Smoking and Parkinson's disease. Search for a dose-response relationship.

We tested the hypothesis that the inverse association of smoking and Parkinson's disease (PD) results from a direct pharmacologic benefit of smoking on PD. We mailed questionnaires to the 32,000 members of the United Parkinson Foundation and searched for evidence of a dose-response effect between increasing intensity of smoking and decreasing intensity of PD. Of the 6006 respondents, 3693 met our diagnostic criteria. Despite confining the analysis to subgroups where confounding effects would be minimized, we found no significant correlation between any measure of smoking and any measure of PD severity and conclude that smoking is probably not of benefit in preventing, delaying, or ameliorating PD.

Dopamine-related personality traits in Parkinson's disease.

Studies suggest that Parkinson's disease (PD) is associated with a particular group of personality characteristics. With relative uniformity, PD patients are described as industrious, rigidly moral, stoic, serious, and nonimpulsive. In this controlled study, we used a recently developed personality questionnaire, Cloningers's Tridimensional Personality Questionnaire, to test the hypothesis that these personality traits are behavioural manifestations of damaged dopaminergic pleasure and reward systems. We found significantly less (p < 0.01) of a group of traits called "novelty seeking" in PD patients compared with matched medical controls. Patients with low novelty seeking are described as being reflective, rigid, stoic, slow-tempered, frugal, orderly, and persistent, characteristics similar to those in the clinical description of PD patients. We review evidence supporting the claim that novelty seeking is dopamine-dependent, and suggest that damage to the mesolimbic dopaminergic system causes the described personality profile of PD patients.