Rapid eye movements, muscle twitches and sawtooth waves in the sleep of narcoleptic patients and controls

Seventeen unmedicated patients with narcolepsy-cataplexy and 17 age- and sex-matched controls were recorded polygraphically for 3 consecutive nights. Rapid eye movements (REMs), m. mentalis twitches and sawtooth waves in the EEG were visually scored. REM and twitch densities during REM sleep were significantly higher in the patients than in the controls. The distribution pattern of REMs and twitches was altered in the patients: twitch density peaked in the first REM period and density of REMs showed an even distribution across all the REM periods of the night. In the controls both REM and twitch density increased from the first to the second REM period. We therefore assume that in the narcoleptics phasic activity of REM sleep is disinhibited. Densities of REMs, twitches and sawtooth waves did not correlate with one another in patients and controls. They appear to be independently regulated. The REM periods of the patients contained 3 times as many waking epochs as those of the controls. This suggests that in narcolepsy the transition REM/waking is selectively facilitated. The REM/NREM ratio of twitch and sawtooth wave densities was the same in patients and controls.

Complex event-related potentials (P300 and CNV) and MSLT in the assessment of excessive daytime sleepiness in narcolepsy-cataplexy

The P300 and contingent negative variation (CNV) evoked potential (EP) paradigms were performed by 12 untreated narcoleptics and controls immediately prior to each nap of the Multiple Sleep Latency Test (MSLT) in order to assess whether they might hold promise as rapid quantitative techniques to assess excessive daytime sleepiness. The Stanford Sleepiness Scale (SSS) was also completed across test days and immediately before and after both the evoked potential recordings and MSLT naps. MSLT findings confirmed shorter sleep latencies and frequent SOREMPs in narcoleptics and a strong mid-afternoon increase in sleepiness based upon pressure for NREM sleep in both groups. On SSS narcoleptics were sleepier and they showed greater increase in sleepiness induced by the EP tests and greater sleepiness reduction by the MSLT naps. In the P300 paradigm, narcoleptics showed smaller component P3 amplitudes and larger P1 amplitudes. In the CNV paradigm, N1 latencies were greater in narcoleptics to both S1 and S2 and the post-CNV negative component was larger: but no significant differences were seen for the main CNV measures of negativity amplitude in the first or second halves of the response. The P300 paradigm but not the CNV, therefore, appeared to be a sensitive EP measure of sleepiness. Finally, EP components in both the P300 and CNV paradigms showed time-of-day (circadian) differences between narcoleptics and controls.

Differences between REM and NREM sleepiness measured by event-related potentials (P300, CNV), MSLT and subjective estimate in narcolepsy-cataplexy

Differences between 'REM sleepiness' and 'NREM sleepiness' states in wakefulness studied respectively prior to REM-containing and NREM-only multiple sleep latency test (MSLT) naps were compared by complex evoked potentials (P300, CNV), subjective estimate (Stanford Sleepiness Scale, SSS) and MSLT measures in 12 untreated patients with narcolepsy-cataplexy. The EP paradigms lasted about 7 min each and were done during the 10 min immediately before MSLT naps at 10.00, 12.00, 14.00, 16.00 and 18.00 h. SSS forms were completed immediately before and after the EP studies and MSLT naps. Patients were studied on 2 days and performed either the P300 or CNV paradigm on each day. 'REM sleepiness' was found to be subjectively and objectively (shorter mean sleep latency on MSLT) greater. Although subjects were sleepier in REM sleepiness, the subsequent REM nap was relatively more refreshing and reduced SSS estimates to levels equivalent to those after NREM-only naps. EP measures also showed differences between the 2 sleepiness states. REM sleepiness was associated with a significantly larger P2 component (in both the P300 paradigm and the CNV paradigm), a strong but not significant trend towards reduced amplitude of the P3 component, and almost total suppression of the slow negative components of the CNV. REM sleepiness and NREM sleepiness therefore appear to be district and differentiable cerebral states.

Narcolepsy/cataplexy. IV: Diagnostic value of daytime nap recordings

Sleep and wakefulness patterns in daytime naps of 50 patients with narcolepsy/cataplexy were compared with those of 50 controls. Each subject was monitored polygraphically during 2 one-hour nap periods. A sleep-onset REM period in either of the 2 daytime naps was observed to have a higher diagnostic sensitivity (78%) than an abnormally shortened sleep latency (68%). However, the specificities of a sleep-onset REM period (88%) or abnormally shortened sleep latency (90%) were quite similar. When the occurrence of either a sleep-onset REM period or a shortened sleep latency was evaluated in either of the two naps, the overall sensitivity was increased to 84% while the specificity was decreased only to 80%. The limitations of and indications for the use of testing for sleep and REM latencies in the diagnosis of narcolepsy in clinical practice are discussed.

