls) whether hypocretin deficiency impacts circulating TSH levels and circadian timing of TSH release in narcoleptic humans. Plasma TSH concentration profiles (blood samples taken at 10-min intervals during 24 h) and TSH levels in response to TRH injection were analyzed by Cluster, robust regression, approximate entropy (ApEn), and deconvolution. Circulating TSH levels were lower in patients, which was primarily attributable to lower pulse amplitude and nadir concentrations. TSH secretion correlated positively with mean 24-h leptin levels (R2 = 0.46, P = 0.02) and negatively with amount of sleep (R2 = 0.29, P = 0.048). Pattern-synchrony between 24-h leptin and TSH concentrations was demonstrated by significant cross-correlation and cross-ApEn analyses with no differences between controls and patients. Sleep onset was closely associated with a fall in circulating TSH. Features of diurnal rhythmicity of circulating TSH fluctuations were similar in patients and controls, with the acrophase occurring shortly after midnight. Thyroxine and triiodothyronine concentrations were similar in patients and controls and did not display a diurnal rhythm. The response of plasma TSH levels to TRH was also similar in both groups. Sleep patterns in narcoleptics were significantly disorderly compared with controls, as measured by ApEn (P = 0.006). In summary, circulating TSH concentrations are low in hypocretin-deficient narcoleptic men, which could be attributable to their low plasma leptin levels and/or their abnormal sleep-wake cycle.

Trend and area variation in amphetamine prescription usage among children and adolescents in Michigan

The increased use of stimulant medications for children and teenagers is an ongoing issue of professional and public concern. Unlike methylphenidate, the growth of prescriptions and patterns of utilization of amphetamines for pediatric populations have not been well documented. The study objectives were to describe the trends of amphetamine prescription utilization among pediatric age groups in Michigan and to compare area variations. A population-based computerized data set from the state of Michigan was used to extract all outpatient prescriptions for Schedule II amphetamines dispensed from 1990 to 1997. The prescribing rates by age groups and by counties were computed with the projected population size of corresponding years, and mapped and analyzed with spatial statistical methods. Counties that did not conform to the global spatial dependence pattern in the prescription rate were identified using Moran scatter plot. A total of 236,661 outpatient prescriptions for amphetamines were dispensed in Michigan during the time frame, including less than 1% for methamphetamine, 24.5% for amphetamine, and 74.8% for dextroamphetamine. The prescribing rate was highest among children 10-14 years old (380 prescriptions per 10,000 people) in 1997, followed by children 5-9 years old (253 prescriptions per 10,000). Over the 8-year period, the prescribing rates of amphetamines increased significantly, ranging from 380% for children 2-4 years to 817% for teenagers older than 14 years. The rates among counties ranged from 60 to 1648 per 10,000 children 5-14 years old, with the highest prescribing rates in the northwestern regions of Michigan. Although spatial dependence explained 36% of the variance, the area variations that are unaccounted for are still considerable. In conclusion, there were substantial increases and unexplained area variations in amphetamine usage in Michigan during the study period. Both phenomena require awareness and evaluation from researchers, policy makers, clinicians, and the public.

Sodium oxybate for the treatment of narcolepsy

Narcolepsy, a lifelong disease with diverse symptoms, poses a therapeutic challenge to physicians. Psychomotor stimulants are used to provide some relief from excessive sleepiness, whereas a variety of other medications have traditionally been used to treat the other symptoms of this disorder. Cataplexy, consisting of sudden episodes of bilateral skeletal muscle weakness, has long been treated with tricyclic antidepressants or selective serotonin re-uptake inhibitors. Although these drugs have brought relief to some patients, they cause intolerable adverse effects in others, whereas still others become tolerant to their beneficial effects. In July of 2002, sodium oxybate was approved by the US FDA for the treatment of cataplexy, representing a significant advance in the treatment of this unusual disease. The following drug evaluation summarises the role of this novel medication in the practice of sleep medicine.

