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2009 Vernet C Convertir en PDF 

Narcolepsy with long sleep time: a specific entity?

Cyrille Vernet and Isabelle Arnulf

 

 Et oui voici mon deuxième papier accepté dans le revue SLEEP

 

Introduction :   Les patients présentant une forme classique de narcolepsie rapportent des épisodes de somnolence irrépressibles (avec ou sans cataplexie), un sommeil de nuit normal ou fragmenté, et font de courtes siestes récupératrices. Cependant, avec l'enregistrement polysomnographique de longue durée, nous avons identifié des patients narcoleptiques ressemblant aux patients atteints d'hypersomnie idiopathique.

Objectif : Le but de cet article est d'isoler et de décrire un nouveau sous-type de patients narcoleptiques avec long temps de sommeil.

Sujets : Sur l'ensemble des 160 patients narcoleptiques nouvellement diagnostiqués ces 3 dernières années, 29 (18%) avaient un temps de sommeil allongé (plus de 11h / 24h).

interventions : Les patients et les témoins ont bénéficié d'un interrogatoire face à face, d'un génotypage HLA et d'un enregistrement polysomnographique de 48 heures incluant les tests itératifs de latence d'endormissement (TILE) et un enregistrement de longue durée.

Analyse : Nous avons comparé les patients narcoleptiques avec (n=23) et sans (n=29) long temps de sommeil avec 25 patients atteints d'hypersomnie idiopathique et 20 témoins sains.

Résultats : Par rapport aux patients narcoleptiques avec un temps de sommeil normal, les narcoleptiques avec un temps de sommeil allongé avaient une durée de maladie similaire, ainsi qu'une même fréquence de patients cataplectiques, de paralysies du sommeil, d'hallucinations, une latence moyenne d'endormissement au TILE raccourcie, la présence de plusieurs endormissements en sommeil paradoxal au TILE et une positivité au génotype HLA DQB1*0602.

Cependant ils avaient un temps de sommeil plus long sur 24 heures, une plus grande efficacité de sommeil, un score de somnolence inférieur, et plus souvent des siestes non récupératrices. Seulement 3/23 d'entre eux avaient une narcolepsie classique complète (HLA positif et présence de cataplexies).

Conclusions :Ce sous groupe de narcoleptiques avec un temps de sommeil allongé représente 18% des narcoleptiques. Leurs symptômes recouvrent à la fois les difficultés des narcoleptiques (très forte somnolence) et des patients hypersomniaques (temps de sommeil nocturne allongé et siestes longues non récupératrices). Ainsi ces patients pourraient présenter plusieurs dysfonctionnements des systèmes d'éveils.

 

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Résumé en anglais

Background: The classical narcolepsy patient reports intense feelings of sleepiness (with/out cataplexy), normal or disrupted night-time sleep, and takes short and restorative naps. However, with long-term monitoring, we identified some narcoleptics resembling patients with idiopathic hypersomnia.

Objective:  To isolate and describe a new subtype of narcolepsy with long sleep time.

Setting: University Hospital

Design: Controlled, prospective cohort

Participants: Out of 160 narcoleptics newly diagnosed within the past 3 years, 29 (18%) had a long sleep time (more than 11 hr/24 hr). We compared narcoleptics with (n=23) and without (n=29) long sleep time to 25 hypersomniacs with long sleep time as well as to 20 healthy subjects.

Intervention: Patients and controls underwent face-to face interviews, questionnaires, human leukocyte antigen genotype (HLA), an overnight polysomnography, multiple sleep latency tests, and 24-hour ad libitum sleep monitoring.

Results: Narcoleptics with long sleep time had a similar disease course, and evidenced similar frequencies of cataplexy, sleep paralysis, hallucinations, multiple sleep onset in REM periods, short mean sleep latencies and HLA DQB1*0602 positivity as narcoleptics with normal sleep time did. However, they had longer sleep time during 24 hours, and higher sleep efficiency, lower Epworth sleepiness score and more often unrefreshing naps. Only 3/23 had a ‘core’ narcolepsy (HLA and cataplexy positive).

Conclusions:  The subgroup of narcoleptics with a long sleep time comprises 18% of narcoleptics. Their symptoms combine the disabilities of both narcolepsy (severe sleepiness) and idiopathic hypersomnia (long sleep time and unrefreshing naps). Thus, they may constitute a group with multiple arousal system dysfunctions.

