Temporal Lobe Epilepsy - Causes

Causes

A link between febrile seizures (seizures coinciding with episodes of fever in young children) and subsequent temporal lobe epilepsy has been suggested, but the exact role remains unclear. Some studies have shown abnormalities of the hippocampus on magnetic resonance imaging (MRI) in status epilepticus, which supports the theory that prolonged seizures damage the brain. Interestingly, some cases of MTLE present without the typical changes of mesial temporal sclerosis or other abnormalities on MRI scans. This has been termed paradoxical mesial temporal lobe epilepsy. The epilepsy in these patients tends to occur at a later age, which might suggest that an early event leads to hippocampal damage causing MTLE. Although this theory needs confirmation, some studies have pointed to human herpesvirus 6 (HHV-6) as a possible link between febrile convulsions and later MTLE. Some studies suggest that HHV-6 infection happens prior to the occurrence of febrile seizures. However, only a minority of primary HHV-6 infections may be associated with febrile seizures. Secondly, other studies found HHV-6 DNA in brain tissue removed during surgery for MTLE.

Rarely, MTLE can be hereditary or related to brain tumors, spinal meningitis, encephalitis, head injury or blood vessel malformations. MTLE can occur in association with other brain malformations. Most often, a cause cannot be determined with certainty.

LTLE is less common. It can be hereditary, as in Autosomal Dominant Lateral Temporal Lobe Epilepsy (ADLTLE) with auditory or visual features, but can also be associated with tumors, meningitis, encephalitis, trauma, vascular malformations or congenital brain malformations. Again, in many affected persons it is common that no cause can be identified.

Dispersion of granule cell layer in the hippocampal dentate gyrus is occasionally seen in temporal lobe epilepsy and has been linked to the downregulation of reelin, a protein that normally keeps the layer compact by containing the neuronal migration. It is unknown whether changes in reelin expression play a role in epilepsy.