Atypical isolated cataplexy: two case reports and a mini-review

Cataplexy is the sudden loss of muscle tone often provoked by emotion such as laughter or excitement. Cataplexy is one of the essential diagnostic features of Narcolepsy type 1 (NT1). We describe two cases of isolated cataplexy with different outcomes, highlighting the diagnostic and prognostic challenges. There is conflicting literature as to whether it is a legitimate standalone diagnosis or an early warning sign of narcolepsy. Our cases do not fit with current diagnostic criteria for narcolepsy, yet still share some clinical or laboratory features. These ambiguous cases question what the mechanistic relationship between narcolepsy and cataplexy may be.

Rapid eye movement sleep is initiated by basolateral amygdala dopamine signaling in mice

The sleep cycle is characterized by alternating non-rapid eye movement (NREM) and rapid eye movement (REM) sleeps. The mechanisms by which this cycle is generated are incompletely understood. We found that a transient increase of dopamine (DA) in the basolateral amygdala (BLA) during NREM sleep terminates NREM sleep and initiates REM sleep. DA acts on dopamine receptor D2 (Drd2)-expressing neurons in the BLA to induce the NREM-to-REM transition. This mechanism also plays a role in cataplectic attacks-a pathological intrusion of REM sleep into wakefulness-in narcoleptics. These results show a critical role of DA signaling in the BLA in initiating REM sleep and provide a neuronal basis for sleep cycle generation.

A five-year longitudinal study reveals progressive cortical thinning in narcolepsy and faster cortical thinning in relation to early-onset

Narcolepsy with cataplexy is characterized by excessive daytime sleepiness, cataplexy, and other REM sleep phenomena. Previous MRI studies were cross-sectional in design and could not adequately address if disease progression leads the brain structural abnormalities in narcolepsy. Our analysis in patients using longitudinally collected brain MRIs (n = 17; 2 scans per patient; scan interval: 4.7 ± 1.9 years) revealed widespread progressive cortical thinning in bilateral dorsolateral frontal and fusiform cortices, right anterior cingulate (corrected p < 0.05). Cross-sectional analyses showed faster progressive cortical thinning in patients than controls (n = 83, one scan per subject available), which we confirmed significant in the analysis of a small-set of longitudinal control data (n = 10). The pattern of progressive thinning in patients was overlapped well with those found in structural and functional studies of narcolepsy. We also found a faster progression of cortical thinning and worse disease severity (decreased sleep efficiency, increased sleep latency and arousal index) over time in a subgroup of patients with earlier disease onset (n = 9, onset age: 15.9 ± 2.5 years old) compared to later disease onset (n = 8, 25.3 ± 4.9). The faster progressive cortical thinning and worse disease severity over time in the patients with early-onset suggest compelling evidence of disease progression existing in this phenotype of narcolepsy syndrome. Our result based on a small dataset, however, demands a more careful investigation of the underlying mechanism.

Late Diagnosis of Narcolepsy With Cataplexy: A Novel Case of Cataplectic Facies Presenting in an Elderly Woman

None

Cataplectic facies is an unusual feature described in children with narcolepsy and cataplexy. The typical manifestations of cataplectic facies consist of repetitive mouth opening, tongue protrusion, and ptosis. An interesting observation is that the usual emotional triggers associated with cataplexy such as laughter and joking are not always present, thus hampering diagnosis of the underlying syndrome. Cataplectic facies is thought to be a phenomenon observed in the early stages of narcolepsy type 1 and is thought to disappear by the time the patient reaches puberty. We present a unique case of an elderly woman with narcolepsy type 1 demonstrating cataplectic facies. The novel circumstances of this case highlight that facial cataplexy can present later in life, in contrast with previous descriptions that report resolution of cataplectic facies before puberty. Wider recognition of these features throughout the life course may aid in accurate diagnosis and thereby ensure swift access to appropriate treatment.