Narcolepsy/cataplexy. III: Nocturnal sleep and wakefulness patterns

Nocturnal sleep and wakefulness patterns of 50 patients with narcolepsy and cataplexy were compared to those of 50 control subjects. A sleep onset REM period (SOREM) occurred in 22 (44%) of the patients but in none of the controls. Comparisons among patients showing a SOREM, patients without this abnormality, and controls demonstrated that the timing, number and duration of the remaining REM periods did not differ across the three groups. Thus, the basic REM sleep disturbance in narcolepsy appears to relate to the timing of onset of the initial REM period. This finding lends further support to the theory of dual control of REM-NREM cycling. While narcoleptics took significantly less time to fall asleep, they had significantly more awakenings, wake time after sleep onset and total wake time. The disturbed sleep experienced by patients could not be accounted for by the presence of a sleep onset REM period or the use of medication. Nocturnal wakefulness appeared to be distributed in a regular oscillating manner throughout the recording period similar to the pattern of daytime vigilance previously reported in normal subjects. Thus, typical nocturnal dampening of daytime ultradian vigilance rhythms may be lost in the narcoleptic patient.

The management of drop attacks

From the preceding it is evident that drop attacks can result from a myriad of causes. As in all situations, the patient's history and the clinical picture are the most important factors in arriving at the appropriate diagnosis. However, understanding the neurophysiologic basis of posture should prove significantly helpful in this endeavor.

Sleep fragmentation in canine narcolepsy

Genetically narcoleptic dogs were recorded continuously for 24 h to examine their sleep-wake patterns and to evaluate the extent of sleep fragmentation. Three narcoleptic and three control dogs from each of two affected breeds (Labrador retrievers and Doberman pinschers) were surgically implanted with electrodes for recording standard sleep parameters. Recordings were scored in 30-s epochs for the states of active waking, drowsiness, light sleep, deep slow wave sleep, REM sleep, and cataplexy. All affected dogs displayed marked fragmentation and disruption of the sleep-wake cycle characterized by repeated awakenings, frequent shifts in sleep stages, numerous attacks of cataplexy occurring from active waking, and a disturbance of the normal REM-NREM periodicity. This sleep disruption was reflected in significantly greater numbers of episodes of each behavioral state as well as in a 38% increase in the total number of all states. These results demonstrate a severe disturbance of the normal sleep pattern in canine narcoleptics. The possibility of a general dysfunction of circadian organization is discussed.

Narcolepsy, cataplexy, heart rate, and blood pressure

Seven narcoleptic patients had serial measurements of blood pressure taken during nocturnal sleep over a period of 2 or 3 successive nights. Blood pressure was measured using a Doppler system with a cuff that automatically inflates every 15 min. There was no difference in the blood pressure measurements throughout the night compared with normal control subjects. Blood pressure followed the patterns of normal nocturnal variation; there was a nonsignificant increase in REM sleep compared with stage 3-4 NREM sleep. Studies of heart rate immediately preceding cataplectic attacks were inconclusive in identifying cardiovascular changes preceding muscle weakness.

Serotoninergic reuptake mechanisms in the control of cataplexy

Zimelidine, a selective inhibitor of serotonin (5-HT) reuptake in the CNS, was administered to narcoleptic patients. This medication has a potent anticataplectic action without improving daytime somnolence. These results suggest that 5-HT neuronal systems are involved in the physiopathology of cataplexy. Zimelidine, however, has no anticholinergic effect, so it is unlikely that cholinergic mechanisms thought to be important in animal cataplexy would play a major role in human cataplexy. In addition, zimelidine had no effect on nocturnal sleep patterns of these patients which is surprising considering the importance of 5-HT neuronal systems in sleep physiology. A 5-HT hypothesis of cataplexy is formulated, and the mechanisms of action of other anticataplectic agents are discussed.

Erectile dysfunction in narcoleptic patients

Many male narcoleptic patients complain of erectile dysfunction related to chemotherapy, and some find it so distressing that they fail to continue treatments. This is a potentially dangerous situation. We studied the erectile capabilities of 28 narcoleptic men who had complaints of erectile dysfunction with our objective sleep laboratory measurement of nocturnal penile tumescence (NPT) for diagnostic workup. We found that while short REM latency, a classic indicator of narcolepsy, was present in all patients, NPT, which is associated with REM sleep, did not coincide with the short REM latencies in about half the patients. This may be partially due to the fact that first-cycle REM is often not accompanied by NPT episodes (even in the control population). We also found that, in a few cases, the patients' subjective beliefs about their erectile capacity tended to underestimate our measurements. The patients receiving drug treatment already had some vasculogenic or neurogenic genital impairment, which probably made them more vulnerable to the effects of the drugs. Patients who had none of these complications showed similar erectile impairment under the influence of medication. Additionally, we found unique manifestations of the disease in three drug-free patients; one had cataplectic attacks upon arousal, and two had unexplained erectile impairment.

