Clinical Seizure Semiology 2

Introduction

• Ictal discharges originate from the epileptogenic zone and activate the symptomatogenic zone, producing clinical semiology.
• Resective epilepsy surgery requires complete resection of the epileptogenic zone for success.
• Patients with lateralizing auras show better surgical outcomes compared to those without.
• Ictal semiology reflects the involvement of the symptomatogenic zone, not necessarily the ictal onset zone.

Auras

• Somatosensory Auras (SAs):

  • Clear somatotopic distribution indicates activation of the contralateral somatosensory cortex (Brodmann areas 3, 1, 2).
  • Poorly defined paresthesias may result from the supplementary sensorimotor area (SMA).
  • Activation of the superior bank of the Sylvian fissure typically produces distal and bilateral sensations, usually lateralizing but not localizing.

• Painful Auras:

  • Generally contralateral to seizure onset, activated in the postcentral gyrus and parietal lobe.
  • Temporal lobe epilepsy can show ipsilateral sensations due to secondary somatosensory area activation.

• Auditory Auras:

  • Simple sounds indicate Heschl gyrus involvement (Brodmann 41 and 42); complex sounds involve auditory association cortex (Brodmann areas 42 and sometimes 22).
  • Unilateral ear plugging can lateralize to the contralateral temporal lobe; its auditory nature is unclear.

• Olfactory Auras:

  • Strongly localized to mesial temporal structures, typically involving the amygdala, with possible involvement of the orbitofrontal cortex.

• Gustatory Auras:

  • Involve activation of the parietal operculum and mesiobasal temporal lobe; challenging to differentiate from olfactory auras.

• Visual Auras:

  • Simple visual auras suggest occipital seizures (Brodmann 17, 18, 19); static auras usually come from area 17 (V1).
  • Homonymous hemifield defects localize the seizure focus to the contralateral hemisphere.

• Abdominal Auras:

  • Common in mesial temporal seizures; symptomatogenic zone typically in the insula.

• Psychic Auras:

  • Include emotional symptoms and familiarity distortions; fear indicates amygdala activation.
  • Déjà vu sensations usually involve the uncus or entorhinal cortex, while out-of-body experiences involve the temporo-parietal junction.

• Autonomic Auras:

  • Include cardiorespiratory, GI, and cutaneous sensations, activated by various cortical areas, especially the insula.
  • Ictal urge to urinate indicates non-dominant hemisphere involvement.

Lateralizing Ictal Signs

• Head and Eye Deviation:

  • Mostly contralateral to seizure onset; caused by activation of frontal eye fields and adjacent motor areas.

• Unilateral Clonic Activity:

  • Typically contralateral to seizure focus; linked to primary motor area activation.

• Last Clonic Activity:

  • In temporal lobe epilepsy, clonic jerks occur ipsilateral to seizure onset over 80% of the time, likely due to metabolic exhaustion.

• Unilateral Dystonic Posturing:

  • Reliable lateralizing sign in temporal lobe epilepsy, with high contralateral correlation.

• Asymmetric Tonic Posturing:

  • Characterized by one arm extended and the opposite flexed; extended arm is typically contralateral to seizure onset.

• Ictal Speech:

  • Preservation during seizures often lateralizes to the non-dominant hemisphere.

• Ictal Nystagmus:

  • Often related to seizures from the posterior regions; EEG changes usually contralateral to the fast phase.

Lateralizing Post-Ictal Signs

• Todd’s Paralysis:

  • Contralateral to seizure onset, likely due to exhaustion of primary motor areas.

• Postictal Aphasia:

  • Indicates involvement of language-dominant hemisphere, differentiated from postictal confusion.

• Postictal Nosewiping:

  • Common in temporal lobe epilepsy, occurring ipsilateral to the seizure onset in 75-90% of cases; exact mechanism remains unclear.