Status Cataplecticus Following Abrupt Withdrawal of Clomipramine

Presentation This is a case of a 31 year old gentleman who suffered an attack of status cataplecticus following abrupt withdrawal of clomipramine. Diagnosis Clomipramine was temporarily discontinued in order to confirm a suspected diagnosis of narcolepsy using Multiple Sleep Latency Testing. This precipitated an episode of status cataplecticus which resolved with re-introduction of therapy. A diagnosis of narcolepsy was later confirmed with undetectable levels of hypocretin/orexin in the CSF. Treatment Re-introduction of clomipramine led to resolution of status cataplecticus. The patient now remains stable with regards to his cataplexy on clomipramine 30mg. Discussion There have been a total of 4 case reports of status cataplecticus following withdrawal of antidepressant therapy. In all cases, reintroduction of anti-cataplectic therapy led to resolution of attacks. The abrupt discontinuation of an SSRI is believed to precipitate cataplexy attacks due to reduction in noradrenergic tone.

Narcolepsy and emotional experience: a review of the literature

Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations, and sleep paralysis. This disease affects significantly the overall patient functioning, interfering with social, work, and affective life. Some symptoms of narcolepsy depend on emotional stimuli; for instance, cataplectic attacks can be triggered by emotional inputs such as laughing, joking, a pleasant surprise, and also anger. Neurophysiological and neurochemical findings suggest the involvement of emotional brain circuits in the physiopathology of cataplexy, which seems to depending on the dysfunctional interplay between the hypothalamus and the amygdala associated with an alteration of hypocretin levels. Furthermore, behavioral studies suggest an impairment of emotions processing in narcolepsy-cataplexy (NC), like a probable coping strategy to avoid or reduce the frequency of cataplexy attacks. Consistently, NC patients seem to use coping strategies even during their sleep, avoiding unpleasant mental sleep activity through lucid dreaming. Interestingly, NC patients, even during sleep, have a different emotional experience than healthy subjects, with more vivid, bizarre, and frightening dreams. Notwithstanding this evidence, the relationship between emotion and narcolepsy is poorly investigated. This review aims to provide a synthesis of behavioral, neurophysiological, and neurochemical evidence to discuss the complex relationship between NC and emotional experience and to direct future research.

Rewiring brain circuits to block cataplexy in murine models of narcolepsy

Narcolepsy was first identified almost 130 years ago, but it was only 15 years ago that it was identified as a neurodegenerative disease linked to a loss of orexin neurons in the brain. It is unclear what causes the orexin neurons to die, but our strategy has been to place the gene for orexin into surrogate neurons in the validated mouse models of narcolepsy, and test whether it can block narcolepsy symptoms, such as cataplexy. In both the orexin knockout and the orexin-ataxin-3 mouse models of narcolepsy we have found that cataplexy can be blocked if the surrogate neurons are part of the circuit responsible for cataplexy. We have also determined that the orexin gene can be inserted into surrogate neurons in the amygdala to block emotion-induced cataplexy. Through the use of optogenetics we anticipate that it will be possible to preemptively block cataplexy.

The Roles of Dopamine and Hypocretin in Reward: A Electroencephalographic Study

The proper functioning of the mesolimbic reward system is largely dependent on the neurotransmitter dopamine. Recent evidence suggests that the hypocretin system has significant projections to this reward system. We examined the distinct effects of reduced dopamine or reduced hypocretin levels on reward activity in patients with Parkinson’s disease, dopamine deficient, as well as patients with narcolepsy-cataplexy, hypocretin depleted, and healthy controls. Participants performed a simple game-like task while high-density electroencephalography was recorded. Topography and timing of event-related potentials for both reward cue, and reward feedback was examined across the entire dataset. While response to reward cue was similar in all groups, two distinct time points were found to distinguish patients and controls for reward feedback. Around 160ms both patient groups had reduced ERP amplitude compared to controls. Later at 250ms, both patient groups also showed a clear event-related potential (ERP), which was absent in controls. The initial differences show that both patient groups show a similar, blunted response to reward delivery. The second potential corresponds to the classic feedback-related negativity (FRN) potential which relies on dopamine activity and reflects reward prediction-error signaling. In particular the mismatch between predicted reward and reward subsequently received was significantly higher in PD compared to NC, independent of reward magnitude and valence. The intermediate FRN response in NC highlights the contribution of hypocretin in reward processing, yet also shows that this is not as detrimental to the reward system as in Parkinson’s. Furthermore, the inability to generate accurate predictions in NC may explain why hypocretin deficiency mediates cataplexy triggered by both positive and negative emotions.

