Pharmacotherapy for cataplexy

Clinical Evaluation and Management of Narcolepsy in Children and Adolescents

While sleepiness is common among children, and particularly adolescents, profound sleepiness in the setting of apparently adequate sleep should prompt consideration of a central disorder of hypersomnolence. These disorders, which include narcolepsy, idiopathic hypersomnia, Kleine-Levin syndrome, and others, are likely underrecognized in the pediatric population. Narcolepsy in particular should be of interest to child neurologists as the unique signs and symptoms of this disease often prompt evaluation in pediatric neurology clinics. While sleepiness may appear to be a straightforward complaint, its evaluation requires a nuanced approach. Cataplexy, a hallmark of narcolepsy, can be confused for other neurologic conditions, though understanding its various manifestations makes it readily identifiable. Clinicians should be aware of these symptoms, as delay in diagnosis and misdiagnosis are common in childhood narcolepsy. While treatment options have been limited in the past, many new therapeutic options have become available and can result in significant improvement in symptoms. Given the age at presentation, paroxysmal and chronic features, diagnostic modalities, and available treatment options, the field of child neurology is well equipped to see patients with narcolepsy. In this review, I will focus on the presentation, evaluation, and management of pediatric patients with narcolepsy.

Narcolepsy Treatment: Voices of Adolescents

INTRODUCTION

Narcolepsy, characterized by excessive daytime sleepiness, is a debilitating lifelong sleep disorder for which there is no cure. Current pharmacological and nonpharmacological treatments directed toward symptom management may be suboptimal. This qualitative study explores the perspective of adolescents on therapeutic interventions for narcolepsy.

METHODS

Semi-structured interviews with adolescents with narcolepsy were conducted from May to August 2019 at The Hospital for Sick Children in Toronto, Canada. Qualitative thematic analysis was utilized to generate themes emerging from the data.

RESULTS

Eighteen adolescents with narcolepsy (age range = 10-17, mean age = 14.4 ± 2.0 years, 72% male) participated and 56% had cataplexy. Four prominent themes arose regarding therapeutic interventions for narcolepsy. Firstly, participants described that pharmacotherapy was moderately effective but did not fully relieve symptoms associated with narcolepsy. Secondly, while medications are the first line treatment for narcolepsy, many participants reported frustration regarding medication dependence and side effects. Thirdly, nonpharmacological strategies including scheduled sleep times and exercise were accepted and often employed. Lastly, adolescents desired more psychosocial support to address mental health sequelae of narcolepsy that were not fully managed by current treatment modalities.

CONCLUSIONS

Medications were perceived as moderately effective for managing narcolepsy but almost all participants expressed concerns with taking medications due to side effects. Adolescents valued the importance of more holistic care for their narcolepsy treatment such as psychosocial support and nonpharmacological modalities. Further anticipatory guidance regarding pharmacological side effect profiles and better integration with nonpharmacological modalities are needed to improve disease control in adolescent patients.

Hypocretinergic interactions with the serotonergic system regulate REM sleep and cataplexy

Loss of muscle tone triggered by emotions is called cataplexy and is the pathognomonic symptom of narcolepsy, which is caused by hypocretin deficiency. Cataplexy is classically considered to be an abnormal manifestation of REM sleep and is treated by selective serotonin (5HT) reuptake inhibitors. Here we show that deleting the 5HT transporter in hypocretin knockout mice suppressed cataplexy while dramatically increasing REM sleep. Additionally, double knockout mice showed a significant deficit in the buildup of sleep need. Deleting one allele of the 5HT transporter in hypocretin knockout mice strongly increased EEG theta power during REM sleep and theta and gamma powers during wakefulness. Deleting hypocretin receptors in the dorsal raphe neurons of adult mice did not induce cataplexy but consolidated REM sleep. Our results indicate that cataplexy and REM sleep are regulated by different mechanisms and both states and sleep need are regulated by the hypocretinergic input into 5HT neurons.

