In Guadeloupe, there is an abnormally high frequency of atypical parkinsonism. 
Only one-third of the patients that develop parkinsonian symptoms were reported 
to present the classical features of idiopathic Parkinson disease and one-third 
a syndrome resembling progressive supranuclear palsy (PSP). The others were 
unclassifiable, according to established criteria. We carried out a 
cross-sectional study of 160 parkinsonian patients to: (i) define more precisely 
the clinical phenotypes of the PSP-like syndrome and the parkinsonism that was 
considered unclassifiable in comparison with previously known disorders; (ii) 
define the neuropsychological and brain imaging features of these patients; 
(iii) evaluate to what extent a candidate aetiological factor, the mitochondrial 
complex I inhibitor annonacin contained in the fruit and leaves of the tropical 
plant Annona muricata (soursop) plays a role in the neurological syndrome. 
Neuropsychological tests and MRI were used to classify the patients into those 
with Parkinson's disease (31%), Guadeloupean PSP-like syndrome (32%), 
Guadeloupean parkinsonism-dementia complex (PDC, 31%) and other 
parkinsonism-related disorders (6%). Patients with a PSP-like syndrome developed 
levodopa-resistant parkinsonism, associated with early postural instability and 
supranuclear oculomotor dysfunction. They differed, however, from classical PSP 
patients by the frequency of tremor (>50%), dysautonomia (50%) and the 
occurrence of hallucinations (59%). PDC patients had levodopa-resistant 
parkinsonism associated with frontosubcortical dementia, 52% of these patients 
had hallucinations, but, importantly, none had oculomotor dysfunction. The 
pattern of neuropsychological deficits was similar in both subgroups. Cerebral 
atrophy was seen in the majority of the PSP-like and PDC patients, with 
enlargement of the third ventricle and marked T2-hypointensity in the basal 
ganglia, particularly the substantia nigra. Consumption of soursop was 
significantly greater in both PSP-like and PDC patients than in controls and 
Parkinson's disease patients. In conclusion, atypical Guadeloupean parkinsonism 
comprises two forms of parkinsonism and dementia that differ clinically by the 
presence of oculomotor signs, but have similar cognitive profiles and 
neuroimaging features, suggesting that they may constitute a single disease 
entity, and both were similarly exposed to annonaceous neurotoxins, notably 
annonacin.