CSF hypocretin levels in Guillain-Barre syndrome and other inflammatory neuropathies

Utility of the sleep stage sequence preceding sleep onset REM periods for the diagnosis of narcolepsy: a study in a Japanese cohort

BACKGROUND

The minimum narcolepsy criteria "mean sleep latency (MSL) ≤8 min and ≥2 sleep onset rapid eye movement (REM) periods (SOREMPs) on polysomnography (PSG) and the multiple sleep latency test (MSLT)," according to The International Classification of Sleep Disorders, Third Edition (ICSD-3), are not specific to narcolepsy. Recently, the characteristic sleep stage sequences preceding SOREMPs in narcolepsy have received attention, but their diagnostic utility remains unclear.

METHODS

We retrospectively reviewed PSG/MSLT records and chart data for 102 Japanese patients with hypersomnia and at least one SOREMP. We examined the sporadic rates of two sleep stage sequences preceding the SOREMPs-wakefulness or stage 1 to REM (W/S1→R) and stage 2 to REM (S2→R)-comparing these between patient groups with narcolepsy type 1 (N = 28), narcolepsy type 2 (N = 19), and other hypersomnia (N = 55). We also examined the utility of three simple indices using the occurrence of W/S1→R SOREMPs for distinguishing between narcolepsy and other hypersomnia in patients who satisfied the minimum narcolepsy criteria.

RESULTS

W/S1→R SOREMPs were significantly more frequent in narcolepsy than in other hypersomnia, and this tendency was also observed even in the patients who satisfied the minimum narcolepsy criteria. The three indices had moderate sensitivities and specificities for distinguishing between narcolepsy and other hypersomnia in patients satisfying the minimum narcolepsy criteria.

CONCLUSIONS

The W/S1→R pattern was observed significantly more frequently in narcolepsy than in other hypersomnia, suggesting it may help with differentiating narcolepsy from other hypersomnia in patients demonstrating the narcolepsy criteria, although its ability to do so may be modest.

Validation of the ICSD-2 criteria for CSF hypocretin-1 measurements in the diagnosis of narcolepsy in the Danish population

STUDY OBJECTIVES

The International Classification of Sleep Disorders (ICSD-2) criteria for low CSF hypocretin-1 levels (CSF hcrt-1) still need validation as a diagnostic tool for narcolepsy in different populations because inter-assay variability and different definitions of hypocretin deficiency complicate direct comparisons of study results.

DESIGN AND PARTICIPANTS

Interviews, polysomnography, multiple sleep latency test, HLA-typing, and CSF hcrt-1 measurements in Danish patients with narcolepsy with cataplexy (NC) and narcolepsy without cataplexy (NwC), CSF hcrt-1 measurements in other hypersomnias, neurological and normal controls. Comparisons of hypocretin deficiency and frequency of HLA-DQB1*0602-positivity in the Danish and eligible NC and NwC populations (included via MEDLINE search), by (re)calculation of study results using the ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean).

MEASUREMENTS AND RESULTS

In Danes, low CSF hcrt-1 was present in 40/46 NC, 3/14 NwC and 0/106 controls (P < 0.0001). Thirty-nine of 41 NC and 4/13 NwC patients were HLA-DQB1*0602-positive (P < 0.01). Hypocretin-deficient NC patients had higher frequency of cataplexy, shorter mean sleep latency, more sleep onset REM periods (P < 0.05) and more awakenings (NS) than did NC patients with normal CSF hcrt-1. Across populations, low CSF hcrt-1 and HLA-DQB1*0602-positivity characterized the majority of NC (80% to 100%, P = 0.53; 80% to 100%, P = 0.11) but a minority of NwC patients (11% to 29%, P = 0.75; 29% to 89%, P = 0.043).

CONCLUSION

The study provides evidence that hypocretin deficiency causes a more severe NC phenotype. The ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean) is valid for diagnosing NC, but not NwC. HLA-typing should precede CSF hcrt-1 measurements because hypocretin deficiency is rare in HLA-DQB1*0602-negative patients.

Contribution of central and peripheral factors to residual fatigue in Guillain–Barré syndrome

Many patients with Guillain-Barré syndrome (GBS) suffer from severe residual fatigue that has an uncertain basis. We determined the relative contribution of peripheral and central factors during a 2-min fatiguing sustained maximal voluntary contraction (MVC) in 10 neurologically well-recovered GBS patients and 12 age- and sex-matched healthy controls. Physiological fatigue was defined as the decline of voluntary force during an MVC of the biceps brachii. Relative amounts of peripheral fatigue and central activation failure were determined combining voluntary force and force responses to electrical stimulation. Surface electromyography was used to determine muscle-fiber conduction velocity. During the first minute of sustained MVC, peripheral fatigue developed more slowly in patients than in controls. Central fatigue only occurred in patients. The muscle-fiber conduction velocity was higher in patients. The initial MVC, decrease of MVC, initial force response, and initial central activation failure did not significantly differ between the groups. Although peripheral mechanisms cannot be excluded in the pathogenesis of residual fatigue after GBS, these results suggest that central changes are involved. This study thus provides further insight into the factors contributing to residual fatigue in GBS patients.