Narcolepsy is characterized by a sudden loss of muscle tone (cataplexy) similar to REM sleep and is caused by hypocretin deficiency. Here, the authors show that deleting the serotonin transporter gene in hypocretin knockout mice suppresses cataplexy while dramatically increasing REM sleep, indicating that these are two different states but are both regulated by hypocretinergic input to serotonergic neurons.

Therapeutic Strategies for Mitigating Driving Risk in Patients with Narcolepsy

Narcolepsy is a central nervous system hypersomnia disorder characterized by uncontrollable episodes of daytime sleep, sleep state instability, and cataplexy (sudden loss of muscle tone precipitated by emotion). Individuals with narcolepsy report more frequent sleep-related crashes, near crashes, and drowsy driving than drivers with other sleep disorders. As such, evaluating risk of sleep-related crashes is of great importance for this patient population. There are no established guidelines for ensuring driving safety in patients with narcolepsy; however, many providers currently use a combination of subjective report, report of prior crashes or near-misses, report of previously falling asleep while driving, sleepiness screening tools, and maintenance of wakefulness testing (MWT) to determine risk. Driving simulator tests, though often unavailable to the clinician, provide data to support the use of MWT for evaluation of alertness in drivers with narcolepsy. Treatments such as modafinil may improve driving performance; however, the impact of other treatments such as stimulants and sodium oxybate on driving has not been extensively studied. Behavioral and lifestyle modifications may also reduce risk, including scheduled naps, driving only short distances, and avoiding driving after meals, sedating medications, and alcohol intake. Even with effective treatment, alertness in patients with narcolepsy may never reach that of normal drivers; however, studies have suggested that narcolepsy patients may be able to drive safely with appropriate limitations.

Narcolepsy treatment: pharmacological and behavioral strategies in adults and children

Narcolepsy is a disabling, rare, and chronic sleep disorder, currently classified as distinct central nervous system hypersomnia in narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2). Although today a reliable pathogenic hypothesis identifies the cause of NT1 as an autoimmune process destroying hypocretin-producing cells, there is no cure for narcolepsy, and the symptomatic pharmacological available treatments are not entirely effective for all symptoms. Behavioral therapies play a synergistic role in the disease treatment. We here review the available therapeutic options for narcolepsy, including symptomatic pharmacological treatments as well as behavioral and psychosocial interventions that could help clinicians improve the quality of life of patients with narcolepsy in adulthood and childhood.

Clinical and Experimental Human Sleep-Wake Pharmacogenetics

Sleep and wakefulness are highly complex processes that are elegantly orchestrated by fine-tuned neurochemical changes among neuronal and non-neuronal ensembles, nuclei, and networks of the brain. Important neurotransmitters and neuromodulators regulating the circadian and homeostatic facets of sleep-wake physiology include melatonin, γ-aminobutyric acid, hypocretin, histamine, norepinephrine, serotonin, dopamine, and adenosine. Dysregulation of these neurochemical systems may cause sleep-wake disorders, which are commonly classified into insomnia disorder, parasomnias, circadian rhythm sleep-wake disorders, central disorders of hypersomnolence, sleep-related movement disorders, and sleep-related breathing disorders. Sleep-wake disorders can have far-reaching consequences on physical, mental, and social well-being and health and, thus, need be treated with effective and rational therapies. Apart from behavioral (e.g., cognitive behavioral therapy for insomnia), physiological (e.g., chronotherapy with bright light), and mechanical (e.g., continuous positive airway pressure treatment of obstructive sleep apnea) interventions, pharmacological treatments often are the first-line clinical option to improve disturbed sleep and wake states. Nevertheless, not all patients respond to pharmacotherapy in uniform and beneficial fashion, partly due to genetic differences. The improved understanding of the neurochemical mechanisms regulating sleep and wakefulness and the mode of action of sleep-wake therapeutics has provided a conceptual framework, to search for functional genetic variants modifying individual drug response phenotypes. This article will summarize the currently known genetic polymorphisms that modulate drug sensitivity and exposure, to partly determine individual responses to sleep-wake pharmacotherapy. In addition, a pharmacogenetic strategy will be outlined how based upon classical and opto-/chemogenetic strategies in animals, as well as human genetic associations, circuit mechanisms regulating sleep-wake functions in humans can be identified. As such, experimental human sleep-wake pharmacogenetics forms a bridge spanning basic research and clinical medicine and constitutes an essential step for the search and development of novel sleep-wake targets and therapeutics.

