Prevalence and Course of Idiopathic Hypersomnia in the Wisconsin Sleep Cohort Study.

BACKGROUND AND OBJECTIVES: Idiopathic hypersomnia (IH) is a CNS disorder of hypersomnolence of unknown etiology. Due to the requirement for objective sleep testing to diagnose the disorder, there are currently no population-based estimates of the prevalence of IH nor data regarding the longitudinal course of IH in naturalistic settings. METHODS: Subjective and objective data from the Wisconsin Sleep Cohort study were used to identify cases with probable IH from participants with polysomnography and multiple sleep latency test data. Demographic, polysomnographic, and symptom-level data were compared between those with and without IH. Longitudinal trajectories of daytime sleepiness among those with IH were assessed to evaluate symptom persistence or remission over time. RESULTS: From 792 cohort study participants with available polysomnography and multiple sleep latency test data, 12 cases with probable IH were identified resulting in an estimated prevalence of IH of 1.5% (95% CI 0.7-2.5, p < 0.0001). Consistent with inclusion/exclusion criteria, cases with IH had more severe sleepiness and sleep propensity, despite similar or longer sleep times. Longitudinal data (spanning 12.1 ± 4.3 years) demonstrated a chronic course of sleepiness for most of the cases with IH, though pathologic somnolence remitted in roughly 40% of cases. DISCUSSION: These results demonstrate IH is more common in the working population than generally assumed with a prevalence on par with other common neurologic and psychiatric conditions. Further efforts to identify and diagnose those impaired by unexplained daytime somnolence may help clarify the causes of IH and the mechanisms underlying symptomatic remission.

Idiopathic hypersomnia years after the diagnosis.

Little attention has been paid to the long-term development of idiopathic hypersomnia symptoms and idiopathic hypersomnia comorbidities. The aim of this study was to describe the general health of patients with idiopathic hypersomnia years after the initial diagnosis, focusing on current subjective hypersomnolence and the presence of its other possible causes. Adult patients diagnosed with idiopathic hypersomnia ≥ 3 years ago at sleep centres in Prague and Kosice were invited to participate in this study. A total of 60 patients were examined (age 47.3 ± SD = 13.2 years, 66.7% women). In all participants, their hypersomnolence could not be explained by any other cause but idiopathic hypersomnia at the time of diagnosis. The mean duration of follow-up was 9.8 + 8.0 years. Fifty patients (83%) reported persisting hypersomnolence, but only 33 (55%) had no other disease that could also explain the patient's excessive daytime sleepiness and/or prolonged sleep. In two patients (3%), the diagnosis in the meantime had changed to narcolepsy type 2, and 15 patients (25%) had developed a disease or diseases potentially causing hypersomnolence since the initial diagnosis. Complete hypersomnolence resolution without stimulant treatment lasting longer than 6 months was reported by 10 patients (17%). To conclude, in a longer interval from the diagnosis of idiopathic hypersomnia, hypersomnolence may disappear or may theoretically be explained by another newly developed disease, or the diagnosis may be changed to narcolepsy type 2. Thus, after 9.8 years, only 55% of the examined patients with idiopathic hypersomnia had a typical clinical picture of idiopathic hypersomnia without doubts about the cause of the current hypersomnolence.

Idiopathic hypersomnia and Kleine-Levin syndrome.