Convergence of circadian and sleep regulatory mechanisms on hypocretin-1

Hypocretin is a potential regulator of sleep and wakefulness and its levels fluctuate with the day-night cycle with high levels during the animal's activity period. Whether the daily fluctuations are driven endogenously or by external light cycles is unknown. We investigated the circadian and homeostatic regulation of hypocretin in the absence of environmental light cycles. To this purpose we performed repetitive samplings of cerebrospinal fluid in rats through implanted microcannulas in the cisterna magna and determined hypocretin-1 levels by radioimmunoassay. These experiments were also performed in rats that received a lesion of the suprachiasmatic nucleus (SCN), a major pacemaker for circadian rhythms in mammals. The results showed sustained rhythmicity of hypocretin in constant dim red light in control animals. SCN-lesioned animals showed no circadian rhythms in hypocretin and mean hypocretin levels were remarkably low. The results indicate that the SCN is indispensable for rhythmicity in hypocretin and induces a daily increase in hypocretin levels during the animal's active phase. Additional sleep deprivation experiments were carried out to investigate homeostatic regulation of hypocretin. Hypocretin levels increased in response to sleep deprivation in both control and SCN-lesioned animals, demonstrating that sleep homeostatic control of hypocretin occurs independently from the SCN. Our data indicate that the circadian pacemaker of the SCN and sleep homeostatic mechanisms converge on one single sleep regulatory substance.

Emerging drugs for narcolepsy

Narcolepsy is characterised by excessive daytime sleepiness, usually associated with cataplexy, hypnagogic hallucinations, sleep paralysis and fragmented nocturnal sleep. Although uncommon, it results in significant disability. Most cases occur sporadically, but genetic factors probably form a susceptibility background on which unknown environmental triggers act. The hypocretin system is strongly implicated in the development of narcolepsy. Cerebrospinal fluid levels of hypocretin-1 are significantly reduced in narcoleptic subjects with cataplexy. Despite the advances in our understanding of narcolepsy, current therapy is primarily symptomatic. Stimulants (standard and novel) combat excessive daytime sleepiness. Antidepressants (tricyclics, dual-action or selective serotonin re-uptake inhibitors) and sodium oxybate are anticataplexy agents. Hypnagogic hallucinations and sleep paralysis respond to antidepressants. Sodium oxybate consolidates sleep. Novel and experimental treatments include histamine antagonists, hypocretin agonists, slow-wave sleep enhancers, intravenous gamma-globulin, tramadol and corticosteroids.

EEG-mapping differences between narcolepsy patients and controls and subsequent double-blind, placebo-controlled studies with modafinil

The aim of the present study was to investigate the role of EEG mapping as an objective and quantitative measure of vigilance in untreated and modafinil-treated narcoleptics, and compare it with the conventional neurophysiological method of the Multiple Sleep Latency Test (MSLT) and the subjective Epworth Sleepiness Scale (ESS). In 16 drug-free narcoleptics and 16 normal controls a baseline 3-min vigilance-controlled EEG (V-EEG) and a 4-min resting EEG (R-EEG) were recorded during midmorning hours. Thereafter, in a double-blind, placebo-controlled crossover design, patients were treated with a 3-week fixed titration of modafinil (200, 300, 400 mg) and placebo. EEG-mapping, MSLT and ESS measures were obtained before and at the end of the third week of therapy. Statistical overall analysis by means of the omnibus significance test demonstrated significant EEG differences between untreated patients and controls in the resting condition only (R-EEG). Subsequent univariate analysis revealed an increase in absolute and relative theta power, a decrease in alpha-2 and beta power as well as a slowing of the dominant frequency and the centroids of the alpha, beta and total power spectrum and thus objectified a vigilance decrement in narcolepsy. Modafinil 400 mg/d significantly improved vigilance as compared with placebo (p < or = 0.01), inducing changes opposite to the aforementioned baseline differences (key-lock principle). The MSLT and the ESS also improved under modafinil as compared with placebo, but changes were less consistent. Spearman rank correlations revealed the highest correlations between EEG mapping and the ESS, followed by those between EEG mapping and the MSLT, while the lowest correlation was found between the MSLT and the ESS. In conclusion, EEG mapping is a valuable instrument for measuring vigilance decrements in narcolepsy and their improvement under psychostimulant treatment.

