Relationship of motor symptoms, intellectual impairment, and depression in Parkinson's disease.

The relationship between severity of disease, intellectual impairment, and depression was examined in 50 patients with Parkinson's disease. A significant correlation between severity of disease and intellectual impairment suggests that both may result from the same subcortical lesions. Depression was not significantly related either to severity of disease or to intellectual impairment. This suggests that the relationship between severity of disease and intellectual impairment was not an artifact of increasing depression. Severity of rigidity and of bradykinesia did predict severity of intellectual decline, but severity of tremor predicted better intellectual status. Patients with a predominance of tremor may have a more benign clinical course as well as better intellectual function than patients with a predominance of rigidity and bradykinesia.