Narcolepsy

The month of birth has a seasonal effect in Chinese patients with narcolepsy and cataplexy

STUDY OBJECTIVES

We assessed the yearly seasonal, environmental effects on birth pattern in Chinese patients later diagnosed with narcolepsy and cataplexy and explored if this effect persisted in patients with symptoms onset date before, following, and after the 2009 H1N1 pandemic.

METHODS

A total of 1,942 patients with birth data information and diagnosed narcolepsy with cataplexy were included in this study. The birth month and seasonal effect of 1,064 patients born from 1970 to 2000 were compared to controls (n = 2,028,714) from the general population. Furthermore, birth season effect in 1,373 patients with definite disease onset month were compared among patients with onset date before (n = 595), following (from January 2010 to December 2010) (n = 325), and after (n = 453) the H1N1 pandemic.

RESULTS

Patients with narcolepsy and cataplexy had a significantly different seasonality from the general population (P = .027). The monthly distribution of birth month yielded a peak in November (odds ratio = 1.23 [95% confidence interval, 1.01-1.49], P = .042) and a trough in April (odds ratio = 0.68 [95% confidence interval, 0.52-0.88], P = .004). No significant difference was observed in the birth month across patients with symptom onset dates before, following, and after the 2009 H1N1 pandemic (P = .603).

CONCLUSIONS

This finding across many years of seasonal effect in Chinese narcolepsy cataplexy supports a role for early-life environmental influences on disease development.

CITATION

Guo J, Xu L, Wang J, et al. The month of birth has a seasonal effect in Chinese patients with narcolepsy and cataplexy. J Clin Sleep Med. 2022;18(2):461-467.

An Examination of History for Promoting Diversity in Neuroscience

Purpose of Review

A review of American history is presented to understand how public policy has contributed to a disproportionate burden of disease in members of underrepresented groups. A review of research conducted in the Stroke Belt provides an opportunity to examine more closely traditional and non-traditional risk factors in an effort to consider strategies for change.

Recent Findings

A diverse physician workforce has been offered as a way of improving care for our increasingly diverse populace. Given the expected increased prevalence of stroke in communities of color and the impact of stress from discrimination on health, proactive strategies to promote inclusion and equity to support diversity in perioperative neuroscience is warranted.

Summary

Public policy rooted in structural racism has left marginalized groups economically and educationally disadvantaged with less access to health care. Mistrust and fear from ongoing discrimination compels the neuroscience community to broaden their approach for developing a more reassuring and supportive educational environment for patients and trainees.

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

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

Clinical Characteristics of Cataplectic Attacks in Type 1 Narcolepsy

PURPOSE OF REVIEW

Narcolepsy is a central disorder of hypersomnolence with symptoms of excessive daytime sleepiness, sleep paralysis, and cataplexy. Cataplexy is the sudden loss of muscle tone in either the face, neck, trunk, and/or limbs, leading to a loss of voluntary muscle control. This article reviews recent research on the clinical characteristics of cataplexy.

RECENT FINDINGS

Longitudinal research in adults suggests that there may be a remission of cataplectic severity after symptom stabilization. First-line treatment options for cataplexy include sodium oxybate and pitolisant, with many drugs such as AXS-12, FT218, and JZP258 under investigation. Patients with cataplexy reported greater limitations of daily activities such as driving and exercise compared to patients without cataplexy. Cataplexy remains a challenge for children and adults with narcolepsy and can interfere with daily activities. There is no cure for narcolepsy, but cataplexy can be well-managed with current and promising new treatment options on the horizon.

Patient-Reported Measures of Narcolepsy: The Need for Better Assessment

STUDY OBJECTIVES

Narcolepsy, a chronic disorder of the central nervous system, is clinically characterized by a symptom pentad that includes excessive daytime sleepiness, cataplexy, sleep paralysis, hypnopompic/hypnagogic hallucinations, and disrupted nighttime sleep. Ideally, screening and diagnosis instruments that assist physicians in evaluating a patient for type 1 or type 2 narcolepsy would be brief, easy for patients to understand and physicians to score, and would identify or rule out the need for electrophysiological testing.

METHODS

A search of the literature was conducted to review patient-reported measures used for the assessment of narcolepsy, mainly in clinical trials, with the goal of summarizing existing scales and identifying areas that may require additional screening questions and clinical practice scales.

RESULTS

Of the seven scales reviewed, the Epworth Sleepiness Scale continues to be an important outcome measure to screen adults for excessive daytime sleepiness, which may be associated with narcolepsy. Several narcolepsy-specific scales have demonstrated utility, such as the Ullanlinna Narcolepsy Scale, Swiss Narcolepsy Scale, and Narcolepsy Symptom Assessment Questionnaire, but further validation is required.

CONCLUSIONS

Although the narcolepsy-specific scales currently in use may identify type 1 narcolepsy, there are no validated questionnaires to identify type 2 narcolepsy. Thus, there remains a need for short, easily understood, and well-validated instruments that can be readily used in clinical practice to distinguish narcolepsy subtypes, as well as other hypersomnias, and for assessing symptoms of these conditions during treatment.

Update on the treatment of narcolepsy: clinical efficacy of pitolisant

Narcolepsy is a neurological disease that affects 1 in 2,000 individuals and is characterized by excessive daytime sleepiness (EDS). In 60-70% of individuals with narcolepsy, it is also characterized by cataplexy or a sudden loss of muscle tone that is triggered by positive or negative emotions. Narcolepsy decreases the quality of life of the afflicted individuals. Currently used drugs treat EDS alone (modafinil/armodafinil, methylphenidate, and amphetamine), cataplexy alone ("off-label" use of antidepressants), or both EDS and cataplexy (sodium oxybate). These drugs have abuse, tolerability, and adherence issues. A greater diversity of drug options is needed to treat narcolepsy. The small molecule drug, pitolisant, acts as an inverse agonist/antagonist at the H3 receptor, thus increasing histaminergic tone in the wake promoting system of the brain. Pitolisant has been studied in animal models of narcolepsy and used in clinical trials as a treatment for narcolepsy. A comprehensive search of online databases (eg, Medline, PubMed, EMBASE, the Cochrane Library Database, Ovid MEDLINE, Europe PubMed Central, EBSCOhost CINAHL, ProQuest Research Library, Google Scholar, and ClinicalTrials.gov) was performed. Nonrandomized and randomized studies were included. This review focuses on the outcomes of four clinical trials of pitolisant to treat narcolepsy. These four trials show that pitolisant is an effective drug to treat EDS and cataplexy in narcolepsy.

