Eectroencephalogram in "locked-in" syndrome.

Twenty-three EEG studies in eight patients with "locked-in" syndrome were reviewed. The EEG was either normal or minimally slow in all except one patient. All showed reactivity to various stimuli. Photic stimulation elicited a photic driving response at one time or another in all the seven patients where it was attempted. Althouth the basic activity may be similar, it is the preservation of alertness and the presence of reactivity of the EEG which distinguishes the "locked-in" patients from those comatose due to an extensive brain stem lesion. In an unresponsive patient, an EEG resembling that of the waking state, although highly suggestive of an intrinsic brain stem insult, may also occur at times in association with diffuse cortical damage, secondary to prolonged cardio-pulmonary arrest.