 

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Article complet en anglais

 

Introduction

 

The clinical symptoms of narcolepsy include chronic, severe, objective daytime sleepiness with multiple daytime sleep onset REM periods. These markers are associated, to various extents, with REM sleep-associated phenomena (i.e., cataplexy, hypnagogic hallucinations, sleep paralysis, REM sleep behavior disorders), disturbed nocturnal sleep, periodic leg movements, depressive mood and increased weight.1 During the night, the most specific feature of nocturnal sleep is a REM sleep period at sleep onset, which is observed in only 25% of patients during the first monitored night. In addition, sleep efficiency in narcoleptics tends be lower than in controls.3  Up to 71% narcoleptics are unable to sleep without awakening, and 83% complain of early awakenings (see a review in 2). Recently, much emphasis has been placed on the frequent night-time awakenings, which may follow an ultradian rhythm in narcoleptics. The existence of narcoleptic dyssomnia has, in part, led to the recent treatment of sodium oxybate given before and during sleep in narcoleptics, as a means to obtaining a more continuous and deep sleep. It also helps alleviate cataplexy and daytime sleepiness.

Disrupted night-time sleep in human narcolepsy parallels the fragmented non-REM sleep observed in Dobermans with genetically abnormal hypocretin-2 receptor, though the total duration of sleep is not different from control dogs.4 In murine narcolepsy, sleep episodes are similarly fragmented, though the total time asleep in these transgenic animals (823 min) is not significantly different from the 783 min observed in wild animals.5 In human narcolepsy, total sleep time was initially measured during a 24-hour period, before the development of the multiple sleep latency test.6 Sleep duration was not found to be different between narcoleptics patients and controls, as because daytime naps were balanced by ultradian intra-sleep awakenings in narcoleptic patients.7 Combined, these results led to the primary theory of sleep-state instability in narcolepsy, which refers to a difficulty in consolidating either wakefulness (that is, an inability to maintain wakefulness over long periods of the daytime) or sleep (referring to an inability to maintain continuous sleep, with frequent awakening). As narcolepsy is primarily caused by hypocretin deficiency, it has been hypothesized that hypocretin could stabilize the wake-sleep switches.8

Although most narcoleptics fit this framework (that is, they generally show disrupted sleep and short, restorative naps), we observed in our clinical practice a subgroup of patients with narcolepsy who reported abnormally long night-time sleep, with feelings of sleep drunkenness and unrefreshing long naps. These clinical features were similar to those observed in idiopathic hypersomnia with long sleep time. Idiopathic hypersomnia is now further divided into hypersomnia with and without long sleep time.9 Hypersomnia with long sleep time is characterized by a prolonged (>10 hr) night-time sleep, with frequent sleep drunkenness and long, unrefreshing naps, reaching usually more than 11-12 hrs asleep per day. Recently, we found that hypersomniacs (and no healthy controls) slept longer than 11 hrs when monitored continuously during night and day.10 Hypersomnia without long sleep time is characterized by normal (<10 hr) sleep time, short (<8 min) mean daytime latency during multiple sleep latency tests (MSLT) and fewer than two sleep onset in REM periods (SOREMPs). This recent category, resembling narcolepsy without REM sleep-associated abnormalities, has been isolated after studying a group of patients with idiopathic hypersomnia.11 Here, we systematically studied the narcoleptics with long sleep time (>11 hr /24 hr) and contrasted them with patients suffering a classical narcolepsy and patients suffering from idiopathic hypersomnia with long sleep time.

 