Spectral Analysis of Polysomnography in Narcolepsy

OBJECTIVE

This study was conducted to identify differences between people with narcolepsy and the normal control of delta and theta activity using electroencephalogram (EEG) spectrum analysis of nocturnal polysomnography (PSG).

METHODS

Seven narcolepsy patients and seven age-sex matched normal controls underwent PSG and multiple sleep latency tests. Participants' non-rapid eye movement (NREM) sleep EEGs in PSG was analyzed using a Fast Fourier Transform technique.

RESULTS

While NREM delta activity of people with narcolepsy declined during the first three periods of NREM, there was no change during the 4th period of NREM. The increase in NREM theta activity also lasted until the 3rd period of NREM but did not occur during the 4th period of NREM. In comparing sleep parameters, REM sleep latency in the narcolepsy group was significantly shorter than in controls.

CONCLUSION

These results suggest that people with narcolepsy are likely to have a delta and theta activity-related sleep disturbance mechanism in NREM sleep.

Exploring the presence of narcolepsy in patients with schizophrenia

BACKGROUND

There are several case reports of patients with narcolepsy and schizophrenia, but a systematic examination of the association of both disorders has not been done. The aim of this work is to assess the frequency of narcolepsy with cataplexy in a large consecutive series of adult patients with schizophrenia and schizoaffective disorder.

METHODS

We screened 366 consecutive patients with schizophrenia or schizoaffective disorder with a sleep questionnaire and the Epworth Sleepines scale (ESS) exploring narcoleptiform symptoms. Those who screened positive were assessed by a sleep specialist, and offered an HLA determination. CSF hypocretin-1 determination was proposed to those who were HLA DQB1*06:02 positive.

RESULTS

On the screening questionnaire, 17 patients had an ESS score ≥11 without cataplexy, 15 had cataplexy-like symptoms with an ESS score < 11, and four had an ESS score ≥11 plus cataplexy-like symptoms. Of those, 24 patients were evaluated by a sleep specialist. Five of these 24 were HLA DQB1*06:02 positive, and three of these five subjects underwent lumbar puncture showing normal hypocretin-1 levels.

CONCLUSIONS

Our results suggest that narcolepsy with cataplexy is not an unrecognized disease in adult patients with schizophrenia or schizoaffective disorder.

The utility of a 5(th) nap in multiple sleep latency test

BACKGROUND

This is the first study that aimed to look specifically at the utility of the 5(th) nap in the multiple sleep latency test (MSLT), a test used to assist in the diagnosis of narcolepsy.

METHODS

Data was retrospectively collected from the Sleep Disorders Centre of a Tertiary Hospital on patients that had a 5(th) nap during their MSLT from the 08(th) November 2011 to 12(th) November 2014.

RESULTS

Fifty-three patients had a 5(th) nap performed out of 378 MSLT studies. In 16% of cases a diagnosis of narcolepsy was given directly due to the inclusion of the 5(th) nap on the MSLT. Here a 5(th) nap allowed diagnostic criteria of mean sleep latency <8 minutes and >2 SOREMPS to be met. In 53% of cases the mean sleep latency increased due to 5(th) nap inclusion; the mean sleep latency of the first four naps was 5.6 vs. 6.7 after inclusion of the 5(th) nap.

CONCLUSIONS

The 5(th) nap is not often performed within the MSLT studies. Our study shows that only a few patients may benefit from a 5(th) nap opportunity which also led to increase of the mean sleep latency at the expense of extra time, cost, labour and increased patient anxiety.

Challenges in the development of therapeutics for narcolepsy

Narcolepsy is a neurological disorder that afflicts 1 in 2000 individuals and is characterized by excessive daytime sleepiness and cataplexy-a sudden loss of muscle tone triggered by positive emotions. Features of narcolepsy include dysregulation of arousal state boundaries as well as autonomic and metabolic disturbances. Disruption of neurotransmission through the hypocretin/orexin (Hcrt) system, usually by degeneration of the HCRT-producing neurons in the posterior hypothalamus, results in narcolepsy. The cause of Hcrt neurodegeneration is unknown but thought to be related to autoimmune processes. Current treatments for narcolepsy are symptomatic, including wake-promoting therapeutics that increase presynaptic dopamine release and anticataplectic agents that activate monoaminergic neurotransmission. Sodium oxybate is the only medication approved by the US Food and Drug Administration that alleviates both sleep/wake disturbances and cataplexy. Development of therapeutics for narcolepsy has been challenged by historical misunderstanding of the disease, its many disparate symptoms and, until recently, its unknown etiology. Animal models have been essential to elucidating the neuropathology underlying narcolepsy. These models have also aided understanding the neurobiology of the Hcrt system, mechanisms of cataplexy, and the pharmacology of narcolepsy medications. Transgenic rodent models will be critical in the development of novel therapeutics for the treatment of narcolepsy, particularly efforts directed to overcome challenges in the development of hypocretin replacement therapy.

H1N1 influenza virus induces narcolepsy-like sleep disruption and targets sleep-wake regulatory neurons in mice

An increased incidence in the sleep-disorder narcolepsy has been associated with the 2009-2010 pandemic of H1N1 influenza virus in China and with mass vaccination campaigns against influenza during the pandemic in Finland and Sweden. Pathogenetic mechanisms of narcolepsy have so far mainly focused on autoimmunity. We here tested an alternative working hypothesis involving a direct role of influenza virus infection in the pathogenesis of narcolepsy in susceptible subjects. We show that infection with H1N1 influenza virus in mice that lack B and T cells (Recombinant activating gene 1-deficient mice) can lead to narcoleptic-like sleep-wake fragmentation and sleep structure alterations. Interestingly, the infection targeted brainstem and hypothalamic neurons, including orexin/hypocretin-producing neurons that regulate sleep-wake stability and are affected in narcolepsy. Because changes occurred in the absence of adaptive autoimmune responses, the findings show that brain infections with H1N1 virus have the potential to cause per se narcoleptic-like sleep disruption.