[Pharmacotherapy of Sleep-Wake Disorders]

Pharmacotherapy of Sleep-Wake Disorders Abstract. Sleep is a complex behavior, coordinated by many different brain regions and neurotransmitters. These neurochemical systems can be pharmacologically influenced to modulate wakefulness and sleep. Excessive daytime sleepiness (EDS) is often treated with dopaminergic drugs, which in mild cases range from caffeine via (ar)modafinil to amphetamine derivatives. Tricyclic antidepressants and melatonin-based drugs are also used to promote alertness, but to a lesser extent. The drugs used to promote sleep include GABA-ergic drugs such as benzodiazepines and Z-hypnotics as well as histamine H1 receptor antagonists. Exogenous melatonin or a pharmacological combination of melatonin receptor agonists and 5-HT2C receptor antagonists are also used in mild cases. Selective and dual orexin (hypocretin) receptor antagonists (DORA) as well as drugs binding to specific 5-HT receptors are currently being investigated as future sleep-promoting drugs. However, pharmacological treatment is not always the primary treatment option, insomnia is treated first-line with cognitive behavioral therapy, and continuous positive airway pressure is used to treat sleep apnea.

Addressing the Side Effects of Contemporary Antidepressant Drugs: A Comprehensive Review

Randomized trials have shown that selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) have better safety profiles than classical tricyclic antidepressants (TCAs). However, an increasing number of studies, including meta-analyses, naturalistic studies, and longer-term studies suggested that SSRIs and SNRIs are no less safe than TCAs. We focused on comparing the common side effects of TCAs with those of newer generation antidepressants including SSRIs, SNRIs, mirtazapine, and bupropion. The main purpose was to investigate safety profile differences among drug classes rather than the individual antidepressants, so studies containing comparison data on drug groups were prioritized. In terms of safety after overdose, the common belief on newer generation antidepressants having fewer side effects than TCAs appears to be true. TCAs were also associated with higher drop-out rates, lower tolerability, and higher cardiac side-effects. However, evidence regarding side effects including dry mouth, gastrointestinal side effects, hepatotoxicity, seizure, and weight has been inconsistent, some studies demonstrated the superiority of SSRIs and SNRIs over TCAs, while others found the opposite. Some other side effects such as sexual dysfunction, bleeding, and hyponatremia were more prominent with either SSRIs or SNRIs.

Cataplexy and Its Mimics: Clinical Recognition and Management

OPINION STATEMENT

This review describes the diagnosis and management of cataplexy: attacks of bilateral loss of muscle tone, triggered by emotions and with preserved consciousness. Although cataplexy is rare, its recognition is important as in most cases, it leads to a diagnosis of narcolepsy, a disorder that still takes a median of 9 years to be diagnosed. The expression of cataplexy varies widely, from partial episodes affecting only the neck muscles to generalized attacks leading to falls. Moreover, childhood cataplexy differs from the presentation in adults, with a prominent facial involvement, already evident without clear emotional triggers ('cataplectic facies') and 'active' motor phenomena especially of the tongue and perioral muscles. Next to narcolepsy, cataplexy can sometimes be caused by other diseases, such as Niemann-Pick type C, Prader Willi Syndrome, or lesions in the hypothalamic or pontomedullary region. Cataplexy mimics include syncope, epilepsy, hyperekplexia, drop attacks and pseudocataplexy. They can be differentiated from cataplexy using thorough history taking, supplemented with (home)video recordings whenever possible. Childhood narcolepsy, with its profound facial hypotonia, can be confused with neuromuscular disorders, and the active motor phenomenona resemble those found in childhood movement disorders such as Sydenham's chorea. Currently, the diagnosis of cataplexy is made almost solely on clinical grounds, based on history taking and (home) videos. Cataplexy shows remarkable differences in childhood compared to adults, with profound facial hypotonia and complex active motor phenomena. Over time, these severe symptoms evolve to the milder adult phenotype, and this pattern is crucial to recognize when assessing the outcome of uncontrolled case series with potential treatments such as immunomodulation. Symptomatic treatment is possible with antidepressants and sodium oxybate. Importantly, management also needs to involve sleep hygiene advice, safety measures whenever applicable and guidance with regard to the social sequelae of cataplexy.