Investigation of sleep disorders

Polysomnography or sleep study is the main investigation for paediatric sleep disorders. It involves the continuous and simultaneous recording of multiple physiological parameters evaluating sleep and respiration. It is most commonly used to diagnose obstructive sleep apnoea and to monitor nocturnal non-invasive ventilation requirements of children. Its role in other sleep related breathing disorders, narcolepsy and parasomnias is discussed.

Functional involvement of cerebral cortex in human narcolepsy

The pathophysiology of human narcolepsy is still poorly understood. The hypoactivity of some neurotransmitter systems has been hypothesised on the basis of the canine model. To determine whether narcolepsy is associated with changes in excitability of the cerebral cortex, we assessed the excitability of the motor cortex with transcranial magnetic stimulation (TMS) in 13 patients with narcolepsy and in 12 control subjects. We used several TMS paradigms that can provide information on the excitability of the motor cortex. Resting and active motor thresholds were higher in narcoleptic patients than in controls and intracortical inhibition was more pronounced in narcoleptic patients. No changes in the other evaluated measures were detected. These results are consistent with an impaired balance between excitatory and inhibitory intracortical circuits in narcolepsy that leads to cortical hypoexcitability. We hypothesise that the deficiency of the excitatory hypocretin/orexin-neurotransmitter-system in narcolepsy is reflected in changes of cortical excitability since circuits originating in the lateral hypothalamus and in the basal forebrain project widely to the neocortex, including motor cortex. This abnormal excitability of cortical networks could be the physiological correlate of excessive daytime sleepiness and it could be the substrate for allowing dissociated states of wakefulness and sleep to emerge suddenly while patients are awake, which constitute the symptoms of narcolepsy.

Women's sleep in health and disease

A huge amount of knowledge about sleep has accumulated during the last 5 decades following the discovery of rapid eye movement (REM) sleep. Nevertheless, there are numerous areas of considerable ignorance. One of these concerns the particularities of sleep in women. Most basic and clinical studies have been performed in male subjects, and only very recently research groups around the world have addressed women's sleep in health and disease. In this review, we summarize the present knowledge on the influence of oestrogens on the brain and on the distinctive changes of sleep across the menstrual cycle, during pregnancy and menopause. In addition, studies in female rodents are reviewed as well as the knowledge on female peculiarities regarding the interactions between sleep regulation and age-related changes in circadian rhythms. We also address specific aspects of sleep loss and sleep disorders in women. Finally, very recent studies on the sociology of sleep are summarized and future directions in the field are discussed.

EEG-tomographic studies with LORETA on vigilance differences between narcolepsy patients and controls and subsequent double-blind, placebo-controlled studies with modafinil

The aim of the present study was to identify brain regions associated with vigilance in untreated and modafinil-treated narcoleptic patients by means of low-resolution brain electromagnetic tomography (LORETA). 16 drug-free narcoleptics and 16 normal controls were included in the baseline investigation. Subsequently patients participated in a double-blind, placebo-controlled crossover study receiving a three-week fixed titration of modafinil (200, 300, 400 mg) and placebo. Measurements comprised LORETA, the Multiple Sleep Latency Test (MSLT) and the Epworth Sleepiness Scale (ESS) obtained before and after three weeks' therapy. Statistical overall analysis by means of the omnibus significance test demonstrated significant inter-group differences in the resting (R-EEG), but not in the vigilance-controlled recordings (V-EEG). Subsequent univariate analysis revealed a decrease in alpha-2 and beta 1-3 power in prefrontal, temporal and parietal cortices, with the right hemisphere slightly more involved in this vigilance decrement. Modafinil 400 mg/d as compared with placebo induced changes opposite to the aforementioned baseline differences (key-lock principle) with a preponderance in the left hemisphere. This increase in vigilance resulted in an improvement in the MSLT and the ESS. LORETA provided evidence of a functional deterioration of the fronto-temporo-parietal network of the right-hemispheric vigilance system in narcolepsy and a therapeutic effect of modafinil on the left hemisphere, which is less affected by the disease.

