Background/Interictal/Activation

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.

EEG abnormalities (spike-and-wave or sharp slow waves) are seen in an anterior temporal distribution in mesial temporal lobe structural brain abnormality. Focal slow and/or temporal intermittent rhythmic delta activity (TIRDA) can be seen in around half of patients with mesial temporal structural brain abnormality. EEG abnormalities may be seen in a mid-temporal or posterior temporal distribution in lateral temporal lobe structural brain abnormalities.

Ictal

Seizures in mesial temporal lobe structural brain abnormality are characterized by rhythmic theta (or less commonly spike) activity in the anterior temporal EEG leads (F7, T3; F8, T4). The EEG change may follow the clinical seizure onset. Focal post-ictal slow activity occurs in about 70% of such seizures and if present is consistent with side of seizure onset in 90% of seizures.

Seizures in lateral temporal lobe structural brain abnormality are characterized by mid- to posterior temporal ictal rhythms (rhythmic theta or spike activity seen at T3, T5; T4, T6), with a broad field. The ictal rhythmic activity may be less stable in frequency and amplitude than in mesial temporal seizures, bi-temporal spread occurs more often (in up to 20%) and more rapidly.