QUANTITATIVE ELECTROENCEPHALOGRAPHY IN IDIOPATHIC NORMAL-PRESSURE HYDROCEPHALUS - RELATIONSHIP TO CSF OUTFLOW RESISTANCE AND THE CSF TAP-TEST

Quantitative electroencephalography from the occipito-parietal region, gait, and psychometric tests were performed in patients with idiopath ic normal pressure hydrocephalus (NPH) before and after drainage of 40 ml CSF. The results were compared to those in demented controls. The EEG results were also analyzed with respect to possible correlations w ith clinical, CSF dynamics, and psychometric variables. Significant di fferences between NPH patients and demented controls were not found ne ither in baseline EEG variables nor regarding the CSF tap-test-related change in EEG. The EEG-response to the CSF tap-test did not often exc eed the day-to-day test-retest variability. In NPH patients, EEG slowi ng (relative delta and theta power) correlated significantly with CSF outflow-resistance (p<0.002). Relative theta power correlated with the Thurstone's Identical Forms test (p<0.05). Significant correlations b etween EEG and Bingley's Memory Test were found for the control group but not among NPH patients (p<0.05). Thus, EEG band-power variables se em to reflect some of the pathophysiology involved in idiopathic norma l pressure hydrocephalus, particularly increased resistance to CSF out flow. The practical value of the presently applied EEG method in NPH-d iagnosis and prognostic evaluation seems to be limited, however.