Formulary Forum: Sodium Oxybate for Cataplexy

Objective:

To review the pharmacology, pharmacokinetics, clinical efficacy, adverse effects, drug interactions, precautions, dosing recommendations, and patient counseling of sodium oxybate for the treatment of cataplexy in patients with narcolepsy.

Data Sources:

OVID and PubMed databases were searched (1966–January 2006) using the key words sodium oxybate, gamma-hydroxybutyrate, narcolepsy, and cataplexy. Only English-language articles were selected.

Study Selection and Data Extraction:

All information on sodium oxybate related to narcolepsy and cataplexy was considered. Study selection included human trials evaluating safety and efficacy of sodium oxybate for the treatment of cataplexy.

Data Synthesis:

Sodium oxybate is approved by the Food and Drug Administration for the treatment of excessive daytime sleepiness and cataplexy in patients with narcolepsy. In placebo-controlled trials, sodium oxybate demonstrated efficacy in reducing the number of cataplexy attacks. The dosing regimen includes a split dose given at bedtime and 2.5–4 hours later due to its short elimination half-life. The drug is generally well tolerated, with headache, nausea, dizziness, pain, and somnolence being the most common adverse events.

Conclusions:

Sodium oxybate is safe and effective for the treatment of cataplexy. Potential disadvantages include a multiple dosing regimen, abuse potential, cost, and a closed distribution system. Potential advantages demonstrated in clinical trials include significant decreases in the number of weekly cataplexy attacks, improvement in daytime sleepiness, and improvement in the Clinical Global Impression of Change score and nighttime awakenings. Overall, sodium oxybate provides a new option for the treatment of cataplexy.

The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality

Narcolepsy is a chronic neurological disease manifesting as difficulty with maintaining continuous wake and sleep. Clinical presentation varies but requires excessive daytime sleepiness (EDS) occurring alone or together with features of rapid-eye movement (REM) sleep dissociation (e.g., cataplexy, hypnagogic/hypnopompic hallucinations, sleep paralysis), and disrupted nighttime sleep. Narcolepsy with cataplexy is associated with reductions of cerebrospinal fluid (CSF) hypocretin due to destruction of hypocretin peptide-producing neurons in the hypothalamus in individuals with a specific genetic predisposition. Updated diagnostic criteria include the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) and International Classification of Sleep Disorders Third Edition (ICSD-3). DSM-5 criteria require EDS in association with any one of the following: (1) cataplexy; (2) CSF hypocretin deficiency; (3) REM sleep latency ≤15 minutes on nocturnal polysomnography (PSG); or (4) mean sleep latency ≤8 minutes on multiple sleep latency testing (MSLT) with ≥2 sleep-onset REM-sleep periods (SOREMPs). ICSD-3 relies more upon objective data in addition to EDS, somewhat complicating the diagnostic criteria: 1) cataplexy and either positive MSLT/PSG findings or CSF hypocretin deficiency; (2) MSLT criteria similar to DSM-5 except that a SOREMP on PSG may count as one of the SOREMPs required on MSLT; and (3) distinct division of narcolepsy into type 1, which requires the presence of cataplexy or documented CSF hypocretin deficiency, and type 2, where cataplexy is absent, and CSF hypocretin levels are either normal or undocumented. We discuss limitations of these criteria such as variability in clinical presentation of cataplexy, particularly when cataplexy may be ambiguous, as well as by age; multiple and/or invasive CSF diagnostic test requirements; and lack of normative diagnostic test data (e.g., MSLT) in certain populations. While ICSD-3 criteria reflect narcolepsy pathophysiology, DSM-5 criteria have greater clinical practicality, suggesting that valid and reliable biomarkers to help standardize narcolepsy diagnosis would be welcomed.