Idiopathic hypersomnia (IH) and Kleine-Levin syndrome (KLS) are rare disorders of central hypersomnolence of unknown cause, affecting young people. However, increased sleep time and excessive daytime sleepiness (EDS) occur daily for years in IH, whereas they occur as relapsing/remitting episodes associated with cognitive and behavioural disturbances in KLS. Idiopathic hypersomnia is characterized by EDS, prolonged, unrefreshing sleep at night and during naps, and frequent morning sleep inertia, but rare sleep attacks, no cataplexy and sleep onset in REM periods as in narcolepsy. The diagnosis requires: (i) ruling out common causes of hypersomnolence, including mostly sleep apnea, insufficient sleep syndrome, psychiatric hypersomnia and narcolepsy; and (ii) obtaining objective EDS measures (mean latency at the multiple sleep latency test≤8min) or increased sleep time (sleep time>11h during a 18-24h bed rest). Treatment is similar to narcolepsy (except for preventive naps), including adapted work schedules, and off label use (after agreement from reference/competence centres) of modafinil, sodium oxybate, pitolisant, methylphenidate and solriamfetol. The diagnosis of KLS requires: (i) a reliable history of distinct episodes of one to several weeks; (ii) episodes contain severe hypersomnia (sleep>15h/d) associated with cognitive impairment (mental confusion and slowness, amnesia), derealisation, major apathy or disinhibited behaviour (hypersexuality, megaphagia, rudeness); and (iii) return to baseline sleep, cognition, behaviour and mood after episodes. EEG may contain slow rhythms during episodes, and rules out epilepsy. Functional brain imaging indicates hypoactivity of posterior associative cortex and hippocampus during symptomatic and asymptomatic periods. KLS attenuates with time when starting during teenage, including less frequent and less severe episodes. Adequate sleep habits, avoidance of alcohol and infections, as well as lithium and sometimes valproate (off label, after agreement from reference centres) help reducing the frequency and severity of episodes, and IV methylprednisolone helps reducing long (>30d) episode duration.

Comorbid parasomnias in narcolepsy and idiopathic hypersomnia: more REM than NREM parasomnias.

STUDY OBJECTIVES: To assess the frequency, determinants, and clinical impact of clinical rapid eye movement (REM) and non-REM (NREM) parasomnias in adult patients with narcolepsy type 1 (NT1), narcolepsy type 2 (NT2), and idiopathic hypersomnia compared with healthy controls. METHODS: Familial and past and current personal parasomnias were assessed by questionnaire and medical interviews in 710 patients (220 NT1, 199 NT2, and 221 idiopathic hypersomnia) and 595 healthy controls. RESULTS: Except for sleep-related eating disorder, current NREM parasomnias were rare in all patient groups and controls. Sleep-related eating disorder was more frequent in NT1 patients (7.9% vs 1.8% in NT2 patients, 2.1% in patients with idiopathic hypersomnia, and 1% in controls) and associated with disrupted nighttime sleep (odds ratio = 3.9) and nocturnal eating in full awareness (odds ratio = 6.9) but not with sex. Clinical REM sleep behavior disorder was more frequent in NT1 patients (41.4%, half being violent) than in NT2 patients (13.2%) and affected men more often than women (odds ratio = 2.4). It was associated with disrupted nighttime sleep, depressive symptoms, and antidepressant use. Frequent (> 1/week) nightmares were reported by 39% of patients with NT1, 29% with NT2, and 27.8% with idiopathic hypersomnia (vs 8.3% in controls) and were associated with depressive symptoms in narcolepsy. No parasomnia (except sleep-related hallucinations) worsened daytime sleepiness. CONCLUSIONS: In patients with central disorders of hypersomnolence, comorbid NREM parasomnias (except for sleep-related eating disorder) are rare and do not worsen sleepiness. In contrast, REM parasomnias are prevalent (especially in NT1) and are associated with male sex, disrupted nighttime sleep, depressive symptoms, and antidepressant use. CITATION: Leu-Semenescu S, Maranci J-B, Lopez R, et al. Comorbid parasomnias in narcolepsy and idiopathic hypersomnia: more REM than NREM parasomnias. J Clin Sleep Med. 2022;18(5):1355-1364.

Sleeping through a pandemic: impact of COVID-19-related restrictions on narcolepsy and idiopathic hypersomnia.

