EEG recordings in the course of recovery from stroke

This study was designed to assess the value of quantified electroencephalography (EEG) in the follow-up of stroke and its possible correlation with other measures of recovery.

EEGs were recorded over a period of 6 months in 34 patients with ischemic stroke in the middle cerebral artery territory who underwent spectral analysis. Two groups were formed: (1) 28 patients with a Barthel Index score of less than 60 at admission and (2) 6 patients with a Barthel score of over 60 and therefore with a much better prognosis. Ten recordings were made in each patient in the first group and at least three in the second group. Motor functions and activities of daily living (ADL) were assessed three times, on admission to the study and after 3 and 6 months.

Quantified EEG was significantly abnormal in the affected hemisphere of the first group. Side and site were not relevant. Longitudinal recordings showed a significant improvement of the power spectrum in the first 3 months. Alpha mean weighted frequency of the injured hemisphere was always slower than that of the contralateral side. All patients improved in motor performance and ADL, with the greatest gain in the first 3 months. However, no correlation between quantified EEG and clinical testing was found. By looking at individual profiles, a frequent and unpredictable instability was seen in the "unaffected" hemisphere. In those who made the best recovery, the EEG spectrum became more symmetrical over the left and right hemispheres, an aspect that continued beyond the point of a good motor and ADL recovery.

Quantified EEG undergoes early and subtle changes in the follow-up of stroke that can outlast clinical recovery. Routine evaluation for prognosis is not recommended because motor and ADL scales provide earlier and more accurate indicators. In contrast, quantified EEG can be useful for individual patients undergoing rehabilitation to monitor mechanisms of local repair and also to detect changes in the so-called normal hemisphere. It may reveal focal abnormalities that are undetected by coarse clinical evaluation and that call for appropriate neuropsychological testing.