GHB for cataplexy: Possible mode of action

The sleep disorder narcolepsy is caused by the loss of orexinergic neurones in the lateral hypothalamus. A troublesome symptom of narcolepsy is cataplexy, the sudden loss of muscle tone in response to strong emotions. It can be alleviated by antidepressants and sodium oxybate (γ-hydroxybutyric acid (GHB)). It is likely that the noradrenergic nucleus locus coeruleus (LC) is involved since it is essential for the maintenance of muscle tone, and ceases to fire during cataplectic attacks. Furthermore, alpha-2 adrenoceptors proliferate in the LC in cataplexy, probably due to 'heterologous denervation supersensitivity' resulting from the loss/weakening of the orexinergic input to the LC. This would lead to the sensitization of the autoinhibition mechanism of LC neurones mediated by inhibitory alpha-2 adrenoceptors ('autoreceptors'). Thus the excitatory input from the amygdala to the LC, activated by an emotional stimulus, would lead to the 'switching off' of LC activity via the supersensitive auto-inhibition mechanism. GHB is an agonist at both γ-aminobutyric acid (GABA) GABA (B) and GHB receptors that may be a subtype of an extrasynaptic GABA(A) receptor. GHB may prevent a cataplectic attack by dampening the tone of LC neurones via the stimulation of inhibitory extrasynaptic GABA receptors in the LC, and thus increasing the threshold for autoinhibition.

Central Hypersomnia

Sleepiness is not uncommon in the pediatric population. Although the etiology can be multifactorial, sleepiness due to increased sleep drive, also called central hypersomnia, is a common cause. The third edition of the International Classification of Sleep Disorders updated the diagnostic criteria for several of the central disorders of hypersomnolence, most notably narcolepsy. Although the International Classification Of Sleep Disorders-3 is not specific to pediatric patients, the peak incidence for many of the included disorders occurs during childhood or adolescence. As a result, recognition of these lifelong and potentially debilitating disorders is imperative for providers who evaluate pediatric patients. This review provides an update on recent advances in the field and highlights some of the diagnostic dilemmas, unique clinical features, and variable presentations associated with central disorders of hypersomnolence within the pediatric population.

The Neurobiological Mechanisms and Treatments of REM Sleep Disturbances in Depression

Most depressed patients suffer from sleep abnormalities, which are one of the critical symptoms of depression. They are robust risk factors for the initiation and development of depression. Studies about sleep electroencephalograms have shown characteristic changes in depression such as reductions in non-rapid eye movement sleep production, disruptions of sleep continuity and disinhibition of rapid eye movement (REM) sleep. REM sleep alterations include a decrease in REM sleep latency, an increase in REM sleep duration and REM sleep density with respect to depressive episodes. Emotional brain processing dependent on the normal sleep-wake regulation seems to be failed in depression, which also promotes the development of clinical depression. Also, REM sleep alterations have been considered as biomarkers of depression. The disturbances of norepinephrine and serotonin systems may contribute to REM sleep abnormalities in depression. Lastly, this review also discusses the effects of different antidepressants on REM sleep disturbances in depression.

Sodium oxybate for narcolepsy

Sodium oxybate (Xyrem), also known as gamma-hydroxybutyric acid, is the only therapeutic specifically approved in the USA for the treatment of cataplexy in narcolepsy. The US FDA has recently expanded its indication to include excessive daytime sleepiness associated with narcolepsy. In contrast to the antidepressants and stimulants commonly used to treat the disorder, sodium oxybate is the only compound that addresses both sets of symptoms and, when used properly, is less likely to lead to the development of tolerance and other undesirable side effects. In this review, the results of clinical trials and the place of sodium oxybate in narcolepsy treatment are discussed.