STUDY OBJECTIVES: To assess the impact of coronavirus disease 2019 (COVID-19)-related restrictions on narcolepsy type 1 (NT2), narcolepsy type 2 (NT2), and idiopathic hypersomnia (IH). METHODS: Participants with NT1, NT2, and IH followed in a university hospital completed an online 78-question survey assessing demographic, clinical, and occupational features of the population during the first COVID-19-related lockdown. RESULTS: A total of 219 of 851 (25.7%) respondents of the survey reported a mean increase of 1.2 ± 1.9 hours (P < .001) in night sleep time and a mean decrease of 1.0 ± 3.4 points (P < .001) on the Epworth Sleepiness Scale during lockdown. Bedtime was delayed by 46.1% of participants and wakeup time was delayed by 59.6%, driven primarily by participants with IH. Teleworkers (but not in-person workers) reported a mean increase of 0.9 ± 1.2 hours in night sleep (P < .001) and a mean decrease in sleepiness score of 1.6 ± 3.1 (P < .001). Cataplexy improved in 54.1% of participants with NT1. Sleepiness correlated with psychological wellness (r = .3, P < .001). As many as 42.5% enjoyed the lockdown, thanks to reallocation of time usually spent commuting toward longer sleep time, hobbies, and family time, and appreciated a freer napping schedule. Conversely, 13.2% disliked the lockdown, feeling isolation and psychological distress. CONCLUSIONS: Extended sleep time, circadian delay (in patients with IH), and teleworking resulted in decreased symptoms of central hypersomnias. These findings suggest that people with IH, NT1, and NT2 may benefit from a decrease in social and professional constraints on sleep-wake habits, and support advocacy efforts aimed at facilitating workplace and schedule accommodations for this population. CITATION: Nigam M, Hippolyte A, Dodet P, et al. Sleeping through a pandemic: impact of COVID-19-related restrictions on narcolepsy and idiopathic hypersomnia. J Clin Sleep Med. 2022;18(1):255-263.

Effectiveness and side-effect profile of stimulant therapy as monotherapy and in combination in the central hypersomnias in clinical practice.

Effectiveness and side-effect profile data on pharmacotherapy for daytime sleepiness in central hypersomnias are based largely upon randomized controlled trials. Evidence regarding the use of combination therapy is scant. The aim of this study was to examine the effectiveness and occurrence of drug-related side effects of these drugs in routine clinical practice. Adult patients diagnosed with a central hypersomnia during a 54-month period at a tertiary sleep disorders centre were identified retrospectively. Side effects were recorded at every follow-up visit. A total of 126 patients, with 3275 patient-months of drug exposure, were categorized into narcolepsy type 1 (n = 70), narcolepsy type 2 (n = 47) and idiopathic hypersomnia (n = 9). Modafinil was the most common drug used as a first-line treatment (93%) and in combination therapy (70%). Thirty-nine per cent of the patients demonstrated a complete, 25% partial and 36% a poor response to treatment. Combination treatment improved daytime sleepiness in 55% of the patients with residual symptoms despite monotherapy. Sixty per cent of patients reported side effects, and 30% reported treatment-limiting side effects. Drugs had similar side-effect incidence (P = 0.363) and their side-effect profile met those reported in the literature. Twenty-seven per cent of the patients received combination treatment and had fewer side effects compared to monotherapy (29.4% versus 60%, respectively, P = 0.001). Monotherapy appears to achieve satisfactory symptom control in most patients with central hypersomnia, but significant side effects are common. Combination therapy appears to be a useful and safe option in patients with refractory symptoms.

French consensus. Idiopathic hypersomnia: Investigations and follow-up.