Methods

 Subjects

 Between 2005 and 2008, all (n=900) patients referred for excessive daytime sleepiness without sleep-disordered breathing (pre-checked by respiratory polygraphy) underwent the same, routine 48 hour protocol (see below) in the sleep disorders unit, a tertiary care university hospital with a biased over-recruitment of neurological cases. In this series, we identified patients with hypersomnias of central origin who met the following inclusion criteria: (1) complaints of excessive daytime sleepiness occurring daily for at least three months; and (2) no improvement with an increase of the nighttime length for 15 days; and (3) a mean sleep latency (MSL) during multiple sleep latency tests (MSLT) lower than 8 minutes; or (4) a total sleep time > 10 hours (600 min) during night-time sleep monitoring. We excluded the patients with: (1) sleep-disordered breathing, defined by a respiratory disturbance index greater than 10 per hour (this index included apnea, hypopnea, and respiratory effort related arousal events; flow limitation was measured on the nasal canulae, and threshold was set at a minimum of five apnea/hour); and (2) narcolepsy due to a medical condition (e.g. Parkinson’s disease, lupus, genetic disease, depression); and (3) hypersomnia due to drug or substance use. No patient received any psychotropic drug during the period of sleep monitoring. In previously treated patients, special care was paid to withdraw any psychotropic drugs for at least 15 half-lives. In this group of 312 consecutive patients with hypersomnia of central origin, we identified 160 patients with narcolepsy, based on classical criteria (that is, with a mean sleep latency during multiple sleep latency tests lower than 8 minutes and more than one sleep-onset REM period or clear-cut cataplexy).9 Among these 160 narcoleptics, we isolated 29 (18.1%) patients with a diagnosis of narcolepsy and long sleep time (that is, with a total sleep time greater than 11 hours during 24-hour, long-term sleep monitoring). Among these 29 patients, only 23 had fully completed the various clinical measures. We contrasted their clinical, demographical and polygraphical characteristics with a random sample of 29 patients demonstrating a classical narcolepsy (short MSLT, multiple SOREMPs or cataplexy), and with 25 randomly selected patients with idiopathic hypersomnia with long sleep time (defined as with no more than one SOREMPs during MSLT and a total sleep time > 11 hours on 24 hour sleep monitoring). Using a threshold of 11 hours to define long sleep time was previously piloted while monitoring 35 healthy volunteers during the 48-hour long procedure.11 In the International Classification of Sleep Disorders-revised, a cut-off of 10 hours night-time sleep and daytime sleepiness is used for defining hypersomnia with long sleep time, while more than 11-12 hours of total sleep per 24 hours is indicated as a typical finding when long term sleep monitoring are performed in patients with hypersomnia with long sleep time.

Twenty healthy subjects volunteered to take part as controls after recruitment by advertisement. They were matched by age and sex with the group of narcoleptics with long sleep time. The subjects were selected after a medical interview for having no complaints regarding their sleep, no excessive daytime sleepiness (defined as the absence of spontaneous or elicited complaint and also having a score at the Epworth sleepiness scale lower than 11), no chronic sleep deprivation (determined using a questionnaire on sleep habit), no shift or night work, no severe medical illness, and no use of medications known to modify sleep and wakefulness. The control group took part to the 48-hour sleep protocol. Control subjects were able to comply adequately with the study requirements, signed an informed consent and were paid. The study was approved by the local ethics committee.

 

Investigations

 Participants were instructed to follow a regular sleep-wake rhythm, with at least 8 hours in bed during the week preceding the 48 hour-long investigations in the Sleep Disorders Unit. They underwent a face to face interview about sleep symptoms (cataplexy, sleep drunkenness, sleep paralysis, restorative naps) and completed a standardized comprehensive sleep questionnaire including the Epworth sleepiness scale,12 the Horne-Ostberg eveningness-morningness scale,13 the Pichot fatigue scale,14 the Fatigue Severity Score,15 and the hospital depression and anxiety (HAD) rating scale.16 The class-II human leukocyte antigen (HLA) genotype was determined for all patients and controls.  The sleep and wake monitoring procedure included (i) a habituation night with sleep and respiratory monitoring from 11 pm to 6:30 am, followed the next day by (ii) five standard sleep latency tests (MSLT) at 8 am, 10 am, noon, 2 pm, 4 pm, that were terminated after 20 minutes if no sleep occurred, and after 15 min asleep if sleep occurred 17; and (iii) followed the next evening by a long term (24-hour) sleep monitoring. The aim of the long term sleep monitoring was to elicit the maximum spontaneous amount of sleep in relaxed and quiet, but not totally abnormal conditions, while any sleep episode, whether at night or during daytime, was never be interrupted by the technicians. Controls and patients were already in the sleep unit for 24 hours. They received dinner at 7 pm. TV, computer, and visit from friends were forbidden, but books, newspapers, watches and daylight were allowed. After 9 pm, the participants were free to determine when they wanted switch lights off for the evening, and were allowed to sleep until they spontaneously awakened (and turned lights on) the next day. In addition, all subjects were asked to lay down in the dark for two naps during the morning and the afternoon. The nap attempts were discontinued by the subjects after 30 min if they could not sleep, and were continued ad libitum when they fell asleep. Tests were stopped at 5 pm the last day. In total, this procedure provided a 20-hour long opportunity to sleep for all subjects. Subjects received a breakfast after waking up, and a lunch if they woke up for. This procedure is highly recommended in order to diagnose idiopathic hypersomnia,9, 18 but does not yield standardized values for healthy subjects. As part of our current study, we present normative values here.