Histamine Transmission Modulates the Phenotype of Murine Narcolepsy Caused by Orexin Neuron Deficiency

Narcolepsy type 1 is associated with loss of orexin neurons, sleep-wake derangements, cataplexy, and a wide spectrum of alterations in other physiological functions, including energy balance, cardiovascular, and respiratory control. It is unclear which narcolepsy signs are directly related to the lack of orexin neurons or are instead modulated by dysfunction of other neurotransmitter systems physiologically controlled by orexin neurons, such as the histamine system. To address this question, we tested whether some of narcolepsy signs would be detected in mice lacking histamine signaling (HDC-KO). Moreover, we studied double-mutant mice lacking both histamine signaling and orexin neurons (DM) to evaluate whether the absence of histamine signaling would modulate narcolepsy symptoms produced by orexin deficiency. Mice were instrumented with electrodes for recording the electroencephalogram and electromyogram and a telemetric arterial pressure transducer. Sleep attacks fragmenting wakefulness, cataplexy, excess rapid-eye-movement sleep (R) during the activity period, and enhanced increase of arterial pressure during R, which are hallmarks of narcolepsy in mice, did not occur in HDC-KO, whereas they were observed in DM mice. Thus, these narcolepsy signs are neither caused nor abrogated by the absence of histamine. Conversely, the lack of histamine produced obesity in HDC-KO and to a greater extent also in DM. Moreover, the regularity of breath duration during R was significantly increased in either HDC-KO or DM relative to that in congenic wild-type mice. Defects of histamine transmission may thus modulate the metabolic and respiratory phenotype of murine narcolepsy.

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.

Sleep physiology: setting the right tone

Humans prone to cataplexy experience sudden losses of postural muscle tone without a corresponding loss of conscious awareness. The brain mechanisms underlying this debilitating decoupling are now better understood, thanks to a new study using cataplectic mice.

Non-dipping blood pressure profile in narcolepsy with cataplexy

BACKGROUND

Patients with narcolepsy-cataplexy (NC) mostly exhibit undetectable hypocretin levels. Hypocretin system is one of the key players in the complex interaction between sleep and the cardiovascular system. We tested the hypothesis that hypocretin deficiency affects cardiovascular risk factors by measuring nighttime and daytime ambulatory blood pressure (BP) and the night-to-day BP ratio as well as endothelial dysfunction by the digital pulse amplitude response in drug-free patients with NC compared to controls.

METHODOLOGY

Sleep, clinical and biological cardiovascular risk factors, fingertip peripheral arterial tonometry, and 24-hour ambulatory BP monitoring were recorded in 50 drug-free patients with NC and 42 healthy control subjects, except for BP monitoring available in all controls but in 36 patients with NC.

PRINCIPAL FINDINGS

More patients than controls were smokers, obese and with dyslipidemia. One-third of patients with NC were "non-dippers" (defined as <10% drop in BP during sleep) compared to only 3% of controls. The diastolic non-dipper BP profile had up to 12-fold higher odds of being associated with NC. We noted negative correlations between mean diastolic BP fall during night, REM sleep percentage and number of sleep onset REM periods, and a positive correlation with mean sleep latency on the MSLT. The digital pulse amplitude response measured by fingertip was similar between NC and controls.

CONCLUSION

We found a high percentage of non-dippers in patients with NC with association with REM sleep dysregulation. The blunted sleep-related BP dip in NC may be of clinical relevance, as it may indicate increased risk for cardiovascular events.

Hypocretin and its emerging role as a target for treatment of sleep disorders

The neuropeptides hypocretin-1 and -2 (orexin A and B) are critical in the regulation of arousal and maintenance of wakefulness. Understanding the role of the hypocretin system in sleep/wake regulation has come from narcolepsy-cataplexy research. Deficiency of hypocretin results in loss of sleep/wake control with consequent unstable transitions from wakefulness into non-rapid eye movement (REM) and REM sleep, and clinical manifestations including daytime hypersomnolence, sleep attacks, and cataplexy. The hypocretin system regulates sleep/wake control through complex interactions between monoaminergic/cholinergic wake-promoting and GABAergic sleep-promoting neuronal systems. Research for the hypocretin agonist and the hypocretin antagonist for the treatment of sleep disorders has vigorously increased over the past 10 years. This review will focus on the origin, functions, and mechanisms in which the hypocretin system regulates sleep and wakefulness, and discuss its emerging role as a target for the treatment of sleep disorders.

