Narcolepsy and other disorders of excessive sleepiness

Analysis of cortical thickness in narcolepsy patients with cataplexy

STUDY OBJECTIVES

To investigate differences in cortical thickness in narcolepsy patients with cataplexy and control subjects.

DESIGN

Cortical thickness was measured using a 3-D surface-based method that enables more accurate measurement in deep sulci and localized regional mapping.

SETTING

University hospital.

PATIENTS AND PARTICIPANTS

We enrolled 28 patients with narcolepsy and cataplexy and 33 age-and sex-matched control subjects.

INTERVENTIONS

Cortical thickness was measured using a direct method for calculating the distance between corresponding vertices from inner and outer cortical surfaces.

MEASUREMENTS AND RESULTS

We normalized cortical surfaces using 2-D surface registration and performed diffusion smoothing to reduce the variability of folding patterns and to increase the power of the statistical analysis. Localized cortical thinning in narcolepsy patients with cataplexy was found in orbitofrontal gyri, dorsolateral and medial prefrontal cortexes, insula, cingulate gyri, middle and inferior temporal gyri, and inferior parietal lobule of the right and left hemispheres at the level of a false discovery rate P<0.05. No significant local increases in cortical thickness were observed in narcolepsy patients. A significant negative correlation was observed between the narcolepsy patients' scores on the Epworth Sleepiness Scale and the cortical thickness of the left supramarginal gyrus.

CONCLUSIONS

Cortical thinning in narcolepsy patients with cataplexy in localized anatomic brain regions may serve as a possible neuroanatomic mechanism of the disturbances in attention, memory, emotion, and sleepiness.

Narcolepsy and other hypersomnias in children

PURPOSE OF REVIEW

We provide an update on the pathogenesis, diagnosis, assessment (clinical and laboratory), and treatment options for children with narcolepsy and other hypersomnias of central origin in order to raise awareness of these diseases and to highlight the clinical findings that should make the pediatrician suspect the diagnosis.

RECENT FINDINGS

Narcolepsy is a chronic rapid eye movement sleep disorder. Accumulating evidence indicates that signs of narcolepsy may start during childhood. Recent data suggest that a deficiency in the hypothalamic orexin/hypocretin system underlies the pathogenesis of narcolepsy with cataplexy. Confirmatory tests such as polysomnography, multiple sleep latency test, and actigraphy, along with referral to a sleep physician, maybe necessary in appropriate cases. Laboratory tests such as human leukocyte antigen typing and cerebrospinal fluid hypocretin-1 analysis are useful as adjuncts. Modafinil is now considered the first-line treatment for excessive sleepiness in adult patients with narcolepsy. Sodium oxybate is currently approved by the Food and Drug Administration for the treatment of narcolepsy with cataplexy in patients aged more than 16 years.

SUMMARY

Awareness of the extent of hypersomnia in children will allow physicians to effectively screen every child; once identified, further assessment should be performed in order to diagnose and treat the underlying cause. Better understanding of pathogenesis, availability of newer therapies with different mechanism of effect, and appropriately designed randomized clinical trials should allow improved management of children with narcolepsy.

Hypersomnia in Whipple disease: case report

Whipple disease (WD) is a rare systemic infection caused by Tropheryma whippelii. Neurological involvement has been recognised in 40% of patients, either as initial manifestations or during the course of the disease. We report on a 45 years-old man with WD with initial, persistent and irresistible episodes of daytime somnolence. The patient was HLA-DQB1*0602 positive (genetic marker for narcolepsy). WD diagnosis was suspected on clinical and MRI basis and confirmed by histological and immunohistochemical study of duodenal biopsy. Forty months later all clinical features improved, narcoleptic-like episodes disappeared and cerebral MRI and CSF normalised. Longitudinal neurophysiological studies revealed persistent sleep pattern abnormalities with sleep fragmentation, paucity of slow wave and of REM sleep. The disruption of the hypocretin circuitry in the hypothalamic - diencephalic region triggered by the infection was the probable cause of the hypersomnia and narcopleptic symptoms. WD should be added to the list of causes of secondary hypersomnia.

Cerebral perfusion abnormality in narcolepsy with cataplexy

To investigate abnormal cerebral perfusion in narcoleptics with cataplexy, 25 narcoleptics with cataplexy and 25 normal controls were enrolled in this study. Cerebral perfusion was measured by brain single photon emission computed tomography (SPECT) using 99mTc-ethylcysteinate dimer. Patients and normal controls had not received any medication prior to the SPECT scan. Differences in cerebral perfusion between narcoleptics and normal controls were subjected to statistical parametric mapping (SPM) analysis. Overnight polysomnography and multiple sleep latency test (MSLT) were performed in all patients. Brain SPECT was carried out on all patients and normal controls during the waking state. Clinical symptoms and MSLT results of all patients are in accord with the International Classification of Sleep Disorders criteria for narcolepsy. MSLT showed a short mean sleep latency (1.69 +/- 1.0 min) and 2-5 sleep onset REM periods in individual patient. SPM analysis of brain SPECT showed hypoperfusion of the bilateral anterior hypothalami, caudate nuclei, and pulvinar nuclei of thalami, parts of the dorsolateral/ventromedial prefrontal cortices, parahippocampal gyri, and cingulate gyri in narcoleptics [P < 0.05 by Student's t test with false discovery rate (FDR) correction]. Significant hypoperfusion in the white matter of frontal and parietal lobes was also noted in narcoleptics. This study shows reduced cerebral perfusion in subcortical structures and cortical areas in narcoleptics. The distribution of abnormal cerebral perfusion is concordant with the pathway of the cerebral hypocretin system and may explain the characteristic features of narcolepsy, i.e., cataplexy, emotional lability, and attention deficit.