Polysomnographic recordings included an electroencephalography (Fp1-A2, C3-A2, O1-A2), left and right electro-oculograms, levator menti and bilateral tibialis anterior surface electromyography, nasal pressure trough cannulae, respiratory efforts using thoracic and abdominal belts, position, tracheal sounds, pulse rate and transcutaneous oximetry (Medatec Ltd France) during the first night. The respiratory sensors were removed during the MSLT and the 24-hour sleep monitoring. Sleep stages, arousals, periodic leg movements, and respiratory events were scored visually according to standard criteria.19-22 The total sleep time, total sleep period, sleep and REM sleep latencies, the durations and percentages of non REM sleep stage 1, 2, 3-4, and REM sleep were determined during Night 1 and Night 2, and during the 24-hour monitoring procedure. The indexes of sleep fragmentation (that is, the arousal index, periodic leg movements, periodic leg movement-associated arousal index, and apnea-hypopnea index), and minimal oxygen saturation during sleep were measured during Night 1. In order to determine whether it was correlated with sleep drunkenness, we noted the time of offset of the last slow wave sleep (SWS) episode that lasted longer than 5 minutes during the second night sleep.

 

Statistical analysis

 The patients with narcolepsy with long sleep time were compared as a group to each of the other studied groups, in order to determine whether they are more similar to those with classical narcolepsy or those with idiopathic hypersomnia with long sleep time. We analyzed our between-group dichotomous variables using chi-square tests, and analyzed our continuous variables using analysis of variance (Statistica 7.1, Stat Soft Inc, Tulsa, OK). A p value less than 0.05 was considered to be significant (with corrections for repeated measures). Values are presented as mean ± SD (unless otherwise specified).


 

Results

Clinical differences between narcoleptics with long sleep time and other groups

Among these 160 narcoleptics, we isolated 29 (18.1%) patients with a diagnosis of narcolepsy with long sleep time (that is, with a total sleep time greater than 11 hours on 24-hour, long-term sleep monitoring). None of these participants had a personal or family history of long sleeper prior to the sleepiness onset. Their demographic and clinical characteristics, compared to other participant groups are summarized in Table 1. The age, body mass index and sex ratio of narcoleptics with long sleep time did not differ from controls (as expected by the matching procedure), nor did these differ from classical narcoleptics. The age at symptom onset was similar in the narcoleptics with (18.1±5.3 y) and without (19.9±6.2 y, P=0.46) long sleep time. At the time of the polysomnography, the disease course was similar in narcoleptics with (9±8 y, range: 1-21 y) and without (8±8 y, range: 1-24 y, P=0.77) long sleep time.

 

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Hypnagogic hallucinations, cataplexy, sleep paralysis, as well as sleep drunkenness and HLA DQB1*0602 positivity were as frequent in narcoleptics with and without long sleep time, but the naps were more frequently unrefreshing in the narcoleptics with long sleep time, and the Epworth sleepiness score was lower.  All these symptoms (except cataplexy), were observed in the group of patients with idiopathic hypersomnia with long sleep time, but not in the controls. As for what can be defined as ‘core narcolepsy’ (i.e. the association in the same patient of clear cut cataplexy, short MSL, multiple SOREMPs and HLA positivity), there were 3/23 (13%) patients with ‘core narcolepsy’ in the group of narcoleptics with long sleep time, and 7/29 (24%) in the group of narcolepsy without long sleep time. These percentages were not different. The demographical, clinical and sleep characteristics of this subgroup is displayed in the Supplementary Table A. Sleepiness and fatigue scores were similar for the three patient groups, and all three patient groups scored higher than those in the control group did. The same pattern was observed for anxiety and depression scores, which were slightly higher in patients than in controls. As evidenced by their Horne-Ostberg scores, narcoleptics with long sleep time had a more advanced sleep phase than patients with idiopathic hypersomnia, but were not different from controls and from other narcoleptics.