Idiopathic hypersomnia is a rare, central hypersomnia, recently identified and to date of unknown physiopathology. It is characterised by a more or less permanent, excessive daytime sleepiness, associated with long and unrefreshing naps. Night-time sleep is of good quality, excessive in quantity, associated with sleep inertia in the subtype previously described as "with long sleep time". Diagnosis of idiopathic hypersomnia is complex due to the absence of a quantifiable biomarker, the heterogeneous symptoms, which overlap with the clinical picture of type 2 narcolepsy, and its variable evolution over time. Detailed evaluation enables other frequent causes of somnolence, such as depression or sleep deprivation, to be eliminated. Polysomnography and multiple sleep latency tests (MSLT) are essential to rule out other sleep pathologies and to objectify excessive daytime sleepiness. Sometimes the MSLT do not show excessive sleepiness, hence a continued sleep recording of at least 24hours is necessary to show prolonged sleep (>11h/24h). In this article, we propose recommendations for the work-up to be carried out during diagnosis and follow-up for patients suffering from idiopathic hypersomnia.

Smoking, Alcohol, Drug Use, Abuse and Dependence in Narcolepsy and Idiopathic Hypersomnia: A Case-Control Study.

STUDY OBJECTIVES: Basic experiments support the impact of hypocretin on hyperarousal and motivated state required for increasing drug craving. Our aim was to assess the frequencies of smoking, alcohol and drug use, abuse and dependence in narcolepsy type 1 (NT1, hypocretin-deficient), narcolepsy type 2 (NT2), idiopathic hypersomnia (IH) (non-hypocretin-deficient conditions), in comparison to controls. We hypothesized that NT1 patients would be less vulnerable to drug abuse and addiction compared to other hypersomniac patients and controls from general population. METHODS: We performed a cross-sectional study in French reference centres for rare hypersomnia diseases and included 450 adult patients (median age 35 years; 41.3% men) with NT1 (n = 243), NT2 (n = 116), IH (n = 91), and 710 adult controls. All participants were evaluated for alcohol consumption, smoking habits, and substance (alcohol and illicit drug) abuse and dependence diagnosis during the past year using the Mini International Neuropsychiatric Interview. RESULTS: An increased proportion of both tobacco and heavy tobacco smokers was found in NT1 compared to controls and other hypersomniacs, despite adjustments for potential confounders. We reported an increased regular and frequent alcohol drinking habit in NT1 versus controls but not compared to other hypersomniacs in adjusted models. In contrast, heavy drinkers were significantly reduced in NT1 versus controls but not compared to other hypersomniacs. The proportion of patients with excessive drug use (codeine, cocaine, and cannabis), substance dependence, or abuse was low in all subgroups, without significant differences between either hypersomnia disorder categories or compared with controls. CONCLUSIONS: We first described a low frequency of illicit drug use, dependence, or abuse in patients with central hypersomnia, whether Hcrt-deficient or not, and whether drug-free or medicated, in the same range as in controls. Conversely, heavy drinkers were rare in NT1 compared to controls but not to other hypersomniacs, without any change in alcohol dependence or abuse frequency. Although disruption of hypocretin signaling in rodents reduces drug-seeking behaviors, our results do not support that hypocretin deficiency constitutes a protective factor against the development of drug addiction in humans.

Polysomnographic Assessment of Sleep Comorbidities in Drug-Naïve Narcolepsy-Spectrum Disorders--A Japanese Cross-Sectional Study.

This is a large cross-sectional study which aimed to investigate comorbidity rate, degree of sleep-related breathing disorder, polysomnigraphically diagnosible rapid eye movement sleep behavior disorder/rapid eye movement sleep without atonia and periodic limb movements during sleep in Japanese drug-naïve patients with narcolepsy-spectrum disorders. A total of 158 consecutive drug naïve patients with narcolepsy with cataplexy, 295 patients with narcolepsy without cataplexy and 395 patients with idiopathic hypersomnia without long sleep time were enrolled. From retrospectively analyzed data of nocturnal polysomnography and multiple sleep latency test, higher rates of periodic limb movements during sleep (> = 15 h(-1)) (10.2%) and polysomnographically diagnosable rapid eye movement sleep behavior disorder (1.9%) were found in patients with narcolepsy with cataplexy. They had more severe periodic limb movements during sleep especially during rapid eye movement sleep and higher percentages of rapid eye movement sleep without atonia than the other two patient groups. In the present large sample study, Japanese drug naïve patients with narcolepsy with cataplexy showed the highest comorbidity rates of periodic limb movements during sleep, polysomnographically diagnosable rapid eye movement sleep behavior disorder and rapid eye movement sleep without atonia among those with the other narcolepsy-spectrum disorders; the rates were lower than those for Western patients.

