Spectral EEG parameters in patients with tick-borne encephalitis: a follow-up study

Follow-up of spectral EEG parameters were reported for five patients with serologically verified tick-borne encephalitis. Comparisons were made for clinical data and findings of EEG analysis (power probability mapping, peak-power frequencies, and alpha/theta power ratios) were compared. A prominent feature of the EEG abnormality was the marked attenuation of background alpha activity. The peak-power frequency and absolute power analysis of three patients showed significant hemispheric asymmetry in the alpha and theta bands respectively. EEG topograms demonstrated persistent theta power fields in one patient. Alpha/theta power ratio was a reliable indicator for the recovery of rhythmic EEG activity during the convalescence. Reorganization of alpha activity appeared to lag behind the clinical improvement, its course was different from patient to patient. Because of the discrepancy of bioelectric and clinical findings the authors recommend long-term EEG monitoring in patients with tick-borne encephalitis.