 

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Polysomnographic differences between narcoleptics with long sleep time and other groups

 The polysomnographic measures for all groups are displayed in Table 2. As expected, night-time sleep time was two-hours longer in narcoleptics with long sleep time than those without, was one hour and 30 minute longer than for control subjects, but was 50 min shorter than for patients with idiopathic hypersomnia. Accordingly, this difference corresponded to one additional sleep cycle in narcoleptics with long sleep time and hypersomniacs, as compared to the other groups, while sleep cycle durations were similar across all groups. Sleep efficiency was higher in narcoleptics with (92.4%) than without long sleep time (87.1 %, P=0.04). In all groups, sleep onset latency was similar, though REM sleep latency was shorter in narcoleptics than in controls. As concerns sleep architecture, there were no differences between narcoleptics with long sleep time and any other group for the percent of sleep stages 1, 2, 3-4 and REM sleep. All groups contained similar numbers of subjects with slow wave sleep after 6 am, though the last slow wave sleep episode for the narcolepsy with long sleep time group occurred later than in controls, and earlier than in patients with idiopathic hypersomnia. As concerns sleep fragmentation and movements, narcoleptics with long sleep time did not differ from other patient groups, but had less arousals and more frequent periodic leg movements than did controls. The respiratory disturbances indexes were generally low and were not different between groups.

 

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During the multiple sleep latency tests, the mean sleep latency was shorter in narcoleptics (whether they had or not a long sleep time) than in hypersomniacs or control subjects. There were as many SOREMPS in narcoleptics with and without long sleep time.

 

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During the 24 hour-long sleep monitoring, daytime sleep time was longer in narcoleptics with long sleep time than in all other groups. On a 24-hour basis, narcoleptics with long sleep time (as expected) produced longer sleep amounts than the other narcoleptics or the controls, with a mean sleep amount of 738 ± 58  min (12.3 hours, range:11-14.5 hours), similar to the total sleep of patients with idiopathic hypersomnia (that is, with no change in the breakdown of sleep stages). That is, narcoleptics with long sleep time slept 3 hours more per 24 hr than the other narcoleptics. An example of 24 hour-long sleep hypnogram in patients with narcolepsy/cataplexy with and without long sleep time is displayed in Figure 1.

 

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If one isolates the narcoleptics sleeping more than 10 hours per night, they represent only 12/23 patients. Except they were younger (23.8 ± 6.7 y) than the other narcoleptics (31.2 ± 10.1 y, P=0.03, a difference not seen when the threshold for long sleep time is 11hr/24r), the differences with the three other groups were similar to what we found before (supplementary Tables B and C). Compared to other narcoleptics, they had a longer sleep at night and during 24 hr monitoring, with a higher sleep efficiency. Compared to controls, they had more frequently HLA positivity and hypnagogic hallucinations, and higher subjective scores of sleepiness, fatigue, anxiety and depression. Compared to patients with idiopathic hypersomnia, they had higher Horne-Ostberg scores.

 

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As a spinal tap is not considered a routine procedure for the diagnosis of narcolepsy when it is possible by other means, we could gather only a single measure of cerebrospinal hypocretin-1. This procedure was performed in Stanford University in one of our narcoleptic patients with no typical cataplexy and long sleep time. The hypocretin-1 level was undetectable (that is, it was lower than 40 pg/mL). 

 

Discussion

The subgroup of narcoleptics with long sleep time represents 18% of a consecutive series of narcoleptics in a tertiary sleep disorders unit. This subgroup shares many similarities with classical narcolepsy (namely, similar rates of cataplexy, sleep paralysis, hypnagogic hallucinations, short daytime mean sleep latency with multiple sleep onset in REM periods, and half were HLA positive). This group, however, has per definition, longer sleep time during the night and day, with higher sleep efficiencies. As for the increased sleep amounts, this group most resembles the patients with idiopathic hypersomnia and long sleep time, with both groups sleeping a mean 12 hours per day. The three patient groups have similarly high scores of sleepiness and fatigue, and mild scores of anxiety and depression, which clearly differentiate them from healthy controls.