Car Crashes and Central Disorders of Hypersomnolence: A French Study.

BACKGROUND: Drowsiness compromises driving ability by reducing alertness and attentiveness, and delayed reaction times. Sleep-related car crashes account for a considerable proportion of accident at the wheel. Narcolepsy type 1 (NT1), narcolepsy type 2 (NT2) and idiopathic hypersomnia (IH) are rare central disorders of hypersomnolence, the most severe causes of sleepiness thus being potential dangerous conditions for both personal and public safety with increasing scientific, social, and political attention. Our main objective was to assess the frequency of recent car crashes in a large cohort of patients affected with well-defined central disorders of hypersomnolence versus subjects from the general population. METHODS: We performed a cross-sectional study in French reference centres for rare hypersomnia diseases and included 527 patients and 781 healthy subjects. All participants included needed to have a driving license, information available on potential accident events during the last 5 years, and on potential confounders; thus analyses were performed on 282 cases (71 IH, 82 NT2, 129 NT1) and 470 healthy subjects. RESULTS: Patients reported more frequently than healthy subjects the occurrence of recent car crashes (in the previous five years), a risk that was confirmed in both treated and untreated subjects at study inclusion (Untreated, OR = 2.21 95%CI = [1.30-3.76], Treated OR = 2.04 95%CI = [1.26-3.30]), as well as in all disease categories, and was modulated by subjective sleepiness level (Epworth scale and naps). Conversely, the risk of car accidents of patients treated for at least 5 years was not different to healthy subjects (OR = 1.23 95%CI = [0.56-2.69]). Main risk factors were analogous in patients and healthy subjects. CONCLUSION: Patients affected with central disorders of hypersomnolence had increased risk of recent car crashes compared to subjects from the general population, a finding potentially reversed by long-term treatment.

Cerebrospinal fluid hypocretin 1 deficiency, overweight, and metabolic dysregulation in patients with narcolepsy.

STUDY OBJECTIVES: The possible relationship between cerebrospinal fluid (CSF) hypocretin and leptin levels, overweight, and association to risk factors for diabetes 2 in narcolepsy with cataplexy were compared to patients with idiopathic hypersomnia and controls. PATIENTS: 26 patients with narcolepsy, cataplexy, and hypocretin deficiency; 23 patients with narcolepsy, cataplexy, and normal hypocretin values; 11 patients with idiopathic hypersomnia; and 43 controls. MEASUREMENTS AND RESULTS: Body mass index (BMI), serum leptin, and HbA1C were measured in patients and controls; and CSF hypocretin 1 and leptin measured in all patients. Female and male patients with narcolepsy and hypocretin deficiency had the highest mean BMI (27.8 and 26.2, respectively), not statistically different from patients with narcolepsy and normal hypocretin or controls, but statistically higher than the patients with idiopathic hypersomnia (p < 0.001 and 0.011, respectively). The number of obese patients (BMI > 30) was increased in both narcolepsy groups. Serum and CSF leptin levels correlated positively to BMI in patients and controls, but not to CSF hypocretin concentrations. HbA1C was within normal levels and similar in all groups. CONCLUSIONS: The study confirms a moderate tendency to obesity (BMI > 30) and overweight in patients with narcolepsy and cataplexy. Obesity was not correlated to hypocretin deficiency or reduced serum or CSF leptin concentrations. We suggest that overweight and possible metabolic changes previously reported in narcolepsy, may be caused by other mechanisms.