Narcolepsy: a review

Narcolepsy is a lifelong sleep disorder characterized by a classic tetrad of excessive daytime sleepiness with irresistible sleep attacks, cataplexy (sudden bilateral loss of muscle tone), hypnagogic hallucination, and sleep paralysis. There are two distinct groups of patients, ie, those having narcolepsy with cataplexy and those having narcolepsy without cataplexy. Narcolepsy affects 0.05% of the population. It has a negative effect on the quality of life of its sufferers and can restrict them from certain careers and activities. There have been advances in the understanding of the pathogenesis of narcolepsy. It is thought that narcolepsy with cataplexy is secondary to loss of hypothalamic hypocretin neurons in those genetically predisposed to the disorder by possession of human leukocyte antigen DQB1*0602. The diagnostic criteria for narcolepsy are based on symptoms, laboratory sleep tests, and serum levels of hypocretin. There is no cure for narcolepsy, and the present mainstay of treatment is pharmacological treatment along with lifestyle changes. Some novel treatments are also being developed and tried. This article critically appraises the evidence for diagnosis and treatment of narcolepsy.

Treatment of narcolepsy

Narcolepsy is a neurological disorder characterized, in its classical form, by excessive daytime sleepiness (EDS) with irresistible episodes of sleep, cataplexy, disrupted nocturnal sleep, hypnagogic/hypnopompic hallucinations and sleep paralysis. It is often under-diagnosed, however, if it is suitably diagnosed, symptoms can be well treated by means of targeted drugs, such as modafinil to treat EDS, sodium oxybate for cataplexy, as well as EDS and disrupted nocturnal sleep, and tricyclic and newer antidepressants for cataplexy. Hallucinations and sleep paralysis can be treated with the same drugs used for cataplexy. Amphetamines and amphetamine-like stimulants are used less nowadays. Behavioral measures are also important and useful. The discovery of hypocretin deficiency in narcoleptic patients opens new perspectives for the development of newer therapeutic approaches for both EDS and cataplexy. Therapy for narcolepsy is chronic, hence symptomatic. However, the correct use of available drugs enables patients to gain a better quality of life, keeping the symptoms under control, which, mainly from a social point of view, are heavily disabling.

Treatment with venlafaxine in six cases of children with narcolepsy and with cataplexy and hypnagogic hallucinations

OBJECTIVE

Narcolepsy with cataplexy is a chronic neuropsychiatric disorder associated with inappropriate control of rapid eye movement (REM) sleep. The main symptoms are excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and disturbed nocturnal sleep. Cataplexy is marked by episodes of muscular weakness and may cause the patient to collapse to the ground. So far, pharmacotherapy of cataplexy and hypnagogic hallucinations has been predominantly based on tricyclic antidepressants. Recently, new drugs that block the reuptake of norepineprine and serotonin (e.g., venlafaxine) have been suggested as first-line treatment. These drugs have become our choice in treating children with cataplexy and nightmares as a symptom in narcolepsy.

METHODS

We describe clinical case reports of venlafaxine treatment in 6 children aged 7-12 years old when diagnosed with narcolepsy-cataplexy.

RESULTS

In 2 cases with up to 50 daily cataplectic attacks, an initial effect of 37.5 mg of venlafaxine was initially observed. However, during the first year, the dose had to be increased to 112.5 mg daily to avoid cataplexy. A third patient with partial cataplexy was treated with 75 mg of venlafaxine daily. In 2 cases, hypnagogic hallucinations, described by the patients as nightmares, were the most troubling symptom and were successfully treated with only 37.5 mg of venlafaxine daily. Side effects included an increase of disturbed nocturnal sleep when venlafaxine was taken after 2:00 p.m. No major aggressive or suicidal thoughts and no raised blood pressure were recorded.

CONCLUSION

Venlafaxine has proven to be an effective treatment of cataplexy and hypnagogic hallucinations in 6 children with narcolepsy. No severe side effects were observed.

Treatment of narcolepsy and other hypersomnias of central origin

OBJECTIVE

The purpose of this paper is to summarize current knowledge about treatment of narcolepsy and other hypersomnias of central origin.

