Benefits and risks of pharmacotherapy for narcolepsy

Narcolepsy is a life-long central nervous system (CNS) syndrome characterised by excessive sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations and disturbed night-time sleep. Unsuccessfully treated narcolepsy confers increased risks on patients and on society due to the patient's increased chance of becoming involved in vehicle crashes and workplace mishaps. The syndrome may be diagnosed by a clinical history positive for cataplexy and excessive daytime sleepiness and negative for other more common sleep disorders such as sleep apnoea and sleep deprivation. Night-time polysomnography and multiple sleep latency testing are helpful in differentiating narcolepsy from other sleep problems. Recent data from canine, murine, and human forms of narcolepsy indicate that genetically or developmentally mediated deficits in the hypocretin neurotransmitter system may cause some, but not all, forms of narcolepsy. Pharmacotherapy for narcolepsy is required to control symptoms and involves the use of CNS stimulants or modafinil to control sleepiness and antidepressant medications or sodium oxybate to control cataplexy. Modafinil and sodium oxybate have been developed and approved specifically for the indication of narcolepsy based on large, double-blind, placebo-controlled, parallel group efficacy and safety studies. The efficacy of drugs in the treatment of narcolepsy is variable from patient to patient and usually associated with adverse effects that can limit patient compliance and, therefore, symptom control. Nevertheless, the benefits of pharmacotherapy are judged to outweigh the risks to the patient. The favourable benefit-risk ratio of pharmacotherapy is greater if one considers the reduced risk to society of vehicle crashes and workplace mishaps that might be precipitated by attentional lapses or sleep attacks in the untreated or under-treated patient with narcolepsy.

Sexual dimorphism of the catechol-O-methyltransferase gene in narcolepsy is associated with response to modafinil

The gene for catechol-O-methyltransferase (COMT) plays a key modulatory role in dopaminergic and noradrenergic neurotransmission. Recent evidence suggests that modafinil, like other stimulants, might act through the dopaminergic system. We have reported a sexual dimorphism and a strong effect of the COMT genotype on narcolepsy symptoms and hypothesized that response to modafinil treatment may be associated with the COMT genotype. Here we confirm that COMT genotype distribution between men and women narcoleptics is associated with response to modafinil. In addition, the optimal daily dose of modafinil is approximately 100 mg lower in women narcoleptics and lower in all narcoleptics with low activity COMT genotype. Our results suggest that a sexual dimorphism in COMT activity affects the response to modafinil and probably to other dopaminergic stimulants.

Secondary narcolepsy in children with brain tumors

We report two cases of children with disabling daytime sleepiness associated with suprasellar tumors and hypothalamic obesity. Multiple sleep latency testing demonstrated features consistent with severe narcolepsy, with sleep latencies of 0.25 and 0.75 minutes, and REM latencies of 2.1 and 1.5 minutes, respectively. An additional patient with hypothalamic damage secondary to a brain tumor, who was thought to be in a vegetative state, had features of narcolepsy on polysomnography. All children responded well to treatment with stimulants. We speculate that secondary narcolepsy associated with hypothalamic tumors is due to damage or loss of hypothalamic hypocretin-containing neurons. In view of the good response to treatment, we recommend that all children with excessive daytime sleepiness and hypothalamic damage be evaluated for narcolepsy.

Awakening to the psychopharmacology of sleep and arousal: novel neurotransmitters and wake-promoting drugs

Exciting new developments in the psychopharmacology of wakefulness are clarifying the neurotransmitters, pathways, and drugs that impact this important physiologic state. Selectively inducing normal wakefulness without stimulating external vigilance may lead to therapeutic benefits not only in sleep disorders but also in cognitive disorders and conditions associated with fatigue.