Benefit and risk of modafinil in idiopathic hypersomnia vs. narcolepsy with cataplexy.

BACKGROUND: The benefit/risk ratio of modafinil was recently re-evaluated by the European Medicines Agency and was shown to be negative for idiopathic hypersomnia (IH) because of insufficient data. OBJECTIVE: To evaluate the benefit/risk ratio of modafinil in idiopathic hypersomnia (with and without long sleep time) vs. narcolepsy/cataplexy. SUBJECTS AND METHODS: The benefit (Epworth sleepiness score, ESS; visual analog scale, patient and clinician opinions) and risks (habituation, adverse effects) of modafinil were studied in a consecutive clinical cohort of 104 IH patients (59 with long sleep time) and 126 patients with narcolepsy/cataplexy. RESULTS: Modafinil was the first line treatment in 96-99% of patients. It produced a similar ESS change in IH patients and in narcolepsy patients (-2.6±5.1 vs. -3±5.1) and a similar benefit as estimated by the patients (6.9±2.7 vs. 6.5±2.5 on a visual analog scale) and clinicians. The ESS change was lower in IH patients with long sleep time than in those without. Sudden loss of efficacy and habituation were rare in both groups. Patients with IH reported similar but more frequent adverse effects with modafinil than narcolepsy patients: nervousness (14%), palpitations (13%), and headache (11%). CONCLUSION: Modafinil has an excellent benefit/risk ratio in idiopathic hypersomnia, with or without long sleep time, similar to its effect on narcolepsy/cataplexy.

Hypersomnia in children: interface with psychiatric disorders.

Patients being evaluated in child psychiatry clinics for behavior and mood disturbances frequently exhibit daytime sleepiness. Conversely, patients being evaluated for hypersomnia by sleep specialists may have depressed mood or hyperactive and aggressive behavior. The etiology of daytime sleepiness in children and adolescents is diverse and includes inadequate sleep hygiene, obstructive sleep apnea, delayed sleep phase syndrome, idiopathic hypersomnia, periodic hypersomnia, narcolepsy, and mood disorders per se. Treatment of a sleep disorder can have a favorable impact on alertness and quality of life. A high index of suspicion for sleep problems should be maintained in children and adolescents with psychiatric disorders.

Idiopathic hypersomnia with and without long sleep time: a controlled series of 75 patients.

OBJECTIVE: To characterize the clinical, psychological, and sleep pattern of idiopathic hypersomnia with and without long sleep time, and provide normative values for 24-hour polysomnography. SETTING: University Hospital. DESIGN: Controlled, prospective cohort. PARTICIPANTS: 75 consecutive patients (aged 34 +/- 12 y) with idiopathic hypersomnia and 30 healthy matched controls. INTERVENTION: Patients and controls underwent during 48 hours a face-to-face interview, questionnaires, human leukocyte antigen genotype, a night polysomnography and multiple sleep latency test (MSLT), followed by 24-h ad libitum sleep monitoring. RESULTS: Hypersomniacs had more fatigue, higher anxiety and depression scores, and more frequent hypnagogic hallucinations (24%), sleep paralysis (28%), sleep drunkenness (36%), and unrefreshing naps (46%) than controls. They were more frequently evening types. DQB1*0602 genotype was similarly found in hypersomniacs (24.2%) and controls (19.2%). Hypersomniacs had more frequent slow wave sleep after 06:00 than controls. During 24-h polysomnography, the 95% confidence interval for total sleep time was 493-558 min in controls, versus 672-718 min in hypersomniacs. There were 40 hypersomniacs with and 35 hypersomniacs without long ( > 600 min) sleep time. The hypersomniacs with long sleep time were younger (29 +/- 10 vs 40 +/- 13 y, P = 0.0002), slimmer (body mass index: 26 +/- 5 vs 23 +/- 4 kg/m2; P = 0.005), and had lower Horne-Ostberg scores and higher sleep efficiencies than those without long sleep time. MSLT latencies were normal (> 8 min) in 71% hypersomniacs with long sleep time. CONCLUSIONS: Hypersomnia, especially with long sleep time, is frequently associated with evening chronotype and young age. It is inadequately diagnosed using MSLT.

