Zeta waves, an unusual EEG finding in structural brain lesions: report of two patients

We report two patients with acute cerebral conditions and zeta waves on their EEGs. The first patient, a 48-year-old lady, had acute disseminated encephalomyelitis (ADEM)following afebrile illness. Neurological examination showed expressive dysphasia and a mild right hemiparesis. The magnetic resonance imaging (MRI) scan of the brain showed multiple, bilateral, subcortical white matter hyperintensities, predominantly in the centrum semiovale region of the left hemisphere, and also in the corpus callosum. An EEG done 21 days after the onset of the neurological deficit showed intermittent, sharply contoured, predominantly biphasic delta waves (zeta waves) over the left frontotemporal region. The second patient was a 2-year-old child, who had a head-injury resulting in bilateral, frontoparietal fractures of the skull; acute epidural hematoma on the left frontoparietal region; and a cerebral contusion on the right frontotemporal region. An EEG done one day after the evacuation of the hematoma showed zeta waves over the right frontal region. To the best of our knowledge, the association of zeta waves and ADEM has not been previously reported. The EEG findings in our patients again supports the hypothesis that these waves are seen predominantly in patients with structural brain lesions. Other conditions causing zeta waves in the EEG are briefly reviewed.