Rapid eye movement and non-rapid eye movement sleep contributions in memory consolidation and resistance to retroactive interference for verbal material

STUDY OBJECTIVES

To test the hypothesis that rapid eye movement (REM) sleep contributes to the consolidation of new memories, whereas non-rapid eye movement (NREM) sleep contributes to the prevention of retroactive interference.

DESIGN

Randomized, crossover study.

SETTING

Two sessions of either a morning nap or wakefulness.

PARTICIPANTS

Twenty-five healthy young adults.

INTERVENTIONS

Declarative learning of word pairs followed by a nap or a wake interval, then learning of interfering word pairs and delayed recall of list A.

MEASUREMENTS AND RESULTS

After a restricted night (24:00-06:00), participants learned a list of word pairs (list A). They were then required to either take a nap or stay awake during 45 min, after which they learned a second list of word pairs (list B) and then had to recall list A. Fifty percent of word pairs in list B shared the first word with list A, resulting in interference. Ten subjects exhibited REM sleep whereas 13 subjects exhibited NREM stage 3 (N3) sleep. An interference effect was observed in the nap but not in the wake condition. In post-learning naps, N3 sleep was associated with a reduced interference effect, which was not the case for REM sleep. Moreover, participants exhibiting N3 sleep in the post-learning nap condition also showed a reduced interference effect in the wake condition, suggesting a higher protection ability against interference.

CONCLUSION

Our results partly support the hypothesis that non-rapid eye movement sleep contributes in protecting novel memories against interference. However, rapid eye movement sleep-related consolidation is not evidenced.

Disrupted nighttime sleep in narcolepsy

STUDY OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Use of PCR with sequence-specific primers for high-resolution human leukocyte antigen typing of patients with narcolepsy

Background

Narcolepsy is a neurologic disorder characterized by excessive daytime sleepiness, symptoms of abnormal rapid eye movement (REM) sleep, and a strong association with HLA-DRB1^*1501, -DQA1^*0102, and -DQB1^*0602. Here, we investigated the clinico-physical characteristics of Korean patients with narcolepsy, their HLA types, and the clinical utility of high-resolution PCR with sequence-specific primers (PCR-SSP) as a simple typing method for identifying DRB1^*15/16, DQA1, and DQB1 alleles.

Methods

The study population consisted of 67 consecutively enrolled patients having unexplained daytime sleepiness and diagnosed narcolepsy based on clinical and neurological findings. Clinical data and the results of the multiple sleep latency test and polysomnography were reviewed, and HLA typing was performed using both high-resolution PCR-SSP and sequence-based typing (SBT).

Results

The 44 narcolepsy patients with cataplexy displayed significantly higher frequencies of DRB1^*1501 (Pc= 0.003), DQA1^*0102 (Pc=0.001), and DQB1^*0602 (Pc=0.014) than the patients without cataplexy. Among patients carrying DRB1^*1501-DQB1^*0602 or DQA1^*0102, the frequencies of a mean REM sleep latency of less than 20 min in nocturnal polysomnography and clinical findings, including sleep paralysis and hypnagogic hallucination were significantly higher. SBT and PCR-SSP showed 100% concordance for high-resolution typing of DRB1^*15/16 alleles and DQA1 and DQB1 loci.

Conclusions

The clinical characteristics and somnographic findings of narcolepsy patients were associated with specific HLA alleles, including DRB1^*1501, DQA1^*0102, and DQB1^*0602. Application of high-resolution PCR-SSP, a reliable and simple method, for both allele- and locus-specific HLA typing of DRB1^*15/16, DQA1, and DQB1 would be useful for characterizing clinical status among subjects with narcolepsy.

Complex movement disorders at disease onset in childhood narcolepsy with cataplexy

Narcolepsy with cataplexy is characterized by daytime sleepiness, cataplexy (sudden loss of bilateral muscle tone triggered by emotions), sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep. Narcolepsy with cataplexy is most often associated with human leucocyte antigen-DQB1*0602 and is caused by the loss of hypocretin-producing neurons in the hypothalamus of likely autoimmune aetiology. Noting that children with narcolepsy often display complex abnormal motor behaviours close to disease onset that do not meet the classical definition of cataplexy, we systematically analysed motor features in 39 children with narcolepsy with cataplexy in comparison with 25 age- and sex-matched healthy controls. We found that patients with narcolepsy with cataplexy displayed a complex array of ‘negative’ (hypotonia) and ‘active’ (ranging from perioral movements to dyskinetic–dystonic movements or stereotypies) motor disturbances. ‘Active’ and ‘negative’ motor scores correlated positively with the presence of hypotonic features at neurological examination and negatively with disease duration, whereas ‘negative’ motor scores also correlated negatively with age at disease onset. These observations suggest that paediatric narcolepsy with cataplexy often co-occurs with a complex movement disorder at disease onset, a phenomenon that may vanish later in the course of the disease. Further studies are warranted to assess clinical course and whether the associated movement disorder is also caused by hypocretin deficiency or by additional neurochemical abnormalities.

Cyclic alternating pattern in narcolepsy patients and healthy controls after partial and total sleep deprivation

OBJECTIVE

To investigate the regulation NREM sleep at baseline and in morning recovery sleep after partial and total sleep deprivation (SD) in narcolepsy-cataplexy (NC) using cyclic alternating pattern (CAP).

METHODS

Daytime sleep under either increased (no sleep in the previous night) or decreased sleep pressure (allowing 4h of sleep, 23:00-3:00 h) was recorded in ten drug-free, HLA-positive, hypocretin deficient NC patients and ten age, gender and body mass index matched healthy controls. Baseline sleep was also recorded and used for comparison purposes. CAP parameters were scored and analyzed for each subject.

RESULTS

Narcolepsy patients had significantly lower CAP rate, CAP index, CAP time, number of CAP cycles, A1 index and number of A1 cycles in comparison to healthy controls at baseline as well as after partial and total SD. In both narcolepsy patients and healthy control subjects there was a significant decrease in these parameters after partial and total SD but the changes followed a similar pattern.

CONCLUSION

The persistence of baseline differences in CAP parameters between narcolepsy patients and healthy controls and their similar behavior after partial and total SD suggests similar homeostatic NREM sleep regulation but on a different level.