Psychological health in central hypersomnias: the French Harmony study.

BACKGROUND: A large observational French study of central hypersomnia, including narcolepsy with cataplexy (C+), without cataplexy (C-) and idiopathic hypersomnia (IH), was conducted to clarify the relationships between the severity of the condition, psychological health and treatment response. METHODS: 601 consecutive patients over 15 years of age suffering from central hypersomnia were recruited on excessive daytime sleepiness, polysomnography and Multiple Sleep Latency Test (MSLT) results. 517 (47.6% men, 52.4% women) were finally included: 82.0% C+, 13.2% C- and 4.8% IH. Face to face standardised clinical interviews plus questionnaires (Epworth Sleepiness Scale (ESS), short version Beck Depression Inventory (S-BDI), Pittsburgh Sleep Quality Index (PSQI) and 36-item Short Form Health Survey (SF-36)) were performed. Patients affected with a different diagnosis and with and without depressive symptoms were compared. RESULTS: Mean ESS and body mass index were higher in C+ compared with C-/IH patients. Half of the patients (44.9%) had no depressive symptoms while 26.3% had mild, 23.2% moderate and 5.6% severe depressive symptoms. C+ patients had higher S-BDI and PSQI and lower SF-36 scores than C-/IH patients. Depressed patients had higher ESS scores than non-depressed patients, with no difference in age, gender, duration of disease or MSLT parameters. Finally, C+ patients treated with anticataplectic drugs (38.7%) had higher S-BDI and lower SF-36 scores than C+ patients treated with stimulants alone. CONCLUSION: Our data confirmed the high frequency of depressive symptoms and the major impact of central hypersomnias on health related quality of life, especially in patients with cataplexy. We recommend a more thorough assessment of mood impairment in central hypersomnias, especially in narcolepsy-cataplexy.

Idiopathic hypersomnia: a study of 77 cases.

STUDY OBJECTIVES: To review the clinical and polysomnographic characteristics of idiopathic hypersomnia as well as the long-term response to treatment. SETTING: The Respiratory Support and Sleep Centre at Papworth Hospital, Cambridge, UK. PATIENTS AND DESIGN: A large database of more than 6000 patients with sleep disorders was reviewed. A retrospective study of the clinical and polysomnographic characteristics of 77 patients with idiopathic hypersomnia was performed. Comparison with a similar group of patients with narcolepsy was performed. The response to drug treatment was assessed in 61 patients over a mean follow-up of 3.8 years. MEASUREMENTS AND RESULTS: Idiopathic hypersomnia was 60% as prevalent as narcolepsy. Comparison with a similar group of patients with narcolepsy showed that those with idiopathic hypersomnia were more likely to have prolonged unrefreshing daytime naps, a positive family history, increased slow-wave sleep, and a longer sleep latency on the Multiple Sleep Latency Test. The results of the Multiple Sleep Latency Test were not helpful in predicting disease severity or treatment response. The clinical features were heterogeneous and of variable severity. The majority of patients with idiopathic hypersomnia had symptoms that remained stable over many years, but 11% had spontaneous remission, which was never seen in narcolepsy. Two thirds of patients with idiopathic hypersomnolence had a sustained improvement in daytime somnolence with medication, although a third needed high doses or combinations of drugs. CONCLUSIONS: Idiopathic hypersomnolence has characteristic clinical and polysomnographic features but the prolonged latency on the Multiple Sleep Latency Test raises doubt about the validity of this test within the current diagnostic criteria. The disease often responds well to treatment and a substantial minority of patients appear to spontaneously improve.