Neuropsychological impairments associated with severity of Parkinson's disease.

Intellectual impairment and disease severity tend to parallel one another in patients with Parkinson's disease (PD), but the pattern of development of the neuropsychological impairments contributing to the overall intellectual decline is unknown. This problem was addressed by comparing neuropsychological performance in the early and later stages of PD. Impairment of recent memory, impairment of cognition, and somatic features of depression were seen early and worsened with more advanced disease. Impairment of visuospatial skills, remote memory, language, and mood were observed only in the later stages of PD. These findings suggest that neuropsychological impairments do not develop in a uniform manner with progression of PD.