SIGNIFICANCE

CAP analysis demonstrates that NREM sleep homeostasis although altered, is functional in narcolepsy patients.

Orexin/hypocretin plays a role in the response to physiological disequilibrium

In the decade since the discovery that pathology of the orexin/hypocretin system is causative for the sleep disorder narcolepsy, considerable progress has been made in understanding the functional role of the neuropeptide. Two, apparently separate functions of orexin have emerged as a consensus from studies to date. The first is the effect on vigilance state boundaries, as exemplified by narcolepsy. Thus the absence of orexin severely limits the ability to maintain prolonged periods of wakefulness or sleep and also allows the unregulated appearance of cataplexy as sudden muscle weakness during wakefulness. The second function is that orexin acts as a signaling molecule in transferring information about physiological disequilibrium to the central nervous system. Orexin activates the central arousal and motor systems during such disequilibrium and so may facilitate the necessary response and adaptation to restore equilibrium. A feasible relationship between these two functions is therefore that the maintenance of prolonged and active wakefulness is an integral part of this adaptive process. Furthermore, the limit placed on the onset of sleep by orexin suggests that these adaptive processes then continue during sleep to become integrated into the development of a coping strategy for the longer term.

Hypocretin/Orexin neuropeptides: participation in the control of sleep-wakefulness cycle and energy homeostasis

Hypocretins or orexins (Hcrt/Orx) are hypothalamic neuropeptides that are synthesized by neurons located mainly in the perifornical area of the posterolateral hypothalamus. These hypothalamic neurons are the origin of an extensive and divergent projection system innervating numerous structures of the central nervous system. In recent years it has become clear that these neuropeptides are involved in the regulation of many organic functions, such as feeding, thermoregulation and neuroendocrine and cardiovascular control, as well as in the control of the sleep-wakefulness cycle. In this respect, Hcrt/Orx activate two subtypes of G protein-coupled receptors (Hcrt/Orx1R and Hcrt/Orx2R) that show a partly segregated and prominent distribution in neural structures involved in sleep-wakefulness regulation. Wakefulness-enhancing and/or sleep-suppressing actions of Hcrt/Orx have been reported in specific areas of the brainstem. Moreover, presently there are animal models of human narcolepsy consisting in modifications of Hcrt/Orx receptors or absence of these peptides. This strongly suggests that narcolepsy is the direct consequence of a hypofunction of the Hcrt/Orx system, which is most likely due to Hcrt/Orx neurons degeneration.

The main focus of this review is to update and illustrate the available data on the actions of Hcrt/Orx neuropeptides with special interest in their participation in the control of the sleep-wakefulness cycle and the regulation of energy homeostasis. Current pharmacological treatment of narcolepsy is also discussed.

Advances in narcolepsy

Narcolepsy with cataplexy is a rare but life-long and challenging disorder. Current insight into the pathophysiology of this condition seems to be autoimmune-mediated postnatal cell death of hypocretin neurons occurring by organ-specific autoimmune targeting with HLA-T-cell receptor interactions. The hypocretin system seems to have an influence on multiple organ systems beyond its wake-promoting mechanisms. The recent availability of cerebrospinal fluid hypocretin-1 analysis has led to definitive diagnostic criteria for narcolepsy with cataplexy. Pharmacologic first-line treatments for excessive daytime sleepiness and cataplexy is sodium oxybate, with modafinil for daytime sleepiness, in adults and children. Other investigative agents and treatment modalities hold promise in future directions for narcolepsy.

Narcolepsy: autoimmunity, effector T cell activation due to infection, or T cell independent, major histocompatibility complex class II induced neuronal loss?

Human narcolepsy with cataplexy is a neurological disorder, which develops due to a deficiency in hypocretin producing neurons in the hypothalamus. There is a strong association with human leucocyte antigens HLA-DR2 and HLA-DQB1*0602. The disease typically starts in adolescence. Recent developments in narcolepsy research support the hypothesis of narcolepsy being an immune-mediated disease. Narcolepsy is associated with polymorphisms of the genes encoding T cell receptor alpha chain, tumour necrosis factor alpha and tumour necrosis factor receptor II. Moreover the rate of streptococcal infection is increased at onset of narcolepsy. The hallmarks of anti-self reactions in the tissue--namely upregulation of major histocompatibility antigens and lymphocyte infiltrates--are missing in the hypothalamus. These findings are questionable because they were obtained by analyses performed many years after onset of disease. In some patients with narcolepsy autoantibodies to Tribbles homolog 2, which is expressed by hypocretin neurons, have been detected recently. Immune-mediated destruction of hypocretin producing neurons may be mediated by microglia/macrophages that become activated either by autoantigen specific CD4(+) T cells or superantigen stimulated CD8(+) T cells, or independent of T cells by activation of DQB1*0602 signalling. Activation of microglia and macrophages may lead to the release of neurotoxic molecules such as quinolinic acid, which has been shown to cause selective destruction of hypocretin neurons in the hypothalamus.

Behavioural and neurophysiological correlates of human cataplexy: a video-polygraphic study

OBJECTIVES

To investigate the behavioural and neurophysiological pattern of cataplexy.

METHODS

Seven narcolepsy with cataplexy patients underwent daytime videopolygraphy using humorous movies or/and jokes to trigger cataplectic attacks.

RESULTS

During segmental cataplectic attacks, EMG showed brief and irregular periods of silencing focally involving facial, neck, axial or limb muscles, sometimes coinciding with bursts of rapid eye movements. All patients enacted intentional movements in response to these segmental postural lapses. During global cataplectic attacks, EMG showed suppression of activity alternated with patterned enhancement, enhanced EMG activity in neck muscles preceding that of other cranial, axial and lower limb muscles. This waxing and waning EMG pattern ended with a complete body collapse and persistent muscle atonia. Breathing irregularities, heart rate (HR) instability and EEG desynchronization were observed during global cataplectic attacks without any appreciable blood pressure changes, but with HR deceleration and silencing of sympathetic skin response while in complete atonia. Patients subjectively perceived the involuntary postural lapses as startling and alarming.

CONCLUSIONS

Cataplexy in our patients showed many of the features of tonic REM sleep.

