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.