Focal epilepsy syndromes are described in terms of the part of the brain that is involved at the onset of the seizures (the seizure focus). Many focal seizures arise in the temporal lobe. However, seizures can also arise in other lobes of the brain. Seizures with a known cause such as a brain malformation are most common. For this reason, a child with focal seizures will be assessed carefully and may have an MRI to locate the source of the seizures.
However, some have no identified cause. There may be a genetic cause in some children. Hence, genetic testing is also recommended to understand the cause of seizures.
Frontal lobe epilepsy
Frontal lobe epilepsy is a very common cause of focal epilepsy in children. The motor cortex is located in the frontal lobe, so focal motor seizures are an example of frontal lobe epilepsy. These usually involve twitching of the face that may spread to the arm and leg on the same side of the body.
Frontal lobe seizures usually begin and end quickly and often happen at night. A child with this type of seizure may have many brief seizures, often in clusters of several seizures. They may turn their eyes and head to one side or raise one arm and may cry out. Status epilepticus is common in frontal lobe epilepsy.
There are few well-defined frontal lobe seizure syndromes. One syndrome that has been identified is autosomal dominant nocturnal frontal lobe epilepsy, a rare syndrome with a well-defined genetic basis. In this scenario, there is a family history of frontal lobe seizures in different family members.
Parietal lobe epilepsy
Parietal lobe epilepsy is quite rare. The sensory cortex is located in the parietal lobe, so focal somatosensory seizures are an example of parietal lobe epilepsy. Most seizures that begin in the parietal lobe start with a sensory aura, such as tingling and numbness. Some people may feel pain in the affected area or may feel that one hand or foot is moving or is not there. Parietal lobe epilepsy is often caused by benign tumours in the parietal lobe.
Occipital lobe epilepsy
Occipital lobe epilepsy is also rare. Children with occipital seizures often see flashing lights or simple shapes that are not there or may not be able to see anything during the seizure. The child’s eyes and head may turn to one side.
In some children with occipital lobe epilepsies, there is no structural abnormality in the brain, and there is an underlying genetic basis. This condition is known as childhood occipital visual epilepsy (COVE), a rare epilepsy syndrome primarily affecting children and adolescents, characterized by frequent, brief, focal sensory seizures with visual phenomena during wakefulness. It used to be called idiopathic childhood occipital epilepsy-Gastaut type or late-onset benign childhood occipital epilepsy. These seizures are often followed by headache with migraine-like features.
Epilepsy involving more than one lobe of the brain
Finally, seizures often affect regions of the brain where two lobes meet. This can result in signs and symptoms that are different than those seen in focal epilepsies which arise from one lobe of the brain. Determining the seizure onset areas is not always easy for the health-care team, and it requires a very detailed description of the seizures by the caregivers and patients, as well as interpretation of electroencephalogram (EEG) and an MRI scan.
Treatment
Children with focal epilepsy will undergo an MRI to determine if there is an underlying structural abnormality, such as a malformation of cortical development or a tumour causing the epilepsy.
If the MRI is normal, then anti-seizure medications may be sufficient to control seizures.
If the MRI shows an underlying abnormality, an epilepsy surgery is usually needed. Children with a normal MRI who continue to have seizures, despite two or three anti-seizure medication trials, will also require an epilepsy surgery work-up, as they may have a subtle malformation that is not seen on the MRI.