SIGNIFICANCE

Cataplexy can be construed as a "freezing-like" perturbation of the orienting response with transient impairment of posture and movements resulting in a "patchwork-compromise-behaviour".

Evidence for metabolic hypothalamo-amygdala dysfunction in narcolepsy

STUDY OBJECTIVES

Proton resonance spectroscopy (1H-MRS) allows noninvasive chemical tissue analysis in the living brain. As neuronal loss and gliosis have been described in narcolepsy, metabolites of primary interest are N-acetylaspartate (NAA), a marker of neuronal integrity and myo-Inositol (ml), a glial marker and second messenger involved in the regulation of intracellular calcium. One 1H-MRS study in narcolepsy found no metabolic changes in the pontomedullary junction. Another study showed a reduction in NAA/creatine-phosphocreatine (Cr) in the hypothalamus of narcolepsy patients with cataplexy. We aimed to test for metabolic changes in specific brain areas, "regions of interest," thought to be involved in emotional processing, sleep regulation and pathophysiology of narcolepsy: hypothalamus, pontomesencephalic junction and both amygdalae.

DESIGN

We performed 1H-MRS using a 3T Philips Achieva whole body MR scanner. Single-voxel proton MR spectra were acquired and quantified with LCModel to determine metabolite concentration ratios.

SETTING

The participants in the study were recruited at the outpatient clinic for sleep medicine, Department of Neurology and magnetic resonance spectroscopy was performed at the MRI facility, University Hospital Zurich.

PARTICIPANTS

1H-MRS was performed in fourteen narcolepsy patients with cataplexy, CSF hypocretin deficiency (10/10) and HLA-DQB1*0602 positivity (14/14) and 14 age, gender and body mass index matched controls. Patients were treatment naïve or off therapy for at least 14 days before scanning.

MEASUREMENTS AND RESULTS

No differences were observed in the regions of interest for (total NAA)/Cr ratios. Myo-Inositol (ml)/Cr was significantly lower in the right amygdala of the patients, compared to controls (P < 0.042). Significant negative correlations only in the patients group were found between (total NAA)/Cr in hypothalamus and ml/Cr in the right amygdala (r = -0.89, P < 0.001), between ml/Cr in hypothalamus and (total NAA)/Cr in the right amygdala (r = -63, P < 0.05) and between ml/Cr in the left amygdala and total NAA)/Cr in the pontomesencephalic junction (r = -0.69, P < 0.05).

CONCLUSION

Our findings suggest amygdala involvement and possible hypothalamo-amygdala dysfunction in narcolepsy.

Narcolepsy--master of disguise: evidence-based recommendations for management

Narcolepsy is a neurological disorder affecting the regulation of sleep and wakefulness. It is characterized by excessive daytime sleepiness, cataplexy, and other rapid eye movement (REM) sleep-associated manifestations (eg, hypnagogic hallucinations and sleep paralysis). The recognition of this disorder is usually delayed by 10 to 15 years, largely because of its protean manifestations, insidious nature, and lack of physician awareness. Delayed diagnosis is associated with poor quality of life, depression, and increased likelihood of accidents. Health care providers should include narcolepsy in the differential diagnosis of patients with excessive sleepiness, chronic fatigue, sleep-disordered breathing, depression, and attention-deficit/hyperactivity disorder. Narcolepsy is a lifelong disorder that often requires pharmacological treatments, which may include wake-promoting stimulants for excessive sleepiness and gamma-hydroxybutyrate (sodium oxybate) and antidepressants for REM sleep-associated manifestations. This article presents a case of a 47-year-old man with long-standing sleepiness and cataplexy who was eventually diagnosed with narcolepsy 30 years after the first onset of symptoms. The presenting manifestations of narcolepsy, diagnostic criteria, and its management are also discussed.

Weak with sex: sexual intercourse as a trigger for cataplexy

INTRODUCTION

Sudden, often positive emotions are typical triggers for cataplexy in patients with narcolepsy-cataplexy (NC). Cataplexy during sexual intercourse and orgasm (orgasmolepsy) has been previously reported, but its frequency and characteristics are poorly known.

AIM

To assess frequency and features of loss of muscle tone during sexual intercourse in a series of patients with NC, other sleep-wake disorders, and healthy controls.

METHODS

Review of sleep questionnaires (including the Stanford Cataplexy Questionnaire) of 75 subjects (29 with NC, 26 with other sleep-wake disorders, and 20 healthy controls), followed by an interview with specific focus on muscle loss during sexual activity in suspicious cases.

MAIN OUTCOME MEASURES

Cataplexy during sexual intercourse and orgasm (orgasmolepsy).

RESULTS

Orgasmolepsy was reported by three NC patients (two female, one male), one male patient with behaviorally induced insufficient sleep syndrome (BIISS) and cataplexy-like symptoms, and none of the healthy controls. In the two female NC patients, orgasmolepsy occurred by each sexual intercourse, and the male patient reported orgasmolepsy only when in a relationship involving emotional commitment and trust. In the patient with BIISS and orgasmolepsy, cataplexy-like symptoms involved unilaterally upper or lower limbs in association with negative emotions or sports activities.

CONCLUSIONS

Cataplexy during sexual intercourse is a distinct feature of NC, which can, however, be reported rarely also by patients with other sleep-wake disorders. Insufficient arousal may favor the occurrence of cataplexy and cataplexy-like symptoms, including orgasmolepsy. Hypocretin deficiency and reward dysregulation in narcolepsy may further facilitate this phenomenon and contribute to its repetitive occurrence.

