What are the causes of epilepsy?

Structural epilepsies

These epilepsy are the result of a diffuse or local brain injury resulting in generalized or focal seizures. The lesion is most often visible on a brain MRI (this may be called a symptomatic lesion). Sometimes it is not visible (it can be called a cryptogenic lesion). There is a wide range of injuries:

• Hippocampal sclerosis is a scar found in the hippocampus, a structure involved in memory, which is often the result of repeated episodes of epileptic seizures in the context of childhood fever.
• A brain tumour, affecting the cerebral cortex
• A sequelae of stroke, affecting the cerebral cortex
• A malformation of the cerebral cortex due to a defect in neuronal migration during development, the most common being focal cortical dysplasia
• A sequelae of head trauma, often severe
• A sequel of infection such as herpes encephalitis, a parasitic infection

Autoimmune epilepsies

Many autoimmune encephalitis is accompanied by seizures. These diseases may lead to:

• the aberrant production of antibodies, which target brain proteins and thus disrupt the functioning of neurons.
• the infiltration into the brain of inflammatory cells, such as lymphocytes, which attack neurons.

Early identification of these diseases allows the administration of immunosuppressive drugs, the only way to reduce seizures.

The Epilepsy Unit headed by Professor Vincent Navarro at the Salpêtrière Hospital, Reference Centre for Rare Epilepsies, has great expertise in the management of these epilepsies, which require rapid assessment and sophisticated examinations.

Research has recently been carried out in the research team ‘Dynamics of epileptic networks and neuronal excitability’, at Paris Brain Institute, by Professor Vincent Navarro: the mechanisms of the seizures observed in autoimmune encephalitis linked to an LGI1 antibody have been elucidated: the brief twitches of the muscles, arm and face characteristic of this disease are shown to be linked to hyperexcitability of neurons, due to lack of potassium (Baudin et al, Prog Neurobiol 2022).

Genetic epilepsies

There are several forms of genetic epilepsy:

• idiopathic epilepsies, presumed to have a genetic cause, since often another person in the family is epileptic, but for which a mutation in a gene has not been identified. Idiopathic epilepsies are defined by the absence of MRI-detectable brain damage, a characteristic onset age, a good response to anti-epileptic therapy, and most often remission after several years. The electroencephalogram shows typical abnormalities. They can be focal or generalized.
• family epilepsies due to mutations identified in genes.

Depending on the mutated gene, brain abnormalities can be identified, such as the Bourneville bluebird. When mutated genes encode ion channels (proteins that form tunnels that allow ions such as sodium and potassium to pass through the neuron), no abnormalities are detectable on MRI. Mutations in neurotransmitter receptors have also been identified.

Epileptic seizures “Situational”

Sometimes a seizure occurs in a particular context, when there is no underlying brain injury or long-term susceptibility to recurrence of seizures. In such a situation, long-term correction of the disorder is sufficient, and long-term antiepileptic therapy is not necessary.

• An excessive and unusual dose of alcohol, withdrawal or chronic alcoholism.
• Use of cocaine or amphetamines
• The use of pro-convulsant drugs
• Hypoglycemia (lack of sugar)
• Hypocalcemia (lack of calcium)
• Hyponatremia (lack of sodium)