Zeta waves: a distinctive type of intermittent delta wave studied prospectively

Zeta waves are a distinctive form of sharply contoured biphasic delta waves that have been associated with underlying structural lesions. We have prospectively interpreted the EEGs of 840 consecutive patients blinded for clinical details. Thirty three patients had zeta waves in at least one recording and 87% of these had an underlying structural lesion on neuroimaging. By excluding those with bifrontal intermittent rhythmic delta activity and bifrontal zeta waves, the positive predictive value of zeta waves for an underlying structural lesion increases to 96%. We conclude that zeta waves are distinctive and easily recognisable delta waves which are highly predictive of recent or residual cerebral damage from a variety of causes, including cerebral trauma and infarction.