Potential adverse effects of amphetamine treatment on brain and behavior: a review

Amphetamine stimulants have been used medically since early in the twentieth century, but they have a high abuse potential and can be neurotoxic. Although they have long been used effectively to treat attention deficit hyperactivity disorder (ADHD) in children and adolescents, amphetamines are now being prescribed increasingly as maintenance therapy for ADHD and narcolepsy in adults, considerably extending the period of potential exposure. Effects of prolonged stimulant treatment have not been fully explored, and understanding such effects is a research priority. Because the pharmacokinetics of amphetamines differ between children and adults, reevaluation of the potential for adverse effects of chronic treatment of adults is essential. Despite information on the effects of stimulants in laboratory animals, profound species differences in susceptibility to stimulant-induced neurotoxicity underscore the need for systematic studies of prolonged human exposure. Early amphetamine treatment has been linked to slowing in height and weight growth in some children. Because the number of prescriptions for amphetamines has increased several fold over the past decade, an amphetamine-containing formulation is the most commonly prescribed stimulant in North America, and it is noteworthy that amphetamines are also the most abused prescription medications. Although early treatment does not increase risk for substance abuse, few studies have tracked the compliance and usage profiles of individuals who began amphetamine treatment as adults. Overall, there is concern about risk for slowed growth in young patients who are dosed continuously, and for substance abuse in patients first medicated in late adolescence or adulthood. Although most adult patients also use amphetamines effectively and safely, occasional case reports indicate that prescription use can produce marked psychological adverse events, including stimulant-induced psychosis. Assessments of central toxicity and adverse psychological effects during late adulthood and senescence of adults who receive prolonged courses of amphetamine treatment are warranted. Finally, identification of the biological factors that confer risk and those that offer protection is also needed to better specify the parameters of safe, long-term, therapeutic administration of amphetamines to adults.

Challenging sleep homeostasis in narcolepsy-cataplexy: implications for non-REM and REM sleep regulation

STUDY OBJECTIVES

We recently proposed insufficient non-rapid eye movement sleep (NREMS) intensity to contribute to disturbed nocturnal sleep in patients with narcolepsy-cataplexy (NC). To test this hypothesis, we investigated the effect of physiologically intensified NREMS in recovery sleep following sleep deprivation.

DESIGN

Nocturnal baseline and recovery sleep architecture, and the sleep electroencephalogram (EEG) before and after 40 hours of sustained wakefulness were compared between 6 drug-free patients with NC (age range: 19-37 years) and 6 individually matched, healthy control subjects (18-43 years).

MEASUREMENTS

Sleep and sleep EEG power spectra (C3A2 derivation). The dynamics of the homeostatic Process S were estimated from the time course of slow-wave activity (SWA, spectral power within 0.75-4.5 Hz) across consecutive NREMS episodes.

SETTINGS

Sleep research laboratory.

RESULTS

In baseline, SWA decreased across consecutive NREMS episodes in patients with NC and control subjects. The build-up of SWA, however, was attenuated in NC in the second episode (P = 0.01) due to a higher number of short wake periods (P = 0.02). Prolonged wakefulness increased initial SWA in both groups (P = 0.003) and normalized the baseline differences between patients and control subjects in the time course of SWA in NREMS. The changed dynamics of SWA in the patients in recovery sleep when compared with baseline were associated with reduced numbers of intermittent wake periods in the first (P = 0.01) and second (P = 0.04) NREMS episodes. All patients, but no control subjects, showed a sleep-onset rapid eye movement period (SOREMP) in both baseline and recovery sleep. Sleep deprivation increased SOREMP duration (P = 0.03).

CONCLUSIONS

Increased SWA after sleep deprivation indicates that sleep homeostasis is functional in NC. Increased NREMS intensity in recovery sleep postpones sleep fragmentation, supporting our concept that sleep fragmentation is directly related to insufficient NREMS intensity in NC. The persistence of SOREMP despite enhanced NREMS pressure suggests an abnormal interaction between NREMS and REMS regulatory processes.

Association of narcolepsy-cataplexy with HLA-DRB1 and DQB1 in Mexican patients: a relationship between HLA and gender is suggested

Background

Narcolepsy-cataplexy is characterized by excessive daytime sleepiness with recurrent episodes of irresistible sleep, cataplexy, hallucinations and sleep paralysis. Its aetiology is unknown, but it is positively associated with the human leukocyte antigens (HLA) in all studied populations. The purpose of the present study was to investigate the association of HLA class II DRB1/DQB1 alleles with narcolepsy-cataplexy in Mexican Mestizo patients.

Methods

This is a case-control study of consecutive patients and ethnically matched controls. We included 32 patients diagnosed with typical narcolepsy-cataplexy, of the National Institute of Neurology, of the Institute of Psychiatry and at the Center of Narcolepsy at Stanford University. As healthy controls, 203 Mexican Mestizos were included. DRB1 alleles were identified using sequence based typing. A PCR-SSOP reverse dot blot was used for DQB1 typing. Allele frequency was calculated by direct counting and the significance of the differences was assessed using the Yates Chi square. Odds ratio and confidence intervals were evaluated.

Results

HLA-DRB1*1501 (OR = 8.2; pc < 0.0001) and DQB1*0602 (OR = 8.4; pc < 0.0001) were found positively associated with narcolepsy. When deleting DQB1*0602+ patients from the analysis, DQB1*0301 was also found increased (OR = 2.7; p = 0.035; pc = NS). DQB1*0602/DQB1*0301 genotype was present in 15.6% of the cases (OR = 11.5; p = 0.00035), conferring a high risk. DRB1*0407 (OR = 0.2; p = 0.016 pc = NS) and DQB1*0302(OR = 0.4; p = 0.017, pc = NS) were found decreased in the patients. The gender stratification analysis showed a higher risk in females carrying DRB1*1501 (OR = 15.8, pc < 0.0001) and DQB1*0602 (OR = 19.8, pc < 0.0001) than in males (OR = 5.0 for both alleles; p = 0.012, pc = NS for DRB1 & p = 0.0012, pc = 0.017 for DQB1). The susceptibility alleles found in Mexicans with narcolepsy are also present in Japanese and Caucasians; DRB1*04 linked protection has also been shown in Koreans. A stronger HLA association is suggested in females, in accordance with the sexual dimorphism claimed previously.

Conclusion

This knowledge may contribute to a better understanding of the disease pathogenesis in different populations. The evaluation of the risk to develop narcolepsy-cataplexy in carriers of the described alleles/genotypes may also be possible. A larger sample should be analysed in Mexican and in other Hispanic patients to confirm these results.

Management of narcolepsy

BACKGROUND

Narcolepsy is a rare chronic sleep disorder classically characterized by excessive daytime sleepiness. Other symptoms of the disease, including cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep, may follow later. The disease can be incapacitating and frequently results in impaired psychosocial interaction. In the absence of a cure for narcolepsy, medical therapy is directed at symptom control.

OBJECTIVES

The aim of this study was to review the current approach to the treatment of narcolepsy.