Excessive daytime sleepiness and the pathophysiology of narcolepsy-cataplexy: a laboratory perspective

The main disabling symptom of narcolepsy-cataplexy is shown to be the unrelenting excessive daytime sleepiness (EDS) based upon controlled studies of socioeconomic effects and the poor response to treatment. Objective performance deficits mainly involve tests of ability to sustain performance on repetitive boring tasks and are reversible by improved alertness. Physiologically, EDS is seen to represent relatively slow waxing and waning of alertness rather than punctate microsleeps. Evidence is provided for complex cerebral evoked potentials (P300, contingent negative variation) being very sensitive EDS measures comparable to the multiple sleep latency test (MSLT). EDS appears to have qualitatively somewhat different forms mainly reflecting pressure for REM sleep (REM sleepiness) or pressure for NREM sleep (NREM sleepiness), which have different effects on cerebral evoked potentials as well as subjective and objective (MSLT) differences. It is argued that in pathophysiological terms narcolepsy may best be considered a disease of state boundary control.

Heart rate and blood pressure changes associated with cataplexy in canine narcolepsy

Blood pressure and heart rate were monitored in narcoleptic dogs by means of a chronically implanted catheter placed in the descending aorta. Changes in these variables were recorded during spontaneously occurring cataplectic episodes. We found no reliable change in blood pressure associated with cataplexy onset. However, heart rate showed a marked increase prior to the onset of cataplexy, with peak heart rates being reached at or shortly after the disappearance of muscle tone. Autonomic events correlated with increased heart rate may contribute to the triggering of cataplexy in narcoleptics.

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.

Cataplexy brought on by playing checkers

A 55-year-old man had experienced spells of weakness and trembling daily for 24 years before the correct diagnosis of cataplexy was reached. While the patient played checkers, the degree of cataplexy worsened when it was the patient's move and improved when it was his opponent's. Response to therapy was excellent.

Auditory evoked potentials compared to performance measures and EEG in assessing excessive daytime sleepiness in narcolepsy-cataplexy

The AEP to the repetitive stimuli of the Wilkinson auditory vigilance task was compared between untreated patients with narcolepsy-cataplexy and matched controls for periods during which the tones were preceded by 13 sec or more of wakefulness (defined by EEG-polygraphic criteria). During these periods it had been found previously that narcoleptics did not perform worse than did controls. The AEP, nevertheless, showed significant differences for narcoleptics. These were similar to changes described for drowsiness in normals. The AEP, therefore, showed changes related to excessive day time drowsines in narcolepsy-cataplexy when a sensitive performane measure and visual analysis of EEG-polygraphic recordings did not.

Monoaminergic mechanisms and experimental cataplexy

The effects of pharmacological alteration of the monoamine systems were investigated in a canine model of narcolepsy. Cataplexy was quantified in eight severely affected dogs by means of the food-elicited cataplexy test. The specific norepinephrine (NE) uptake blocker nisoxetine, and (to a much lesser extent) the specific serotonin (5-HT) uptake blocker fluoxetine, significantly suppressed cataplexy, as did the tricyclic antidepressants protriptyline, amitriptyline, and chlorimipramine. Thus, experimental cataplexy is suppressed more by inhibition of the uptake of NE than of 5-HT. Methylphenidate, the alpha-adrenoreceptor blocker clonidine, and the dopamine receptor blocker pimozide also suppressed cataplexy in dogs. The beta-adrenergic blocker propranolol, the fatty acid gamma-hydroxybutyrate, and the monoamine oxidase inhibitors clorgyline and pargyline had little or no effect. With one exception (pimozide), all the drugs that suppressed cataplexy are known to be potent suppressors of REM sleep. The suppression of cataplexy induced by nisoxetine or protriptyline was reversed by the anticholinesterase physostigmine, further supporting a postulated aminergic-cholinergic interaction in the mechanisms for cataplexy.

Daytime performance deficits and physiological vigilance in untreated patients with narcolepsy-cataplexy compared to controls

Ten patients, 7 female, 3 male, aged 17-65 years (mean 40) with narcolepsy-cataplexy were compared off treatment to matched controls on 4 performance tests. The tests were the 1 h Wilkinson auditory vigilance task, and 3 shorter tests including the 4-choice serial reaction time, the paced auditory serial addition task (PASAT) and digit span. Tests were counterbalanced and polygraphic recordings were done during all but the 4-choice serial RT. Subjective sleepiness was assessed by the 1-7 levels of the Stanford Sleepiness Scale and effort in the tests by a similar 1-7 scale. Practice sessions were held. Narcoleptics showed poorer performance on the more monotonous tests of auditory vigilance (fewer hits) and the 4-choice serial RT (longer reaction times, more 'gaps'). There were no significant differences between groups on the other performance tests. Narcoleptics were subjectively sleepier during all tests and over-all. But there was no good correlation between perceived degree of sleepiness and performance. They also expressed greater effort to perform the PASAT. The narcoleptics showed greater amounts of drowsiness and light sleep only during the 1 h vigilance test. For the detections of those signals (shorter times) occurring after 13 sec or more of polygraphic wakefulness, narcoleptics performed as well as controls.

