Whilst generalised seizures may start deep in the brain, usually surfacing in both hemispheres simultaneously, focal seizures start within localised networks in a region of the brain (usually one hemisphere) and may stay localised or may spread.
The focal seizure is usually described in terms of where in the brain it starts e.g. frontal lobe, temporal lobe, parietal lobe, occipital lobe (and right or left hemisphere).
Seizures in different lobes have different symptoms during the seizure, and this relates to what function is normally controlled by the area of the brain where the seizure is happening.
For example, the frontal lobe controls movement of the opposite side of the body, and speech.
Frontal lobe seizures may result in retained awareness, but jerking of the opposite arm or leg, or difficulty in speaking.
The temporal lobe controls certain memory functions. Seizures here can cause confusion and loss of memory for the period of the seizure.
Seizures where there is confusion and loss of memory are called dyscognitive seizures (focal dyscognitive seizures would have previously been known as complex partial seizures or psychomotor seizures).
Seizures arising from the midline region of the temporal lobe can cause sensations of fear, sensations in the tummy, pallor and nausea.
Sometimes automatic movements (known as automatisms) may be seen – such as lips smacking or chewing and fumbling with clothes.
Parietal lobe seizures may cause sensory disturbances in the opposite side of the body and occipital lobe seizures may cause visual disturbances, again in the opposite visual field.
Your doctor will ask about information around the symptoms that were experienced or observed during a person’s seizure so that they can try and work out where the seizures are coming from.
Focal seizures evolving to a bilateral convulsive seizure:
- It is not uncommon for focal seizures to spread to become generalised. (Usually a tonic clonic seizure).
- If this happens, it is important to note how the seizure starts.
Dr. Kate Riney, Consultant Paediatric Neurologist & Epileptologist, Senior Lecturer, University of Qld.