Hypocretins (orexins) and sleep–wake disorders

Since their discovery in 1998, the hypocretins (orexins)-peptides that are produced by a group of neurons situated in the posterolateral hypothalamus--have been shown to excite many CNS areas including many neuronal systems that regulate sleep and wakefulness. Animal studies indicate that hypocretins play a part in the regulation of various functions including arousal, muscle tone, locomotion, regulation of feeding behaviour, and neuroendocrine and autonomic functions. A link between hypocretin deficiency and narcoleptic symptoms was first shown in canine and rodent models of narcolepsy. Hypocretin deficiency, as shown by low or absent concentrations in CSF, was subsequently found in 90% of patients with sporadic narcolepsy-cataplexy, and less commonly in familial narcolepsy. In most other sleep-wake and neurological disorders, hypocretin concentrations are normal. Low concentrations were also found in hypothalamic disorders, acute traumatic brain injury, and a few other disorders. The exact function of the hypocretin system in sleep-wake regulation and its pathophysiological role in hypocretin-deficient and non-deficient narcolepsy as well as in non-narcoleptic, hypocretin-deficiency syndromes remain unclear.

Hypocretins (orexins): clinical impact of the discovery of a neurotransmitter

Hypothalamic excitatory hypocretin (orexin) neurons have been discovered in 1998 and found to have widespread projections to basal forebrain, monoaminergic and cholinergic brainstem, and spinal cord regions. The hypocretin system is influenced both neuronally (e.g. suprachiasmatic nucleus, GABAergic, cholinergic and aminergic brainstem nuclei) as well as metabolically (e.g. glucose, ghrelin, and leptin). Physiologically the hypocretin system has been implicated in the regulation of behaviours that are associated with wakefulness, locomotion, and feeding. A role in REM sleep, neuroendocrine, autonomic and metabolic functions has also been suggested. Pathophysiologically a deficient hypocretin neurotransmission has been found in human narcolepsy and (engineered) animal models of the disorder. Different mechanisms are involved including (1) degeneration of hypocretin neurons (mice), (2) hypocretin ligand deficiency (humans, mice, dogs), (3) hypocretin receptor deficiency (mice, dogs). Reports of low hypocretin-1 cerebrospinal fluid levels in neurologic conditions (e.g. Guillain-Barré syndrome, traumatic brain injury, hypothalamic lesions) with and without sleep-wake disturbances and, on the other hand, observations of normal levels in about 11% of narcoleptics raise questions about the exact nature and pathophysiological base of the link between hypocretin deficiency and clinical manifestations in human narcolepsy.

Symptomatic narcolepsy, cataplexy and hypersomnia, and their implications in the hypothalamic hypocretin/orexin system

Human narcolepsy is a chronic sleep disorder affecting 1:2000 individuals. The disease is characterized by excessive daytime sleepiness, cataplexy and other abnormal manifestations of REM sleep, such as sleep paralysis and hypnagogic hallucinations. Recently, it was discovered that the pathophysiology of (idiopathic) narcolepsy-cataplexy is linked to hypocretin ligand deficiency in the brain and cerebrospinal fluid (CSF), as well as the positivity of the human leukocyte antigen (HLA) DR2/DQ6 (DQB1*0602). The symptoms of narcolepsy can also occur during the course of other neurological conditions (i.e. symptomatic narcolepsy). We define symptomatic narcolepsy as those cases that meet the International Sleep Disorders Narcolepsy Criteria, and which are also associated with a significant underlying neurological disorder that accounts for excessive daytime sleepiness (EDS) and temporal associations. To date, we have counted 116 symptomatic cases of narcolepsy reported in literature. As, several authors previously reported, inherited disorders (n=38), tumors (n=33), and head trauma (n=19) are the three most frequent causes for symptomatic narcolepsy. Of the 116 cases, 10 are associated with multiple sclerosis, one case of acute disseminated encephalomyelitis, and relatively rare cases were reported with vascular disorders (n=6), encephalitis (n=4) and degeneration (n=1), and hererodegenerative disorder (three cases in a family). EDS without cataplexy or any REM sleep abnormalities is also often associated with these neurological conditions, and defined as symptomatic cases of EDS. Although it is difficult to rule out the comorbidity of idiopathic narcolepsy in some cases, review of the literature reveals numerous unquestionable cases of symptomatic narcolepsy. These include cases with HLA negative and/or late onset, and cases in which the occurrences of the narcoleptic symptoms are parallel with the rise and fall of the causative disease. A review of these cases (especially those with brain tumors), illustrates a clear picture that the hypothalamus is most often involved. Several cases of symptomatic cataplexy (without EDS) were also reported and in contrast, these cases appear to be often associated with non-hypothalamic structures. CSF hypocretin-1 measurement were also carried out in a limited number of symptomatic cases of narcolepsy/EDS, including narcolepsy/EDS associated with tumors (n=5), head trauma (n=3), vascular disorders (n=5), encephalopathies (n=3), degeneration (n=30), demyelinating disorder (n=7), genetic/congenital disorders (n=11) and others (n=2). Reduced CSF hypocretin-1 levels were seen in most symptomatic narcolepsy cases of EDS with various etiologies and EDS in these cases is sometimes reversible with an improvement of the causative neurological disorder and an improvement of the hypocretin status. It is also noted that some symptomatic EDS cases (with Parkinson diseases and the thalamic infarction) appeared, but they are not linked with hypocretin ligand deficiency. In contrast to idiopathic narcolepsy cases, an occurrence of cataplexy is not tightly associated with hypocretin ligand deficiency in symptomatic cases. Since CSF hypocretin measures are still experimental, cases with sleep abnormalities/cataplexy are habitually selected for CSF hypocretin measures. Therefore, it is still not known whether all or a large majority of cases with low CSF hypocretin-1 levels with CNS interventions, exhibit EDS/cataplexy. It appears that further studies of the involvement of the hypocretin system in symptomatic narcolepsy and EDS are helpful to understand the pathophysiological mechanisms for the occurrence of EDS and cataplexy.