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In a previous study,we demonstrated that patients with MPTP-induced parkinsonism(MPTP-IP)had a pattern of cognitive change similar to that in nondemented patients with idiopathic Parkinson's disease(PD).The present study addressed cognitive change in MPTP-exposed but relatively asymptomatic(MPTP-AS)individuals.We examined them for general intellectual function,construction,language,memory,executive function,attention,and reaction time,and compared their performance with data obtained in the previous study from patients with MPTP-IP and drug addict controls.Each MPTP-AS individual had some subtle parkinsonian signs,but in no case would these be sufficient for a diagnosis of PD.PET studies showed that these individuals had significantly reduced uptake of labeled 6-fluorodopa into the striatum.MPTP-AS and MPTP-IP groups performed comparably and were significantly worse than controls on tests of construction and category naming.The MPTP-AS group performed at a level between the other 2 groups on a test of executive function.The 3 groups performed comparably on all other measures.The similarity of the pattern of intellectual change in MPTP-AS to that seen in MPTP-IP and idiopathic PD supports the idea that the dopamine system mediates a specific set of cognitive functions and suggests that cognitive change can occur in the presence of few or no motor signs of parkinsonism. |
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