Please refer to specific syndromes and etiologies in which this seizure type occurs for specific information. As a general rule, EEG abnormality may be enhanced in sleep deprivation states and in sleep. In some syndromes/etiologies, photic stimulation and/or eye closure may enhance EEG abnormalities.
In occipital structural brain abnormality, background posterior dominant alpha rhythms and photic driving responses may be asymmetric in amplitude; the interictal EEG may or may not show interictal epileptiform abnormality (spike-and-wave or sharp slow waves).
In Panayiotopoulos syndrome, occipital spike-and-wave may be of high voltage.
In occipital structural brain abnormality, the ictal EEG can be unhelpful and may vary with seizure spread, which may be to the temporal or frontal lobes or bilaterally. A localized (lobar) or lateralized (hemispheric) ictal rhythm may not be present in up to 20% of patients. Generalized epileptiform abnormalities are common and may exhibit bilateral asynchrony. Ictal rhythms when present may be characterized by occipital paroxysmal fast activity or rhythmic spike activity, which may be preceded by brief attenuation of the EEG.