The neurobiology of narcolepsy-cataplexy syndrome

The pathophysiology of narcolepsy is closely related to the abnormalities of REM sleep that are the electrophysiologic signature of the syndrome. Evidence from studies of canine narcolepsy and postmortem human narcoleptic brain tissue provide strong evidence that cholinergic and monoaminergic systems involved in REM sleep regulation are abnormal in narcolepsy but the primary neurochemical abnormality has not yet been determined. There is now conclusive evidence that a genetic basis is required for all or almost all cases of narcolepsy. In the vast majority of narcoleptics, a gene closely linked to the HLA-DR/DQ region appears to confer narcoleptic susceptibility, but the penetrance of the gene is low and additional environmental and perhaps genetic factors are required to express the disease. In a minority of narcoleptics, there may be a second autosomal dominant gene not linked to HLA-DR2 that facilitates the occurrence of narcolepsy. This gene may be related to the mu-immunoglobulin heavy-chain switch-like segment that has been implicated in canine narcolepsy. There appear to be at least two narcoleptic phenotypes associated with the narcoleptic susceptibility gene or genes: narcolepsy-cataplexy syndrome and monosymptomatic narcolepsy, or narcolepsy with REM sleep abnormalities but without cataplexy. Idiopathic hypersomnia without cataplexy or REM sleep abnormalities may represent a third phenotype, although most cases of idiopathic hypersomnia are probably unrelated to the HLA-D linked gene. The link between the genetic basis of narcolepsy and its neurochemical abnormalities is still entirely unknown. Although the hypothesis that a transient immune-mediated reaction leads to a permanent alteration of monoaminergic function is appealling, there is no direct evidence to support this hypothesis. Several important questions concerning the neurobiology of narcolepsy remain to be answered. What is the specific gene in the HLA-D region that is linked to human narcolepsy and what are the products or functions of the gene that predispose to narcolepsy? Does the human mu-switch region contain genetic material homologous to the 85-kb band linked to canarc-1 that predisposes to narcolepsy? What are the environmental factors required for expression of the disease in susceptible individuals and do they incite immunologic processes? Which of the neurochemical abnormalities are primary, which are secondary or compensatory, and how do they relate to the predisposing genetic and environmental elements? Additional familial, genetic, and neurochemical studies over the next decade should lead to more complete understanding of the neurobiology of narcolepsy and ultimately to better treatments for this chronic disabling disease.

Hypersomnolence and narcolepsy; a pragmatic diagnostic neurophysiological approach

Out of a group of 250 consecutive patients who were examined for various disorders of sleep and waking at Ghent University Hospital within a period of 24 months, 30 patients with hypersomnolence associated with a suspected underlying neurological etiology were selected. The population consisted of 15 males and 15 females with mean age of 36 years (range: 16-60 years). Twenty-one patients had had hypersomnolence for more than 2 years. All patients underwent a single night polysomnography (PSG) and a 4-nap multiple sleep latency test (MSLT). PSG was normal in 23 patients. Sleep onset REM period (SOREMP) was defined as the occurrence of REM sleep within 15 min. after initiation of sleep. PSG demonstrated SOREMP's in only 1 patient and showed evidence of obstructive sleep apnea in 4 patients. Two patients had a low sleep efficiency. MSLT demonstrated hypersomnolence in 17 patients of whom 6 showed SOREMP. Significant hypersomnolence was defined as a mean sleep latency < or = 5 min. 4 patients fulfilled the classical clinical and polygraphic criteria (> or = 2 SOREMP) of narcolepsy. In 8 patients the tentative diagnosis of idiopathic CNS hypersomnolence was made. 13 patients did not sleep during MSLT. These results emphasize the relative importance of MSLT. Our limited 4-nap MSLT protocol proved useful in distinguishing narcolepsy from idiopathic CNS hypersomnolence.

Practice parameter for the use of stimulant medications in the treatment of children, adolescents, and adults

This practice parameter describes treatment with stimulant medication. It uses an evidence-based medicine approach derived from a detailed literature review and expert consultation. Stimulant medications in clinical use include methylphenidate, dextroamphetamine, mixed-salts amphetamine, and pemoline. It carries FDA indications for treatment of attention-deficit/hyperactivity disorder and narcolepsy.

A randomized, double blind, placebo-controlled multicenter trial comparing the effects of three doses of orally administered sodium oxybate with placebo for the treatment of narcolepsy

STUDY OBJECTIVES

To evaluate and compare the efficacy and safety of three doses of sodium oxybate and placebo for the treatment of narcolepsy symptoms.

DESIGN

A multicenter, double blind, placebo-controlled trial.

SETTING

N/A.

PARTICIPANTS

Study subjects were 136 narcolepsy patients with 3 to 249 (median 21) cataplexy attacks weekly.

INTERVENTIONS

Prior to baseline measures, subjects discontinued anticataplectic medications. Stable doses of stimulants were permitted. Subjects were randomized in blinded fashion to receive 3, 6, or 9 g doses of sodium oxybate or placebo taken in equally divided doses upon retiring to bed and 2.5-4 hours later for 4 weeks.

MEASUREMENTS AND RESULTS

Disease symptoms and adverse events were recorded in daily diaries. The primary measure of efficacy was the change from baseline in weekly cataplexy attacks. Secondary measures included daytime sleepiness using the Epworth Sleepiness Scale (ESS), inadvertent daytime naps/sleep attacks and nighttime awakenings. Investigators assessed changes in disease severity using Clinical Global Impression of Change (CGI-c). Compared to placebo, weekly cataplexy attacks were decreased by sodium oxybate at the 6 g dose (p=0.0529) and significantly at the 9 g dose (p=0.0008). The ESS was reduced at all doses, becoming significant at the 9 g dose (p=0.0001). The CGI-c demonstrated a dose-related improvement, significant at the 9 g dose (p=0.0002). The frequency of inadvertent naps/sleep attacks and the nighttime awakenings showed similar dose-response trends, becoming significant at the 9 g dose (p=0.0122 and p=0.0035, respectively). Sodium oxybate was generally well-tolerated at all three doses. Nausea, headache, dizziness and enuresis were the most commonly reported adverse events.

