Relationship between slowing of the EEG and cognitive impairment in Parkinson disease.

A previous study using the quantitative EEG technique confirmed that diffuse slowing of the EEG is present in Parkinson disease. The present study was the first to assess the relationship between cognitive impairment and quantitative EEG in Parkinson disease. A total of 100 patients with Parkinson disease with a mean Hoehn-Yahr stage of 2.68 were serially enrolled. Cognitive impairment was assessed using the Mini-Mental State Examination. Lack of ischemic lesions was confirmed in all the patients by MRI. Absolute power values were measured for four frequency bands from δ to β. The electrodes were divided among six locations as follows: frontal pole and frontal, central, parietal, temporal, and occipital locations. Spectral ratio was calculated as the sum of power values for the α- and β-waves divided by the sum of values for slow waves. The relationship between Mini-Mental State Examination score and spectral ratio was assessed by the Jonckheere-Terpstra trend test. At all electrode locations, spectral ratio significantly decreased with a decline in Mini-Mental State Examination score (frontal pole, P = 0.017; frontal, P = 0.028; central, P = 0.019; parietal, P = 0.004; temporal, P = 0.002; occipital, P = 0.006). The rate of patients with Parkinson disease with slowing of the EEG was more frequent with serious cognitive impairment.