Electrophysiological differences between demented and nondemented patients with Parkinson's disease.

Long-latency auditory evoked potentials were studied in demented and nondemented patients with Parkinson's disease who were matched for age, stage of disease, duration of illness, and amount and nature of antiparkinsonian medication. We found clear electrophysiological differences between the two groups of patients in that the N1, N2, and P3 peak latencies were prolonged in the demented group compared both to the nondemented group and to normal controls. Moreover, the N1 latency but not the N2 and P3 latency prolongation distinguished the demented parkinsonian patients from demented patients with Alzheimer's disease. These results provide strong evidence for the existence of different subtypes of dementia and suggest that electrophysiological recordings may be helpful in establishing the underlying pathogenesis of a dementia syndrome when there is clinical uncertainty.