CONCLUSIONS

Sodium oxybate significantly improved symptoms in patients with narcolepsy and was well tolerated.

Gamma-Hydroxybutyrate (orphan medical)

Orphan Medical is developing gamma-hydroxybutyrate (Xyrem) for the potential treatment of narcolepsy [183352]. In October 2000, an NDA was filed with the FDA [384422], [405504] and Xyrem received an FDA approvable letter in July 2001. Orphan Medical stated that it believed it could meet the requirements in the letter, including a trial in respiratory-compromised patients, by the end of 2001 [414461]. The FDA also requested follow-up safety data from patients in previous Xyrem trials. At that time, the drug was not expected to be launched until mid-2002 [415301], [416305]. In October 1999, the US House of Representatives passed the HR 2130 bill, allowing the medical use of gamma-hydroxybutyrate, which is classified as a Schedule I controlled substance in the US [343562]; the Senate approved this legislation in November 1999 [348206]. In February 2000, a congressional bill supporting the continued development of medically formulated gamma-hydroxybutyrate was passed, making medically formulated gamma-hydroxybutyrate products Schedule III substances [354108], [356597]. GHB occurs naturally in many human tissues. It has previously been used in the treatment of narcolepsy and is not patentable for that indication.

[Hypocretin (orexin) deficiency in narcolepsy-cataplexy]

A mutation in the HCRT locus was proved in 18-yrs old male suffering from narcolepsy-cataplexy. He has demonstrated cataplectic attacks (brief spells of head dropping provoked by laughter) as well as imperative sleep in spells of several minutes up to one hour since the age of six months. He has suffered from severe bulimia since five years; later hypnagogic hallucinations, sleep paralysis and unquiet nocturnal sleep accompanied by periodic limb movements appeared. Symptoms are partially controlled with methylphenidate and either imipramine, clomipramine or fluoxetine. Periodic leg movements poorly responded to L-DOPA and clonazepam treatment. He is HLA-DQB1*0602 negative. Repeated MSLT (over 16 years followed-up period) showed extremely short latency with predominant SOREMPs and also nocturnal PSG recordings revealed fragmented sleep with SOREMPs. This case report demonstrates that hypocretin (orexin) mutations in human can produce the full narcolepsy phenotype and validates data recently reported in dog and mouse models suggesting a role for hypocretin (orexin) in the pathophysiology of narcolepsy and the regulation of REM sleep.

Systemic administration of hypocretin-1 reduces cataplexy and normalizes sleep and waking durations in narcoleptic dogs

Recent work has implicated the hypocretin (orexin) system in the genesis of narcolepsy. In the current study we demonstrate that systemically administered hypocretin-1 (Hcrt-1) produces an increase in activity level, longer waking periods, a decrease in REM sleep without change in nonREM sleep, reduced sleep fragmentation and a dose dependent reduction in cataplexy in canine narcoleptics. Repeated administration of single daily doses of Hcrt-1 led to consolidation of waking and sleep periods and to a complete loss of cataplexy for periods of three or more days after treatment in animals that were never asymptomatic under control conditions. Systemic administration of Hcrt-1 may be an effective treatment for narcolepsy.

[Unwanted napping]

Three patients, one woman aged 43, and two men aged 32 and 51, suffered from excessive daytime sleepiness with different causes. The woman experienced nocturnal motor attacks of epileptic origin, responding to carbamazepine. The diagnosis was based on polysomnographic recordings combined with video monitoring. Narcolepsy was diagnosed in the 32-year-old man. He also suffered from cataplexy. The diagnosis was supported by a multiple sleep latency test and HLA-DR2 positivity. He was treated with clomipramine. In the 43-year-old man an obstructive sleep apnoea syndrome was diagnosed by polysomnographic recording. He was treated successfully with continuous positive airway pressure. These patients show that excessive daytime sleepiness is sometimes difficult to recognise and can be a potentially incapacitating symptom of a treatable underlying disorder. Diagnosis is made by careful history taking and through the use of different types of somnographic recordings.

[Narcolepsy in children]

INTRODUCTION

Narcolepsy is a neurological disorder characterized by excessive somnolence during the daytime, with recurrent, irresistible episodes of sleepiness. The complete forms are associated with cataplexy, hypnagogic hallucinations and sleep paralysis. The incidence reported in adults is 4 10/10,000. A considerable proportion of adults consider their disorder to have started before the age of 15 years. It is essential to have neurophysiological confirmation of the short period of the onset of REM sleep for diagnosis.

