Page 156 - ILAE_Lectures_2015

Chapter 15

Occipital and parietal lobe epilepsies

JOHN S. DUNCAN

UCL Institute of Neurology, National Hospital for Neurology and Neurosurgery, Queen
Square, London

Epileptic seizures of parietal and occipital origin are heterogeneous and mainly characterised
by the presenting auras, although the most dramatic clinical manifestations may reflect
spread, and overshadow the focal origin. The two lobes serve mainly sensory functions, and
the characteristic seizure phenomena are therefore subjective sensations. The incidence of
these seizures is not well known, but they are generally considered rare. Occipital seizures
have been reported to constitute 8% and parietal seizures 1.4% of total seizures in the
prevalent population with epilepsy1,2. The pattern of seizures is most commonly focal seizures
without impairment of awareness, with occasional secondary generalisation. Focal seizures
with impairment of awareness are rare and usually indicate spread of the seizure into the
temporal lobe.

Seizures with somatosensory symptomatology1-3

Somatosensory seizures may arise from any of the three sensory areas of the parietal lobe,
but the post-central gyrus is most commonly involved. Seizures present with contralateral, or
rarely ipsilateral, or bilateral sensations. All sensory modalities may be represented, most
commonly tingling and numbness, alone or together. There may be prickling, tickling or
crawling sensations, or a feeling of electric shock in the affected body part. The arms and the
face are the most common sites, but any segment or region may be affected. The paraesthesia
may spread in a Jacksonian manner, and when this occurs motor activity in the affected body
member follows the sensations in about 50% of cases.

Pain is the second most common somatosensory seizure experience, often described as
stabbing, intense, torturing, agonising or dull. It may be difficult to distinguish the pain from
thermal perception or muscle cramps, which frequently follow the pain. Thermal perceptions
are less common than pain or paraesthesia, and rarely occur without other sensory
phenomena. A burning sensation is more common than the feeling of cold. Contralateral
abdominal pain is also described.

A small subgroup of seizures with sexual phenomenology seems to originate in the
paracentral lobule where the primary somatosensory area for the genitalia is thought to reside,
usually involving the non-dominant hemisphere. The seizures present with a tactile
somatosensory aura affecting the genitalia, but the ensuing seizure may exhibit other features
of sexual behaviour.

A feeling of inability to move is thought to involve the secondary sensory area on the
suprasylvian border. Such seizures may be preceded by a psychic aura (‘psychoparetic’).
Contralateral, ipsilateral, bilateral or midline structures may be affected. Paroxysmal ictal
paralysis may spread in a Jacksonian way and be followed by clonic activity in the same body
part. Other somatosensory features in epilepsy are body image disturbances, such as feeling
of movement or altered posture in a stationary limb, feeling of floating, twisting or even