Narcolepsy in adolescents

Narcolepsy is a disorder of children and adolescence, but until recently it was often not identified until adulthood, with a reported time from onset to diagnosis of about a decade. This disorder affects approximately 0.05% of the population and starts in childhood and adolescence about half of the time. With narcolepsy, the boundaries between wake, sleep, and dreams are blurred. The cardinal features of narcolepsy-cataplexy are daytime somnolence, cataplexy (sometimes occurring long after onset of sleepiness), sleep paralysis, and hypnagogic hallucinations. Weight gain, disturbed nocturnal sleep, and social/school functional changes are common; reactive substance use to maintain wakefulness during the day may also be seen. Males and females are equally affected. It is classically associated with HLA DQB1*0602, the most specific genetic marker for narcolepsy across all ethnic groups. CSF hypocretin has recently been found to be depleted in this disorder, and late-breaking data support that the disease is caused by autoimmune destruction of hypocretin-producing neurons in the hypothalamus. There is no known cure for narcolepsy. Therapies include behavioral/ scheduling modification, medications to combat daytime sleepiness and cataplexy, and treatment of concomitant disorders leading to daytime sleepiness. The differential diagnosis for this disorder should include other disorders of excessive daytime sleepiness with a proclivity toward onset in adolescence, such as delayed sleep phase syndrome, obstructive sleep apnea, and insufficient sleep time; substance use; and less commonly neurologic disorders such as Klein Levin syndrome, Prader-Willi syndrome, and others. Immunomodulator therapy and hypocretin replacement are proposed therapies that hold promise for the future.

Dopaminergic regulation of sleep and cataplexy in a murine model of narcolepsy

STUDY OBJECTIVES

To determine if the dopaminergic system modulates cataplexy, sleep attacks and sleep-wake behavior in narcoleptic mice.

DESIGN

Hypocretin/orexin knockout (i.e., narcoleptic) and wild-type mice were administered amphetamine and specific dopamine receptor modulators to determine their effects on sleep, cataplexy and sleep attacks.

PATIENTS OR PARTICIPANTS

Hypocretin knockout (n = 17) and wild-type mice (n = 21).

INTERVENTIONS

Cataplexy, sleep attacks and sleep-wake behavior were identified using electroencephalogram, electromyogram and videography. These behaviors were monitored for 4 hours after an i.p. injection of saline, amphetamine and specific dopamine receptor modulators (D1- and D2-like receptor modulators).

MEASUREMENTS AND RESULTS

Amphetamine (2 mg/kg), which increases brain dopamine levels, decreased sleep attacks and cataplexy by 61% and 67%, suggesting that dopamine transmission modulates such behaviors. Dopamine receptor modulation also had powerful effects on sleep attacks and cataplexy. Activation (SKF 38393; 20 mg/kg) and blockade (SCH 23390; 1 mg/kg) of D1-like receptors decreased and increased sleep attacks by 77% and 88%, without affecting cataplexy. Pharmacological activation of D2-like receptors (quinpirole; 0.5 mg/kg) increased cataplectic attacks by 172% and blockade of these receptors (eticlopride; 1 mg/kg) potently suppressed them by 97%. Manipulation of D2-like receptors did not affect sleep attacks.

CONCLUSIONS

We show that the dopaminergic system plays a role in regulating both cataplexy and sleep attacks in narcoleptic mice. We found that cataplexy is modulated by a D2-like receptor mechanism, whereas dopamine modulates sleep attacks by a D1-like receptor mechanism. These results support a role for the dopamine system in regulating sleep attacks and cataplexy in a murine model of narcolepsy.

A case of narcolepsy with strictly unilateral cataplexy

I report a case of a 50-year-old African American woman who presented for a sleep medicine evaluation complaining of excessive daytime sleepiness of greater than 10 years' duration. She reported falling asleep while driving, talking with friends, and eating. Her Epworth Sleepiness Scale score was 21/24. Her history was positive for the presence of sleep paralysis. She denied visual or auditory hallucinations in the peri-sleep period.