METHODS

A search of three bibliographic databases (MEDLINE/PubMed, EMBASE and the Cochrane Library Database) was conducted from 1966 to January 2008 using the National Library of Medicine MeSH search terms narcolepsy and cataplexy. Relevant studies, case reports, review articles, editorials, short communications and chapters from selected textbooks were then extracted and manually cross-referenced.

RESULTS/CONCLUSIONS

Traditionally, stimulants have been used to improve the symptoms of excessive daytime sleepiness. However, the treatment of narcolepsy has evolved recently with the widespread use of newer drugs, including modafinil for daytime sleepiness, newer antidepressants for cataplexy and gamma-hydroxybutyrate (sodium oxybate) for both excessive daytime sleepiness and cataplexy.

Clinical, behavioural and polysomnographic correlates of cataplexy in patients with narcolepsy/cataplexy

BACKGROUND

Cataplexy is the main motor symptom of narcolepsy/cataplexy and is considered a form of rapid eye movement (REM) sleep motor dyscontrol appearing during wakefulness and elicited by emotions. This study examined the relationship between the frequency of cataplectic attacks in patients with narcolepsy/cataplexy and (a) the clinical and behavioural characteristics of cataplectic attacks, including the emotional tone of trigger events, and (b) the polysomnographic characteristics of daytime sleepiness, nocturnal sleep structure and indices of motor disorders during sleep.

METHODS

A consecutive series of 44 first-diagnosed drug-naive patients with narcolepsy/cataplexy, fulfilling the International Classification of Sleep Disorders, 2nd edition (ICSD-2) clinical and polysomnographic diagnostic criteria, were interviewed to estimate the frequency and clinical characteristics of cataplectic attacks and the occurrence of REM sleep behaviour disorder (RBD). All patients also underwent a video-polysomnographic recording to assess their sleep parameters and indices of altered motor control during sleep.

RESULTS

Patients were divided into two groups on the basis of the frequency of cataplectic attacks, namely high-frequency (n=30) or low-frequency (n=14) depending on whether they estimated they had more or less than one attack per month. High-frequency patients (with a larger proportion of men) reported attacks more often affecting mainly the head, jaw and shoulder muscles and experienced more events among those listed as possible triggers of attacks. Sixty-one percent of patients reported RBD and 43% had an RBD episode at video-polysomnography regardless of the frequency of cataplectic attacks or gender. Lastly, the frequency of periodic leg movements (PLM) per hour was higher in men than women and increased with age.

CONCLUSIONS

Patients with more than one cataplectic attack per month had more frequent involvement of head, jaw and shoulder muscles and were mainly men. The proportions of patients with clinically assessed RBD and an RBD episode documented by video-polysomnography, as well as conspicuous values of PLM per hour, are fairly consistent with those reported in recent small-group studies. Therefore, it seems legitimate to argue that RBD and PLM are nocturnal manifestations intrinsic to narcolepsy/cataplexy and that the gender-related differences in the frequency of attacks and the value of PLM per hour may be indicative of a larger difference in the clinical and polysomnographic characteristics of narcolepsy/cataplexy than hitherto suspected.

Screening the human prepro-orexin gene in a single-centre narcolepsy cohort

BACKGROUND AND PURPOSE

Although the orexin system has an established role in narcolepsy, the mechanism of orexin deficiency in human cases is unknown. The strong association with human leukocyte antigen (HLA) DQB1*0602 suggests an autoimmune basis, but supporting evidence is lacking. Although data indicate that HLA status is not the sole genetic factor, only a single case of a functional orexin system mutation has been discovered, in a study with a selection bias designed to increase yield. In this study, we examined the prepro-orexin gene for mutations in a cohort of unrelated patients with narcolepsy from a national UK referral centre.

PATIENTS AND METHODS

Subjects with a diagnosis of narcolepsy were recruited from a patient database. DNA samples were obtained using buccal smear kits. The prepro-orexin gene was amplified using polymerase chain reactions and screened for polymorphisms and mutations.

RESULTS

Eighty-one patients were recruited, of whom 69 provided DNA samples. A previously described intronic single nucleotide polymorphism, of unlikely significance, was identified in one subject who had typical clinical and electrophysiological features of narcolepsy. It was located 16 base pairs downstream from exon 1. No other mutations were found.

CONCLUSION

This result supports existing evidence which indicates that mutations of the prepro-orexin gene are rare and that the genetic contribution to the aetiology of human narcolepsy is likely to be complex.

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.

HLA-DQB1 allele and hypocretin in Korean narcoleptics with cataplexy

Cataplexy is one of the most pathognomonic symptoms in narcolepsy. This study was designed to investigate the frequency of the HLA-DQB1 allele and cerebrospinal fluid (CSF) hypocretin levels in Korean narcoleptics with cataplexy as compared with those who do not have cataplexy. Seventy-two narcoleptics were selected based on polysomnography and multiple sleep latency test as well as their history and clinical symptoms at Sleep Disorders Clinic. The patients were divided into a narcolepsy with cataplexy group (n=56) and a narcolepsy without cataplexy group (n=16). All patients were subjected to HLA typing to determine the frequency of DQB1 allele and to spinal tapping to measure the level of CSF hypocretin. In cataplexy-positive patients, as compared with cataplexy-negative patients, the frequency of HLA-DQB1*0602 was found to be significantly high (89.3% vs. 50.0%) (p=0.003). On the other hand, the frequency of HLA-DQB1*0601 was found to be significantly low (0% vs. 43.8%) (p<0.001). In 48 of 56 cataplexy-positive patients (85.7 %), hypocretin levels were decreased (<or=110 pg/mL). However, only 6 of 16 cataplexy-negative patients (37.5%) exhibited a decreased hyopcretin level (p<0.001). The high frequency of HLA-DQB1*0602, low frequency of HLA-DQB1*0601 and low hypocretin levels in cataplexy-positive groups suggest that cataplexy-positive narcolepsy might be an etiologically different disease entity from the cataplexy-negative.

