Clinical and biochemical correlates of bradyphrenia in Parkinson's disease.

Bradyphrenia is considered the mental equivalent of bradykinesia in Parkinson's disease. Patients are described as inattentive and "slow thinking," but not demented. We compared the performance of three groups: parkinsonians age-matched controls, and mildly impaired patients with probable Alzheimer's disease in tests of general intellect, memory reaction time, and in a continuous performance task measuring attention and vigilance. Metabolites of the major biogenic amine in CSF were also measured. The parkinsonians formed two distinct groups. In one, intellectual function and CSF measures were similar to that of controls. The other group of parkinsonians had significantly more omission errors and fewer correct response on the continuous performance task than did controls or patients with Alzheimer's disease. We considered this second group to have bradyphrenia. Their performance on measures of general intellectual and memory function was similar to that of the patients with Alzheimer's disease. CSF-MHPG, the major metabolite of norepinephrine, correlated with the continuous performance task and reaction time in all parkinsonians, and those with bradyphrenia had the highest CSF-MHPG levels. Our data suggest that bradyphrenia is an impairment of attention and vigilance, unique to Parkinson's disease, that may be associated with dementia and with an alteration in norepinephrine metabolism.