How valid is the clinical diagnosis of Parkinson's disease in the community?

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Abstract
In a population based study on the prevalence of Parkinson’s disease in London, Schrag et al reported on the data of a long term clinical evaluation of 202 patients.1 The initial diagnosis of probable Parkinson’s disease was later confirmed in 83%, plus 2% each with atypical features and possible Parkinson’s disease. In 15% the initial diagnosis was later rejected, while 19% of patients not diagnosed as Parkinson’s disease were later found to have the disorder. Their conclusion was that in 15% of the cases the clinical criteria of Parkinson’s disease were not followed, in accordance with previous retrospective clinicopathological studies of parkinsonism, in which the rate of false positive diagnosis ranged between 22–24%2,3 and 15–18%.4,5 Using more strict diagnostic criteria by movement disorder experts, this figure could recently be further reduced to around 10%, with a positive predictive value (PPV) for idiopathic Parkinson’s disease of 98.6%, and for other parkinsonian syndromes 71.4%—for example, for multisystem atrophy (MSA), 85.7%, and for progressive supranuclear palsy (PSP), 80%.6,7 Referring …