Monoamine interactions in narcolepsy and hypersomnia: a preliminary report

Cerebrospinal fluid monoamine levels in central disorders of hypersomnolence

STUDY OBJECTIVES

Whether the cause of daytime sleepiness in narcolepsy type 1 (NT1) is a direct consequence of the loss of orexin (ORX) neurons or whether low orexin reduces the efficacy of the monoaminergic systems to promote wakefulness is unclear. The neurobiology underlying sleepiness in other central hypersomnolence disorders, narcolepsy type 2 (NT2), and idiopathic hypersomnia (IH), is currently unknown.

METHODS

Eleven biogenic amines including the monoaminergic neurotransmitters and their metabolites and five trace amines were measured in the cerebrospinal fluid (CSF) of 94 drug-free subjects evaluated at the French National Reference Center for Narcolepsy: 39 NT1(orexin-deficient) patients, 31 patients with objective sleepiness non orexin-deficient (NT2 and IH), and 24 patients without objective sleepiness.

RESULTS

Three trace amines were undetectable in the sample: tryptamine, octopamine, and 3-iodothyronamine. No significant differences were found among the three groups for quantified monoamines and their metabolites in crude and adjusted models; however, CSF 5-hydroxyindoleacetic acid (5-HIAA) levels tended to increase in NT1 compared to other patients after adjustment. Most of the biomarkers were not associated with ORX-A levels, clinical or neurophysiological parameters, but a few biomarkers (e.g. 3-methoxy-4-hydroxyphenylglycol and norepinephrine) correlated with daytime sleepiness and high rapid eye movement (REM) sleep propensity.

CONCLUSIONS

We found no striking differences among CSF monoamines, their metabolites and trace amine levels, and few associations between them and key clinical or neurophysiological parameters in NT1, NT2/IH, and patients without objective sleepiness. Although mostly negative, these findings are a significant contribution to our understanding of the neurobiology of hypersomnolence in these disorders that remain mysterious and deserve further exploration.

Update on hypersomnias of central origin

PURPOSE OF REVIEW

To describe the multiple clinical aspects of hypersomnias of central origin. Emphasis is given to the new pathophysiological pathways and treatment options described in the current literature.

RECENT FINDINGS

Narcolepsy is the most recognized of the hypersomnias of central origin. Hypocretin deficiency appears to underlie narcolepsy with cataplexy, and infections and vaccinations have been associated with disease onset. Targeted therapeutic approaches are currently underway. A putative naturally occurring constituent in the cerebrospinal fluid of patients with non-narcoleptic primary hypersomnias, able to stimulate γ-aminobutyric acid alpha receptors and induce sleep, has recently been postulated. Neuroimaging has also provided more insight into the pathophysiology of Kleine-Levin syndrome. Sleep deprivation is currently recognized as a major differential diagnosis.

SUMMARY

Excessive daytime sleepiness is the cardinal symptom of the hypersomnias of central origin, with major impact on the quality of life. It is important that clinicians be able to recognize these conditions, so that appropriate management or onward referral is expedited.

Successful treatment with levothyroxine for idiopathic hypersomnia patients with subclinical hypothyroidism

OBJECTIVE

Our objective was to discuss the effect of levothyroxine on excessive daytime sleepiness (EDS) and a prolonged nocturnal sleep at patients with idiopathic hypersomnia who presented with subclinical hypothyroidism.

METHODS

We present two patients with hypersomnia who complained of EDS and a prolonged nocturnal sleep time. Sleep architecture and subjective daytime sleepiness were estimated by polysomnography (PSG) and Epworth Sleepiness Scale (ESS), respectively. Diagnoses were made using the International Classification of Sleep Disorders, 2nd Edition criteria for idiopathic hypersomnia with long sleep time.

RESULTS

PSG demonstrated a short sleep latency, a prolonged total sleep time and normal proportions of all non-rapid eye movement (REM) and REM sleep stages. Nocturnal PSG excluded other causes of EDS. No medical, neurological and mental disorders were present. Their laboratory data indicated mildly elevated thyrotropin, despite free thyroxine (T4) and triiodothyronine (T3) estimates within their reference ranges, which is a characteristic of latent hypothyroidism. Levothyroxine (25 microg/day) was administrated orally. After treatment with levothyroxine for 8 weeks, the mean daily sleep times decreased. EDS was also improved, and a significant decrease in the ESS score was observed. Levothyroxine was effective for their hypersomnia and well tolerated.

CONCLUSIONS

It should be noted that hypersomnia may be associated with subclinical hypothyroidism, although few abnormalities in physical and neurological examinations are present.