Pulsatile LH release is diminished, whereas FSH secretion is normal, in hypocretin-deficient narcoleptic men

Hypocretin (orexin) peptides are involved in the regulation of energy balance and pituitary hormone release. Narcolepsy is a sleep disorder characterized by disruption of hypocretin neurotransmission. Pituitary LH secretion is diminished in hypocretin-deficient animal models, and intracerebroventricular administration of hypocretin-1 activates the hypothalamo-pituitary-gonadal axis in rats. We evaluated whether hypocretin deficiency affects gonadotropin release in humans. To this end, we deconvolved 24-h serum concentrations of LH and FSH in seven hypocretin-deficient narcoleptic males (N) and seven controls (C) matched for age, body mass index, and sex. Basal plasma concentrations of testosterone, estradiol, and sex hormone-binding globulin were similar in both groups. Mean 24-h LH concentration was significantly lower in narcolepsy patients [3.0 +/- 0.4 (N) vs. 4.2 +/- 0.3 (C) U/l, P = 0.01], which was primarily due to a reduction of pulsatile LH secretion [23.5 +/- 1.6 (N) vs. 34.3 +/- 4.9 (C) U.l(-1).24 h(-1), P = 0.02]. The orderliness of LH and FSH secretion, quantitated by the approximate entropy statistic, was greater in patients than in controls. In contrast, all other features of FSH release were similar in narcoleptic and control groups. Also, LH and FSH secretions in response to intravenous administration of 100 microg of GnRH were similar in patients and controls. These data indicate that endogenous hypocretins are involved in the regulation of the hypothalamo-pituitary-gonadal axis activity in humans. In particular, reduced LH release in the face of normal pituitary responsivity to GnRH stimulation in narcoleptic men suggests that hypocretins promote endogenous GnRH secretion.

Expression of a poly-glutamine-ataxin-3 transgene in orexin neurons induces narcolepsy-cataplexy in the rat

The sleep disorder narcolepsy has been linked to loss of hypothalamic neurons producing the orexin (hypocretin) neuropeptides. Here, we report the generation of transgenic rats expressing a human ataxin-3 fragment with an elongated polyglutamyl stretch under control of the human prepro-orexin promoter (orexin/ataxin-3 rats). At 17 weeks of age, the transgenic rats exhibited postnatal loss of orexin-positive neurons in the lateral hypothalamus, and orexin-containing projections were essentially undetectable. The loss of orexin production resulted in the expression of a phenotype with fragmented vigilance states, a decreased latency to rapid eye movement (REM) sleep and increased REM sleep time during the dark active phase. Wakefulness time was also reduced during the dark phase, and this effect was concentrated at the photoperiod boundaries. Direct transitions from wakefulness to REM sleep, a defining characteristic of narcolepsy, occurred frequently. Brief episodes of muscle atonia and postural collapse resembling cataplexy were also noted while rats maintained the electroencephalographic characteristics of wakefulness. These findings indicate that the orexin/ataxin-3 transgenic rat could provide a useful model of human narcolepsy.

Variants of the orexin2/hcrt2 receptor gene identified in patients with excessive daytime sleepiness and patients with Tourette's syndrome comorbidity

The orexin-2/hypocretin-2 (OX2R) receptor gene is mutated in canine narcolepsy and disruption of the prepro-orexin/hypocretin ligand gene results in both an animal model of narcolepsy and sporadic cases of the human disease. This evidence suggests that the structure of the OX2R gene, and its homologue, the OX1R gene, both members of the G protein-coupled receptor (GPCR) family, and the gene encoding the peptide ligands, the prepro-orexin/hypocretin gene, may be variables in the etiology of sleep disorders. We report a single stranded conformational polymorphism (SSCP) analysis of the coding regions of these genes in idiopathic sleep disorder patients diagnosed with excessive daytime sleepiness (EDS) (n = 28), narcolepsy (n = 28), Tourette's syndrome/chronic vocal or motor tic disorder (n = 70), and control subjects (n = 110). Two EDS patients showed a Pro11Thr change. One Tourette's syndrome patient was found to have a Pro10Ser alteration. The Pro10Ser and Pro11Thr variants were not found in non-disease populations. Analysis of the ability of the mutant receptors to mobilize calcium compared to the wild-type receptor in response to orexin agonists indicated that they resulted in decreased potency at high (etaM) concentrations of orexin ligands. Further work is warranted to study the variability of the orexin/hypocretin system in a variety of disorders characterized by EDS.