Association of HLA-DR and -DQ genes with narcolepsy in Koreans: comparison with two control groups, randomly selected subjects and DRB1*1501-DQB1*0602--positive subjects

The purpose of this study was to investigate the association of human leukocyte antigen (HLA) class II alleles with narcolepsy-cataplexy susceptibility in Koreans. The distribution of HLA-DRB1 and -DQB1 alleles and presence or absence of DRB3/4/5 alleles were examined in 60 narcoleptic patients with clear-cut cataplexy, and the results were compared with two groups of healthy controls: 200 randomly selected controls and 144 DRB1*1501-DQB1*0602 positive controls. All of the narcoleptic patients were DRB1*1501 and DQB1*0602 positive, and their frequencies were significantly higher in patients than in random controls (100% vs 17.0%, p(c) = 2.3 x 10(-30), OR = 583.96; 100% vs 16.5%, p(c) = 3.9 x 10(-31), OR = 605.00). The HLA association in Koreans was as tight as that reported in Japanese. Several DRB1 (*0101, *0405, *0901) and DQB1 alleles (*0303, *0401, *0501, *0601, *0604) were found to have weak protective effects against narcolepsy. DRB4 showed strong protective effect, and this was also significant when compared with DRB1*1501-DQB1*0602 positive controls (18.3% vs 44.4%, p(c) = 0.001, OR = 0.28). DRB3 (OR = 1.86) and DQB1*0301 (OR = 2.45) were found to have weak predisposing effect, when compared with DRB1*1501-DQB1*0602 positive controls. The protective effect of DRB4 has to be further studied in other populations.

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.

Further evidence supporting the use of sodium oxybate for the treatment of cataplexy: a double-blind, placebo-controlled study in 228 patients

BACKGROUND AND PURPOSE

To measure the effect of the nocturnal administration of sodium oxybate on cataplexy in patients with narcolepsy.

PATIENTS AND METHODS

This trial was conducted with 228 adult narcolepsy/cataplexy patients in 42 sleep clinics. Patients using anticataplectic medications were weaned from these medications, then randomized to receive 4.5, 6 or 9 g sodium oxybate nightly or placebo for 8 weeks. Patients receiving 6 and 9 g doses were titrated to their final dose in weekly 1.5 g increments. Placebo patients underwent a randomized mock dose-titration schedule. The effect of sodium oxybate on weekly cataplexy attacks was measured using patient daily diaries.

RESULTS

Compared to placebo, nightly doses of 4.5, 6 and 9 g sodium oxybate for 8 weeks resulted in statistically significant median decreases in weekly cataplexy attacks of 57.0, 65.0 and 84.7%, respectively. The decrease in cataplexy at the 4.5 g dose represents a novel finding. The weekly increase in sodium oxybate dose was associated with fewer adverse events than previously reported in double-blind sodium oxybate trials using fixed doses. Some adverse events reported demonstrated a clear dose-response relationship.

CONCLUSIONS

In the largest study of its kind, sodium oxybate was highly effective for the treatment of cataplexy. The improvements in cataplexy are dependent on the dosage of sodium oxybate as well on the duration of treatment. Weekly dose titration appears to be well-tolerated.

Insights from studying human sleep disorders

Problems with sleep are one of the commonest reasons for seeking medical attention. Knowledge gained from basic research into sleep in animals has led to marked advances in the understanding of human sleep, with important diagnostic and therapeutic implications. At the same time, research guided by human sleep disorders is leading to important basic sleep concepts. For example, sleep may not be a global, but rather a local, brain phenomenon. Furthermore, contrary to common assumptions, wakefulness, rapid eye movement (REM) and non-REM sleep are not mutually exclusive states. This striking realization explains a fascinating range of clinical phenomena.

Modafinil: a novel stimulant for the treatment of narcolepsy

Excessive daytime sleepiness (EDS) is a common and debilitating symptom of narcolepsy and other sleep disorders. Modafinil is a novel stimulant which effectively treats EDS, yet lacks many of the undesirable side-effects commonly encountered with currently available compounds. The specific mode of action of modafinil is not well understood, but it may promote sleep by indirectly influencing adrenergic or GABAergic neurotransmission. Modafinil-induced wakefulness is not associated with rebound hypersomnolence or the potential for abuse as is often encountered with other stimulants such as amphetamines. At typical therapeutic doses, modafinil may produce dry mouth but generally has a low incidence of minor side-effects. Many preclinical and clinical studies have demonstrated the effectiveness of modafinil in promoting wakefulness and vigilance in normal subjects and in those with EDS. Modafinil significantly improves the EDS of narcolepsy and also may improve the EDS of idiopathic hypersomnia and obstructive sleep apnoea. Modafinil's low prevalence of side-effects, minimal potential for abuse, and lack of rebound hypersomnia indicate that it has potential to become a widely prescribed drug for the treatment of narcolepsy.

Medications for the treatment of narcolepsy

Narcolepsy is a syndrome of unknown aetiology characterised by excessive daytime sleepiness (often severe) usually in association with cataplexy (brief episodes of partial or complete muscle paralysis) and often with other uncommon symptoms. Due to limited disease-specific knowledge, medication treatment for this condition has focussed on specific symptom amelioration rather than improving or eliminating underlying disease mechanisms. Such treatment generally consists of stimulants for daytime sleepiness and anticataplectic medication for cataplexy; hence, both types of agents are reviewed in this article. Recent discoveries, including the finding that canine familial narcolepsy is caused by a single gene defect in the hypocretin receptor, coupled with the findings in human narcoleptics of undetectable hypocretin levels in the CSF and of severe hypocretin-containing neuronal atrophy in brains of deceased narcoleptics, have shifted the focus of narcolepsy treatment research to the hypocretin system. The hope is that a single agent can be developed to provide effective treatment for all symptoms of narcolepsy. While the mechanism of action in narcolepsy is unknown, gamma-hydroxybutyrate (GHB) is proving to be such an agent. Interestingly, GHB is not known to impact hypocretin pathways in the brain, yet specific research exploring this possible interaction has not been performed. The market for medications limited to use by narcoleptics is small because of the relatively low prevalence of narcolepsy; however, the prevalence of clinically important daytime sleepiness and/or fatigue is surprisingly high. New agents that effectively manage the sleepiness of narcolepsy thus have a much larger potential for appropriate use in treating sleepiness and fatigue in the general population. This fact has recently been demonstrated by the tremendous success of modafinil, a drug introduced to the market a little over 2 years ago, which was developed to treat sleepiness in narcolepsy but now is used in a much larger patient population.