METHODS

The task force performed a systematic and comprehensive review of the relevant literature and graded the evidence using the Oxford grading system. This paper discusses the strengths and limitations of the available evidence regarding treatment of these conditions, and summarizes key information about safety of these medications. Our findings provide the foundation for development of evidence-based practice parameters on this topic by the Standards of Practice Committee of the American Academy of Sleep Medicine.

RESULTS

The majority of recent papers in this field provide information about use of modafinil or sodium oxybate for treatment of sleepiness associated with narcolepsy. Several large randomized, placebo-controlled studies indicate that modafinil and sodium oxybate are effective for treatment of hypersomnia due to narcolepsy. We identified no studies that report direct comparison of these newer medications versus traditional stimulants, or that indicate what proportion of patients treated initially with these medications require transition to traditional stimulants or to combination therapy to achieve adequate alertness. As with the traditional stimulants, modafinil and sodium oxybate provide, at best, only moderate improvement in alertness rather than full restoration of alertness in patients with narcolepsy. Several large randomized placebo-controlled studies demonstrate that sodium oxybate is effective for treatment of cataplexy associated with narcolepsy, and earlier studies provide limited data to support the effectiveness of fluoxetine and tricyclic antidepressants for treatment of cataplexy. Our findings indicate that very few reports provide information regarding treatment of special populations such as children, older adults, and pregnant or breastfeeding women. The available literature provides a modest amount of information about improvement in quality of life in association with treatment, patient preferences among the different medications, or patient compliance.

CONCLUSION

Several recent studies provide evidence that modafinil and sodium oxybate are effective for treatment of hypersomnia due to narcolepsy. No studies were identified that report direct comparison of these newer medications with traditional stimulants. Despite significant advances in understanding the pathophysiology of narcolepsy, we do not have an ideal treatment to restore full and sustained alertness. Future investigations should be directed toward development of more effective and better tolerated therapies, and primary prevention.

Therapies for narcolepsy with or without cataplexy: evidence-based review

(1) Narcolepsy is a rare disorder of unknown aetiology characterized by excessive daytime sleepiness and typically associated with cataplexy. It is extremely incapacitating, and frequently results in impaired psychosocial functioning and reduced work performance. Currently there is no cure for narcolepsy, so treatment focuses on control of symptoms.(2) Although the sympathomimetic stimulants, such as amphetamines or methylphenidate, are effective in improving excessive daytime sleepiness in patients with narcolepsy, they have the potential for dependence, have sometimes disabling sympathomimetic side-effects and are associated with tolerance.(3) To date, there is clear evidence of the efficacy of modafinil, armodafinil and sodium oxybate in patients with narcolepsy. Modafinil and armodafinil improve excessive daytime sleepiness symptoms and have little abuse potential, but have no effect on cataplexy, so other drugs, such as antidepressants, are required to control cataplexy attacks.(4) Sodium oxybate improves both excessive daytime sleepiness and cataplexy. However, there is potential for abuse and possibly dependence.

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.

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.

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.

Molecular genetics and treatment of narcolepsy

Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness and cataplexy. The hypocretin/orexin deficiency is likely to be the key to its pathophysiology in most of cases although the cause of human narcolepsy remains elusive. Acting on a specific genetic background, an autoimmune process targeting hypocretin neurons in response to yet unknown environmental factors is the most probable hypothesis in most cases of human narcolepsy with cataplexy. Although narcolepsy presents one of the tightest associations with a specific human leukocyte antigen (HLA) (DQB1*0602), there is strong evidence that non-HLA genes also confer susceptibility. In addition to a point mutation in the prepro-hypocretin gene discovered in an atypical case, a few polymorphisms in monoaminergic and immune-related genes have been reported associated with narcolepsy. The treatment of narcolepsy has evolved significantly over the last few years. Available treatments include stimulants for hypersomnia with the quite recent widespread use of modafinil, antidepressants for cataplexy, and gamma-hydroxybutyrate for both symptoms. Recent pilot open trials with intravenous immunoglobulins appear an effective treatment of cataplexy if applied at early stages of narcolepsy. Finally, the discovery of hypocretin deficiency might open up new treatment perspectives.

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.