The olfactory and cognitive deficits of Parkinson's disease: evidence for independence

In the present study we sought to determine whether the olfactory deficits of parkinsonism are related to the cognitive and perceptual-motor manifestations of the disease. Pearson correlation coefficients were computed among a number of olfactory, neurological, and neuropsychological measures obtained from 58 Parkinson's disease patients, including the University of Pennsylvania Smell Identification Test, a modified Randt memory test, a reaction time test, a finger-tapping test, ratings of motor and neurological function, and selected verbal and performance subtests of the Wechsler Adult Intelligence Scale--Revised. Data from 38 patients with Parkinson's disease who received odor detection threshold testing were also evaluated. The intercorrelation matrix was subjected to a principal components factor analysis which yielded six clear-cut factors: cognitive/memory, gross motor, oral motor, fine motor, olfactory, and tremor. The olfactory factor received strong and nearly exclusive loadings from the olfactory measures (which did not evidence meaningful loadings on any of the other factors). A ten-trial jackknife procedure revealed the factor structure to be stable. Further support of the independence of the olfactory variables from the other measures was provided by multiple regression and canonical correlation analyses. Overall, these findings lend support to the hypothesis that the olfactory disorder of parkinsonism is independent of the cognitive, perceptual-motor, and memory manifestations of the disease.