How specific are periodic complexes in the diagnosis of herpes simplex encephalitis?

The specificity of localized periodic complexes (PC) in the EEG is discussed by means of a case. This patient presented rapidly evolving focal symptoms of the CNS together with fever. The EEG showed localized PCs and in the CT scan there was a hyperdense lesion in a region corresponding to the EEG finding. Postmortem examination revealed a subcortical bleeding in the temporal region. Possible mechanisms for the origin of these PCs and their diagnostic value are discussed.