CLINICAL CASE

An 11 year old boy with diurnal hypersomnolence, behavior disorder and weight gain. He was evaluated in the Sleep Disorder Unit by polysomnography and the multiple latency test, which confirmed the suspicion of narcolepsy.

CONCLUSIONS

Narcolepsy is a disorder which starts during childhood and usually goes unnoticed or is erroneously diagnosed and treated. At the present time there are valid criteria for the identification and diagnosis of children with this disorder. Treatment of these patients should be orientated towards adaptation of the environment to the child and prevention of the psychosocial problems which may be caused by this disorder, in view of the poor response to the drugs used.

New insights into the pathogenesis and treatment of narcolepsy

Narcolepsy is a complex neurologic disorder, which has significant negative impacts on the lives of those who have it. Although the disorder is treatable, traditional methods do not alleviate symptoms completely and often produce unwanted side effects. Fortunately, recent advances in the understanding of narcolepsy offer the promise of improved treatments in the foreseeable future.

[Narcolepsy in a prepubertal boy]

We reported a 10-year-old boy with narcolepsy, the onset of which was at the age of 8 years and 6 months. The initial symptom was excessive daytime sleepiness, followed by cataplexy and disrupted nocturnal sleep. There was neither hallucination nor sleep paralysis. A daytime polysomnogram showed a sleep-onset rapid eye movement period (SOREMP), and human leukocyte antigen (HLA) analysis revealed HLA-DR2/DQB1 * 0602. Treatment with methylphenidate and clomipramine was effective; methylphenidate (30 mg/day) improved his wakefulness and alertness throughout the day, and clomipramine (20 mg/day) reduced the number of cataplexic episodes. Because of their abnormal behavior, prepubertal narcoleptic children may often be misdiagnosed as having epilepsy or an attention deficit hyperactivity disorder. Therefore, they need early diagnosis and treatment. Assistance should be provided to protect them from being labeled as lazy by their parents and school teachers.

A commentary on the neurobiology of the hypocretin/orexin system

Hypocretins/orexins are rapidly emerging as functionally important neurotransmitters. Two related neuropeptides (Hcrt-1/OXA, Hcrt-2/OXB) encoded by the same precursor gene and two G-protein coupled receptors (Hcrtr1/OXR1, Hcrtr2/OXR2) are currently known. Hypocretin-containing cells are discretely localized within the perifornical hypothalamus but have widespread projections, with generally excitatory postsynaptic effects. Dense excitatory projections to all monoaminergic cell groups have been reported. A major emerging function for this system is likely to be the regulation of sleep. Alterations in hypocretin neurotransmission causes the sleep disorder narcolepsy in mice, dogs and humans. Effects on appetite, neuroendocrine and energy metabolism regulation are also suggested by other studies. Hypocretins are uniquely positioned to link sleep, appetite and neuroendocrine control, three behaviors of major importance in psychiatry. The potential role of this system in regulating the sleep cycle, modulating wakefulness at selected circadian times and in mediating the deleterious effects of sleep deprivation is discussed.

Increased dopaminergic transmission mediates the wake-promoting effects of CNS stimulants

Amphetamine-like stimulants are commonly used to treat sleepiness in narcolepsy. These compounds have little effect on rapid eye movement (REM) sleep-related symptoms such as cataplexy, and antidepressants (monoamine uptake inhibitors) are usually required to treat these symptoms. Although amphetamine-like stimulants and antidepressants enhance monoaminergic transmission, these compounds are non-selective for each monoamine, and the exact mechanisms mediating how these compounds induce wakefulness and modulate REM sleep are not known. In order to evaluate the relative importance of dopaminergic and noradrenergic transmission in the mediation of these effects, five dopamine (DA) uptake inhibitors (mazindol, GBR-12909, bupropion, nomifensine and amineptine), two norepinephrine (NE) uptake inhibitors (nisoxetine and desipramine), d-amphetamine, and modafinil, a non-amphetamine stimulant, were tested in control and narcoleptic canines. All stimulants and dopaminergic uptake inhibitors were found to dose-dependently increase wakefulness in control and narcoleptic animals. The in vivo potencies of DA uptake inhibitors and modafinil on wake significantly correlated with their in vitro affinities to the DA and not the NE transporter. DA uptake inhibitors also moderately reduced REM sleep, but this effect was most likely secondary to slow wave sleep (SWS) suppression, since selective DA uptake inhibitors reduced both REM sleep and SWS proportionally. In contrast, selective NE uptake inhibitors had little effect on wakefulness, but potently reduced REM sleep. These results suggest that presynaptic activation of DA transmission is critical for the pharmacological control of wakefulness, while that of the NE system is critical for REM sleep regulation. Our results also suggest that presynaptic activation of DA transmission is a key pharmacological property mediating the wake-promoting effects of currently available CNS stimulants.