Excessive daytime sleepiness: considerations for the psychiatrist

Excessive daytime sleepiness or pathologic sleepiness is a complaint found in patients who experience somnolence at unwanted times and adversely affects their daytime function. Although psychiatric illness, chronic medical illness, or medication side effects may be causes for fatigue, insufficient sleep is the most common cause of excessive daytime sleepiness in the general population. When an individual complains of frank sleepiness, in addition to insufficient sleep, important considerations in these patients are disturbances in the normal homeostatic mechanisms that govern sleep and wakefulness. This article summarizes the clinical presentation, the differential diagnosis, commonly used diagnostic tools, and treatment options for patients complaining of excessive daytime sleepiness.

Conditions of Primary Excessive Daytime Sleepiness

Excessive daytime somnolence is a prevalent problem in medical practice and in society. It exacts a great toll in quality of life, personal and public safety, and productivity. The causes of EDS are myriad, and careful evaluation is needed to determine the cause in each case. Although much progress has been made in discovering the pathophysiology of narcolepsy, much more remains to be understood, and far less is known about other primary conditions of EDS. Several methods have been developed to assess EDS, although each of them has limitations. Treatment is available for the great majority of cases.

Idiopathic Hypersomnia

In contrast to narcolepsy and the Kleine-Levin syndrome, idiopathic hypersomnia is a recently described sleep disorder. Absence of associated clinical features such as cataplexy or megaphagia and characteristic polysomnographic features such as sleep-onset REM episodes render positive diagnosis more uncertain in idiopathic hypersomnia than in the fwo former conditions. Consequently there has been an unfortunate tendency to label all difficult to classify cases of excessive daytime sleepiness as idiopathic hypersomnia. At present due to the description of new disorders such as upper airway resistance syndrome, narcolepsy without cataplexy, delayed sleep phase syndrome, all of which were formerly confused with idiopathic hypersomnia and the clear identification of a "polysymptomatic" or "classic" form of idiopathic hypersomnia, the limits of the disorder become more precise. Still there are a number of cases of isolated excessive daytime sleepiness with no prolonged night sleep, no difficulty waking up, which lay between narcolepsy and genuine idiopathic hypersomnia. Thus there is a definite need to further develop laboratory investigations to help identify and classify these cases. Moreover pathophysiology and pathogenesis are still in their infancy and efforts have to be pursued in this direction. Treatment has not made consistent progress except for the use of a new wake promoting compound, modafinil, which has not yet been evaluated in controlled studies.

Idiopathic hypersomnia

Identification of idiopathic hypersomnia dates back 20 years only. It typically consists of prolonged nocturnal sleep, great difficulty waking up in the morning or at the end of a nap, and constant or recurrent excessive daytime sleepiness. Complete and incomplete forms are encountered. Twenty-three subjects fulfilling ICSD criteria are reported with clinical, polysomnographic and immunogenetic data. Considering differential diagnosis is an important step in the diagnosis of idiopathic hypersomnia. Idiopathic hypersomnia is much less frequent than narcolepsy. A strong genetic component is suggested by the high proportion of familial cases. No association with HLA has been evidenced to date.

Idiopathic hypersomnia

Idiopathic hypersomnia is not as well delineated as narcolepsy and its history is much more recent. There are at least two forms of the disorder: (1) a polysymptomatic form, characterized by excessive daytime sleepiness, nocturnal sleep of abnormally long duration, and signs of sleep drunkenness on awakening, and (2) a monosymptomatic form that manifests only by excessive daytime sleepiness. The most widely used laboratory procedures are nocturnal polysomnographic recording following by an MSLT demonstrating a mean sleep latency of less than 10 minutes. At least in the polysymptomatic form, however, continuous polysomnography on an ad lib protocol deserves to be performed to catch the abnormally long major sleep episode and the long unrefreshing naps. Idiopathic hypersomnia is probably one of the most overdiagnosed sleep disorders. Several other disorders must be excluded before the diagnosis can be considered conclusive. Treatment of idiopathic hypersomnia relies on stimulants, which are frequently less effective and less well tolerated than in narcolepsy.

Compound narcolepsy: sleep pattern and involution

A review of studies of sleep in three-month-old infants, narcoleptics, and normal adults indicates that the sleep pattern in compound narcolepsy is in many ways involuted. Similarities in sleep onsets, REM-specific movement, REM dissociation, ambiguous sleep, nocturnal arousals, diurnal sleep-wake cycles, and relatively limited quiet-awake time are discussed as part of a global inability to inhibit state changes common to both infants and compound narcoleptics. The analogy with infant sleep patterns and results of studies of brain function in narcoleptics suggest that forebrain inhibitory processes are more important in narcoleptic symptomology than is brainstem dysfunction. Puberty and old age are critical periods for the development or exacerbation of the involuted sleep pattern. Closer study of the early development of narcoleptics and of lability of state changes in narcolepsy may aid in diagnosis and prognosis for susceptible individuals.

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.