An etiology of narcolepsy-cataplexy and a proposed cataplexy neuromechanism

Narcolepsy-cataplexy is an idiopathic sleep disorder that reflects a complex neuropathology. Surveys and physiological investigations indicate that genetic and stress factors are involved in its onset and that stress is associated with symptomatic fluctuations and exacerbations of its clinical course. This paper summarizes the literature regarding the evolution, characteristics and treatment of the disorder. A comprehensive etiology is advanced, integrating neurophysiological and psychological factors specific to narcolepsy-cataplexy with recent advances in blood pressure regulation. Moreover, a testable neuromechanism of cataplexy is proposed, based on longitudinal effects of chronic drowsiness, the strong hypnogenic effect obtained by carotid sinus stimulation, an experimental animal model of narcolepsy-cataplexy, the adaptive characteristics of baroreceptors and, finally, the interconnections between CNS sleep and blood pressure regulators of the brain stem. Through better understanding of the causes and mechanisms of narcolepsy-cataplexy, more effective treatments and preventive measures can be developed, high risk populations identified, and, perhaps, a cure found. Suggestions for future physiological and epidemiological research are made.

Effects of nocturnal gamma-hydroxybutyrate on sleep/waking patterns in narcolepsy-cataplexy

Continuous 48-hour polygraphic recordings of sleep/waking patterns were performed on 14 patients with narcolepsy-cataplexy before and after 7-10 days of treatment of their nocturnal sleep with gamma-hydroxybutyrate (GBH). GBH improved the quality of night sleep by increasing the amount of slow wave sleep, reducing stage I, increasing sleep efficiency (percentage of time in bed spent asleep), and reducing the number of periods of short sleep under 15 minutes. Also nighttime REM sleep was reduced in latency and became less fragmented. The daytime period contained less slow wave sleep and REM sleep, and fewer episodes of prolonged sleep. Patients experienced reduction or loss of daytime attacks of irresistible sleep, cataplectic attacks, and other auxiliary symptoms. Residual daytime drowsiness subsequently improved on low doses of methylphenidate. Tolerance did not develop and there were no serious toxic side-effects. Four of the patients had been refractory to previous combinations of antidepressants and high doses of stimulants.

Multiple sclerosis and narcolepsy/cataplexy in a monozygotic twin

Symptoms of narcolepsy/cataplexy developed in a monozygotic twin at the age of 56 years, 25 years after the onset of multiple sclerosis. The diagnosis of narcolepsy/cataplexy was confirmed by polygraphic recordings demonstrating sleep-onset periods of rapid eye movements (REM), increase in REM time per 24 hours, and disturbed nocturnal sleep. Frequent catapletic attacks were almost completely controlled by clomipramine. These symptoms may constitute one of the paroxysmal syndromes in multiple sclerosis. The discordancy for multiple sclerosis is attributed to a submaximal risk factor in the HLA system and a strong environmental factor in only one of the twins.

Comparison of interwave latencies of brain stem auditory evoked responses in narcoleptics, primary insomniacs and normal controls

A study of brain stem auditory evoked responses (BAER) was carried out in 10 narcoleptics, 10 primary insomniacs and 10 normal controls to determine if a neurophysiologic abnormality could be detected in these primary sleep disorders. The mean interpeak conduction times of Wave I-III, III-V and Iv were compared between the following groups: normal controls awake and in monitored sleep; narcoleptics awake and in monitored sleep, normal controls awake and narcoleptics awake; normal controls awake and insomniacs awake; narcoleptics awake and insomniacs awake; narcoleptics with cataplexy (n = 6) awake and narcoleptics without cataplexy (n = 4) awake. No significant differences were found which suggests that these sleep disorders represent dysfunctions which do not involve brain stem structures subserving the BAER.

Sleep respiratory arrhythmias in control subjects, narcoleptics and non-cataplectic hypersomniacs

Normal subjects may present central-type apneas or periodic respiration during sleep (stages I and II and paradoxical sleep). The importance of these respiratory disorders increases with age. Hypersomniac patients can manifest either similar or more significant sleep respiratory disorders than normal subjects. The presence of cataplexy or obesity does not permit the prediction of the existence of respiratory arrhythmias or of their type. Sleep respiratory arrhythmias of central type are not likely to cause hypersomnia; however, an aggravating role may be played by obstructive apneas.