Predominant cortical dysfunction in Guadeloupean parkinsonism.

Atypical parkinsonism is extremely frequent in Guadeloupe and may have an environmental cause. One-half of the patients with this tauopathy have dopa-resistant parkinsonism, tremor, subcortical dementia and abnormal eye movements suggestive of progressive supranuclear palsy (PSP). They also have hallucinations, dysautonomia, which are not characteristic of PSP. Furthermore, the oculomotor abnormalities and the tremor, which is jerky, differ from what is observed in classical PSP patients. We therefore undertook an electrophysiological study to characterize these features in greater detail. Nine representative Guadeloupean PSP-like (Gd-PSP) patients were selected for electro-oculographic recordings of horizontal eye movements [visually guided saccades (VGS), antisaccades (AS) and smooth pursuit], clinical evaluation of vertical saccade velocity and electrophysiological analysis of abnormal limb movements [electromyographic polygraphy, EEG jerk-locked-back-averaging (JLBA) and long-loop C-reflex]. Vertical saccade velocity was reduced in five patients. The velocity of horizontal VGS was normal, although the latencies were increased and horizontal smooth pursuit (HSP) was mostly saccadic. The AS error rate was above 70% in most patients. Myoclonus was detected in 89% of the Gd-PSP patients. It was mainly small amplitude rest and action myoclonus in the upper limbs, characterized by short arrhythmic 24-76 ms bursts and was of cortical origin, as confirmed by JLBA in five patients. In conclusion, Gd-PSP patients have cortical myoclonus and cortical oculomotor impairments, but only minor signs of brainstem oculomotor dysfunction, suggesting that cortical dysfunction predominates over brainstem impairments. This electrophysiological study, added to previous clinical, neuropsychological and neuroradiological studies, has enriched the characterization of Guadeloupean atypical parkinsonism, which thus appears to be a new clinical entity.

REM sleep behavior disorder in patients with guadeloupean parkinsonism, a tauopathy.

STUDY OBJECTIVE: To describe sleep characteristics and rapid eye movement (REM) sleep behavior disorder in patients with Guadeloupean atypical parkinsonism (Gd-PSP), a tauopathy resembling progressive supranuclear palsy that mainly affects the midbrain. It is possibly caused by the ingestion of sour sop (corossol), a tropical fruit containing acetogenins, which are mitochondrial poisons. DESIGN: Sleep interview, motor and cognitive tests, and overnight videopolysomnography. PATIENTS: Thirty-six age-, sex-, disease-duration- and disability-matched patients with Gd-PSP (n = 9), progressive supranuclear palsy (a tauopathy, n = 9), Parkinson disease (a synucleinopathy, n = 9) and controls (n = 9). SETTINGS: Tertiary-care academic hospital. RESULTS: REM sleep behavior disorder was found in 78% patients with Gd-PSP (43% of patients reported having this disorder several years before the onset of parkinsonism), 44% of patients with idiopathic Parkinson disease, 33% of patients with progressive supranuclear palsy, and no controls. The percentage of muscle activity during REM sleep was greater in patients with Gd-PSP than in controls (limb muscle activity, 8.3%+/-8.7% vs 0.1%+/- 0.2%; chin muscle activity, 24.3%+/- 23.7% vs 0.7%+/-2.0%) but similar to that of other patient groups. The latency and percentage of REM sleep were similar in patients with Gd-PSP, patients with Parkinson disease, and controls, whereas patients with progressive supranuclear palsy had delayed and shortened REM sleep. CONCLUSION: Although Gd-PSP is a tauopathy, most patients experience REM sleep behavior disorder. This suggests that the location of neuronal loss or dysfunction in the midbrain, rather than the protein comprising the histologic lesions (synuclein versus tau aggregation), is responsible for suppressing muscle atonia during REM sleep. Subjects with idiopathic REM sleep behavior disorder should avoid eating sour sop.

Nonvisual responses to light exposure in the human brain during the circadian night.

The brain processes light information to visually represent the environment but also to detect changes in ambient light level. The latter information induces non-image-forming responses and exerts powerful effects on physiology such as synchronization of the circadian clock and suppression of melatonin. In rodents, irradiance information is transduced from a discrete subset of photosensitive retinal ganglion cells via the retinohypothalamic tract to various hypothalamic and brainstem regulatory structures including the hypothalamic suprachiasmatic nuclei, the master circadian pacemaker. In humans, light also acutely modulates alertness, but the cerebral correlates of this effect are unknown. We assessed regional cerebral blood flow in 13 subjects attending to auditory and visual stimuli in near darkness following light exposures (>8000 lux) of different durations (0.5, 17, 16.5, and 0 min) during the biological night. The bright broadband polychromatic light suppressed melatonin and enhanced alertness. Functional imaging revealed that a large-scale occipito-parietal attention network, including the right intraparietal sulcus, was more active in proportion to the duration of light exposures preceding the scans. Activity in the hypothalamus decreased in proportion to previous illumination. These findings have important implications for understanding the effects of light on human behavior.