Obesity accompanies narcolepsy with cataplexy but not narcolepsy without cataplexy

BACKGROUND

Narcolepsy with cataplexy (NC) differs from narcolepsy without cataplexy (NwoC) in the cerebrospinal fluid levels of hypocretin. Since hypocretin is known to regulate not only wakefulness but also eating behaviour, we decided to compare the two entities for body mass index (BMI) and the presence of obesity.

METHODS

Clinical data on patients with NC and NwoC was studied and examined, including nocturnal polysomnography and the Multiple Sleep Latency Test (MSLT). The results were rated against a group of age- and sex-matched healthy controls.

RESULTS

The BMI in NC (29.1±SD=5.8) was significantly higher than in NwoC (25.4±4.4) or in the controls (25.8±3.9) (p<0.001, F=17.4, df= 323), while no difference in BMI was found between NwoC and the controls. The proportion of patients with BMI >30 was significantly greater in NC (39.0%) than in NwoC (13.8%) or than in the control group (13.0%). A negative correlation of BMI and sleep latency in MSLT (p=0.009) was found in the combined NC and NwoC groups.

CONCLUSION

Unlike NC, NwoC has neither a higher BMI nor a higher incidence of obesity than the general population.

Falls, faints, fits and funny turns

In this practically oriented review, we will outline the clinical approach of patients with falls due to an impairment or loss of consciousness. Following a set of definitions, we describe the salient clinical features of disorders leading to such falls. Among falls caused by true loss of consciousness, we separate the clinical characteristics of syncopal falls (due to reflex syncope, hypovolemia, orthostatic hypotension or cardiac syncope) from falls due to other causes of transient unconsciousness, such as seizures. With respect to falls caused by an apparent loss of consciousness, we discuss the presentation of cataplexy, drop attacks, and psychogenic falls. Particular emphasis will be laid upon crucial features obtained by history taking for distinguishing between the various conditions that cause or mimic a transient loss of consciousness.

Childhood narcolepsy with partial facial cataplexy: a diagnostic dilemma

Sixteen percent of adults ultimately diagnosed with having narcolepsy/cataplexy experienced symptoms before the age of ten years, 4.5% even before the age of five years. The symptomatology in childhood narcolepsy/cataplexy can differ significantly from adults and can lead to misinterpretations and misdiagnosis. Standard diagnostic tools (polysomnography and multiple sleep latency test) can give false negative results and do not exclude the disorder. The decision to determine hypocretins in cerebrospinal fluid (CSF) should be made as early as possible in children. Here, we present a case of a five-year-old girl with acute onset of narcolepsy/cataplexy after a closed head trauma. The first symptoms were excessive daytime sleepiness, partial facial cataplexy and a serious behavioral disorder. Hypocretin-1 level (Hrt-1) in CSF was undetectable.

A consensus definition of cataplexy in mouse models of narcolepsy

People with narcolepsy often have episodes of cataplexy, brief periods of muscle weakness triggered by strong emotions. Many researchers are now studying mouse models of narcolepsy, but definitions of cataplexy-like behavior in mice differ across labs. To establish a common language, the International Working Group on Rodent Models of Narcolepsy reviewed the literature on cataplexy in people with narcolepsy and in dog and mouse models of narcolepsy and then developed a consensus definition of murine cataplexy. The group concluded that murine cataplexy is an abrupt episode of nuchal atonia lasting at least 10 seconds. In addition, theta activity dominates the EEG during the episode, and video recordings document immobility. To distinguish a cataplexy episode from REM sleep after a brief awakening, at least 40 seconds of wakefulness must precede the episode. Bouts of cataplexy fitting this definition are common in mice with disrupted orexin/hypocretin signaling, but these events almost never occur in wild type mice. It remains unclear whether murine cataplexy is triggered by strong emotions or whether mice remain conscious during the episodes as in people with narcolepsy. This working definition provides helpful insights into murine cataplexy and should allow objective and accurate comparisons of cataplexy in future studies using mouse models of narcolepsy.