            One may object that narcoleptics with long sleep time could be some former long sleepers that later developed narcolepsy, and hence present with a mixture of a physiological trait (long sleeper) and disease (narcolepsy). This is not the case here, as our patients had no previous personal or family history of long sleep time. Acute recent onset narcolepsy has been occasionally associated with increased sleep amount, especially in children.23 However, in our series, there were no children or patients with recent onset (lower than 1 year) narcolepsy, and no different disease course between narcoleptics with and without long sleep time was observed. This suggests that the long sleep time phenotype may last beyond the first years of disease. 

            In the past, several groups concluded that narcoleptics fail to demonstrate an excess need for sleep when given a chance to sleep uninterrupted for 24 hours.7, 24 In contrast, one patient with narcolepsy slept 17 hours during a 24-hour sleep monitoring, while three other narcoleptics slept more than 11 hours in a series of 8 narcoleptics monitored during bed rest.25 In a large study of 157 Italian patients with narcolepsy, narcoleptics declared to sleep one hour more (per 24 hours) than the controls, with standard deviations suggesting that some of them would sleep more than 11 hours.26 The occasional presence of narcoleptics with sleep drunkenness and unrefreshing naps has not been totally overlooked in the history of narcolepsy. Daniels early stated that “Although patients with narcolepsy are usually fresher early in the morning than during the remainder of the day, some become very drowsy shortly after arising from a good night’s rest; an unusually long night’s sleep may even increase the diurnal drowsiness.”27 In a group of 41 patients with narcolepsy/cataplexy, 59% did not feel

refreshed in the morning, 39% had an incomplete awakening suggestive of sleep drunkenness, while 5% had non-refreshing naps.28 The possibility of isolating a group of narcoleptics with long sleep time is of both clinical and pathophysiological interest. Narcoleptics with long sleep time may have more daytime problems than patients with classical narcolepsy do, because they share the main features of narcolepsy, but have additional difficulties waking up refreshed, being on time at work or at school in the morning, and do not benefit from short, refreshing naps. In our experience, they are the most difficult to treat, although this aspect was not formally addressed in this paper.

            The main limitation of this series is the absence of measure of the CSF hypocretin-1 levels, except in one narcoleptic. Though this narcoleptic was hypocretin-1 deficient and had a long sleep time, we cannot yet determine how many narcoleptics with long sleep time are also hypocretin-1 deficient; further research is required. As hypocretin-1 is deficient in 88-93% of narcoleptics with clear-cut cataplexy, HLA positivity, and no family history of narcolepsy,29,30 it has been suggested that these clinical and biological characteristics define a homogenous subgroup of ‘core narcolepsy’. This ‘core narcolepsy’ is however also found in 13 % of patients with long sleep time. The pathophysiology of the ‘narcolepsy with long sleep time’ phenotype is unknown, as is the cause of idiopathic hypersomnia, which challenges our concept of hypocretin as consolidating the sleep-wake transitions. Hypocretin-deficient animals do not, however, display increased amounts of sleep, suggesting that additional deficits in arousal systems must be necessary for developing a true ‘hypersomnia’. Animals with double invalidation of genes coding for neurotransmitters involved in regulating arousal (e.g., hypocretin and histamine) could be useful for investigating these hypotheses. Our patients may potentially have a double dysfunction in their arousal systems. The observation of long sleep time during acute onset narcolepsy, disappearing years after, suggests that some (but not all) patients compensate for this deficit, with differences being potentially dependent on their genetics. Furthermore, recent measures of CSF histamine levels in narcoleptics, controls and patients with idiopathic hypersomnia suggest that the histamine arousal systems can also be deficient in some of these subjects.30,31 Anyway, demographical and clinical data on sleep excess, as well as animal models with excess sleep amounts, are yet lacking.32

            After the recent sleep disorders reclassification, the narcolepsy/hypersomnia landscape is becoming richer with the addition of syndromes previously considered as atypical, including narcolepsy without cataplexy and hypersomnia without long sleep time (which resembles narcolepsy, but does not involve REM sleep abnormalities). Mirroring this subgroup, narcolepsy with long sleep time resembles idiopathic hypersomnia with long sleep time but contains numerous REM sleep abnormalities. To illustrate this concept, we suggest a table classifying the four groups, depending on sleep time, MSLT results and SOREMPs (Table 3). Patients suffering this form of narcolepsy are more disabled than others, with shorter mean sleep latencies and a trend for more frequent sleep drunkenness and unrefreshing naps; hence, they may comprise a clinical spectrum that deserves specific medical attention.

 

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