Screening for candidate gene regions in narcolepsy using a microsatellite based approach and pooled DNA

Narcolepsy is a complex sleep disorder characterized by excessive daytime sleepiness and cataplexy. Mutations in genes of the hypocretin (orexin) neurotransmitter system cause narcoleptic symptoms in animal models. The absence of hypocretin in the cerebrospinal fluid of human patients is hypothesized to originate from destruction of hypocretinergic cells in the hypothalamus, the cause of which remains unknown. Due to strong HLA association autoimmune models of narcolepsy pathogenesis are still mostly favored. Genetic predisposition factors other than HLA are likely to play a role in causing the disorder. We screened three sets of gene regions ( n=254) for association with narcolepsy using a microsatellite based approach and pooled DNA: genes related to immunity, particularly apoptosis; genes related to regulation of circadian rhythmicity; genes coding for several factors of neurotransmission. In relation to apoptosis an association was found for the BAG1 gene region. Interestingly, microsatellites representing four genomic regions related to neurotransmission revealed association with narcolepsy: COMT, DRD2, GABBR1, and HTR2A. These results, although exploratory and still to be confirmed in independent samples, support a complex pathogenetic model for narcolepsy, including disturbances of neurotransmission rather than involvement of autoimmunity.

Exploring the cytokine and endocrine involvement in narcolepsy

Narcolepsy is a disabling neurological sleep disorder characterized by excessive daytime sleepiness and abnormal REM sleep manifestations. Recently, the role of cytokines and growth hormone in the regulation of sleep and narcolepsy has been considered, and data suggest that proinflammatory cytokines may be involved in sleep and narcoleptic symptoms. Serum and clinical data were obtained from the Stanford Center for Narcolepsy Research for 39 Narcoleptics (22 Females, 17 Males, age 39+/-14.9) and 40 controls (13 Females, 27 Males, age 46+/-17.9). Plasma levels of TNF-alpha, IL-6, and human growth hormone (hGH) were measured by ELISA. TNF-alpha and IL-6 were significantly increased in narcoleptic subjects compared to controls (p=.001). Interestingly, hGH was significantly increased in narcoleptic subjects (p <.0001). There was also a significant difference in the epworth sleepiness scale (ESS) (17.7+/-4.6 vs. 5.5+/-3.2, p <.0001). These data indicate that narcoleptics, relative to controls, had higher serum levels of TNF-alpha, IL-6, and hGH. These data suggest that the dysregulation of sleep observed in narcoleptics correlates with the immune and endocrine dysregulation seen in these subjects, and the observed changes may in fact contribute to the higher likelihood of disturbed sleep and/or increased incidence of infection. Additional work is required to fully characterize connections between cytokines and narcoleptic symptomatology.

Pupil staging and EEG measurement of sleepiness

The goal of this multi-method study was to examine the validity (accuracy) of the pupillometric Alertness Level Test (ALT) as a physiologic measure of sleepiness. The study used a pooled-time series-correlation design with 16 untreated narcolepsy (8 F, 8 M), 16 untreated obstructive sleep apnea (OSA) (7 F, 9 M) and 16 healthy control (8 F, 8 M) subjects. Participants underwent EEG/polysomnography testing using standard Multiple Sleep Latency Test electrode placement concurrent with the 15 min pupillometric ALT. EEG data were examined to determine if theta power (4-7 Hz) increased during 2-s periods of proportional pupil size decreases (pupil Stage 1, 95% or more of maximal pupil size to Stage 4, 65-74% of maximal size). Printed EEG records also were visually scored. Self-report sleepiness measures included the Pittsburgh Sleep Quality Index, the Profile of Mood States and the Epworth Sleepiness Scale. Within subject groups, theta power ratios significantly increased across pupil stages for the sleep disorder groups but not for controls (theta activity increased 42% for narcoleptic and 36% for OSA subjects). Between subject groups, the amount of theta activity was significantly greater for narcoleptic and OSA subjects than that for controls. Visual EEG scoring and self-report measures were usually consistent with objective findings. The ALT is convenient, easily repeatable and less technically demanding than EEG sleepiness measures, and it deserves more comprehensive testing as a valid measure of sleepiness.