Preliminary clinical trial with L-DOPA in Narcolepsy

Narcolepsy in the older adult: epidemiology, diagnosis and management

Narcolepsy is a disorder of impaired expression of wakefulness and rapid-eye-movement (REM) sleep. This manifests as excessive daytime sleepiness and expression of individual physiological correlates of REM sleep that include cataplexy and sleep paralysis (REM sleep atonia intruding into wakefulness), impaired maintenance of REM sleep atonia (e.g. REM sleep behaviour disorder [RBD]), and dream imagery intruding into wakefulness (e.g. hypnagogic and hypnopompic hallucinations). Excessive sleepiness typically begins in the second or third decade followed by expression of auxiliary symptoms. Only cataplexy exhibits a high specificity for diagnosis of narcolepsy. While the natural history is poorly defined, narcolepsy appears to be lifelong but not progressive. Mild disease severity, misdiagnoses or long delays in cataplexy expression often cause long intervals between symptom onset, presentation and diagnosis. Only 15-30% of narcoleptic individuals are ever diagnosed or treated, and nearly half first present for diagnosis after the age of 40 years. Attention to periodic leg movements (PLM), sleep apnoea and RBD is particularly important in the management of the older narcoleptic patient, in whom these conditions are more likely to occur. Diagnosis requires nocturnal polysomnography (NPSG) followed by multiple sleep latency testing (MSLT). The NPSG of a narcoleptic patient may be totally normal, or demonstrate the patient has a short nocturnal REM sleep latency, exhibits unexplained arousals or PLM. The MSLT diagnostic criteria for narcolepsy include short sleep latencies (<8 minutes) and at least two naps with sleep-onset REM sleep. Treatment includes counselling as to the chronic nature of narcolepsy, the potential for developing further symptoms reflective of REM sleep dyscontrol, and the hazards associated with driving and operating machinery. Elderly narcoleptic patients, despite age-related decrements in sleep quality, are generally less sleepy and less likely to evidence REM sleep dyscontrol. Nonpharmacological management also includes maintenance of a strict wake-sleep schedule, good sleep hygiene, the benefits of afternoon naps and a programme of regular exercise. Thereafter, treatment is highly individualised, depending on the severity of daytime sleepiness, cataplexy and sleep disruption. Wake-promoting agents include the traditional psychostimulants. More recently, treatment with the 'activating' antidepressants and the novel wake-promoting agent modafinil has been advocated. Cataplexy is especially responsive to antidepressants which enhance synaptic levels of noradrenaline (norepinephrine) and/or serotonin. Obstructive sleep apnoea and PLMs are more common in narcolepsy and should be suspected when previously well controlled older narcolepsy patients exhibit a worsening of symptoms. The discovery that narcolepsy/cataplexy results from the absence of neuroexcitatory properties of the hypothalamic hypocretin-peptidergic system will significantly advance understanding and treatment of the symptom complex in the future.

Pharmacological aspects of human and canine narcolepsy

Narcolepsy-cataplexy is a disabling neurological disorder that affects 1/2000 individuals. The main clinical features of narcolepsy, excessive daytime sleepiness and symptoms of abnormal REM sleep (cataplexy, sleep paralysis, hypnagogic hallucinations) are currently treated using amphetamine-like compounds or modafinil and antidepressants. Pharmacological research in the area is facilitated greatly by the existence of a canine model of the disorder. The mode of action of these compounds involves presynaptic activation of adrenergic transmission for the anticataplectic effects of antidepressant compounds and presynaptic activation of dopaminergic transmission for the EEG arousal effects of amphetamine-like stimulants. The mode of action of modafmil is still uncertain, and other neurochemical systems may offer interesting avenues for therapeutic development. Pharmacological and physiological studies using the canine model have identified primary neurochemical and neuroanatomical systems that underlie the expression of abnormal REM sleep and excessive sleepiness in narcolepsy. These involve mostly the pontine and basal forebrain cholinergic, the pontine adrenergic and the mesolimbic and mesocortical dopaminergic systems. These studies confirm a continuing need for basic research in both human and canine narcolepsy, and new treatments that act directly at the level of the primary defect in narcolepsy might be forthcoming.

Compound narcolepsy: development of biochemical imbalance

In a review of existing literature, compound narcolepsy is shown to involve not only problems of sleep regulation, but also autonomic, hormonal, emotional, and possibly motor and cognitive dysfunctions, strongly implicating the hypothalamus, limbic system, and possibly the striatum and cortex in the disorder. Neurochemical studies and the pattern of narcoleptic symptoms support the idea of a dynamic imbalance between dopamine and acetylcholine in the etiology of the disorder. What is known about the natural history of compound narcolepsy suggests a developmental course beginning with fluctuations in dopamine release, followed by supersensitivity of dopamine autoreceptors, and later followed by a pattern of intrinsic oscillations and reciprocal "overshoots" in release of dopamine and acetylcholine to account for the typical sequence of appearance of narcoleptic symptoms.

The neurobiology of the narcoleptic syndrome

Relevant electroencephalographic, psychopharmacologic, and genetic research reports are described in support of a neurobiological explanation of the narcoleptic syndrome. Despite increased support in this realm, no single neurobiological theory has won unanimous approval among sleep researchers, which has led toward speculation that the condition may be heterogeneous in nature. A multifactorial perspective, including psychological as well as neurobiological influences, appears to be the most productive model for research. Future investigation of sleep disorders utilizing such a model may enhance the understanding of neurobiological correlates of behavioural disorders.

Genetic markers in narcolepsy

Narcolepsy has long been known to have a hereditary familial basis. All of 37 patients with narcolepsy expressed the major histocompatibility complex antigen HLA DR2 compared with 21.5% of 200 normal controls. This finding confirms the genetic basis for the disease, and furthermore links it with the short arm of chromosome 6. If the sleep disturbance in narcolepsy is due to a gene-determined defect in a neurotransmitter or receptor factor, the responsible agent may be DR2 itself or an enzyme determinant linked to DR2. This is the strongest HLA-disease association so far discovered.

Kleine-Levin syndrome with periodic apnea during hypersomnic stages--E.E.G. study

A 33 year old male, suffering from Kleine-Levine syndrome associated with periods of apnea during the hypersomnic attacks, is reported. Ventilatory studies negate the Pickwickian syndrome. The E.E.G.'s recorded during the hypersomnic attacks and the apneic periods showed a direct correlation between high-voltage delta waves paroxysmal E.E.G. activity, and apneic period. Medications known to improve Kleine-Levin syndrome, in our case, had no effect upon the clinical hypersomnic and apnea periods, nor on the correlatives E.E.G.'s pattern and spirometric studies. Theoretical considerations let us assume that these paroxysmal E.E.G. patterns associated with apnea are NRem-sleep serotonin dependent, and have an inhibitory influence on the respiratory centers, by alternating the equilibrium between the catecholamines and acetylcholine activities.