Mesial temporal sclerosis (MTS) is a chronic neurological condition characterized by the hardening or scarring of brain tissue in the temporal lobe. This condition is a common cause of epilepsy, particularly forms that do not respond well to medication.
Understanding Mesial Temporal Sclerosis
The term “mesial temporal” refers to the inner part of the temporal lobe. This area includes structures such as the hippocampus, amygdala, and parahippocampal gyrus, which are involved in memory and emotions. “Sclerosis” describes the pathological change where normal brain tissue is replaced by hardened, scarred tissue due to neuronal cell loss and gliosis, which is the proliferation of glial cells in response to injury.
This scarring disrupts the normal electrical activity of these brain areas. Neurons in the affected regions become hyperexcitable, meaning they are more prone to generating abnormal electrical discharges. This heightened excitability leads to recurrent, unprovoked seizures. The hippocampus, being particularly vulnerable, is often the primary site of this scarring, a condition sometimes specifically referred to as hippocampal sclerosis.
Causes and Risk Factors
Mesial temporal sclerosis is generally considered an acquired condition. One of the most frequently associated factors is a history of prolonged febrile seizures, especially those occurring in early childhood. These are seizures accompanied by a fever, potentially leading to acute hippocampal injury that can evolve into sclerosis over time.
Other contributing factors can include head trauma. Central nervous system infections, such as meningitis or encephalitis, are also recognized risk factors. Conditions that lead to a lack of oxygen to the brain, or even strokes, can contribute to sclerosis in the temporal lobe. In some instances, a genetic predisposition may play a role, particularly when there is a family history of similar seizure disorders.
Recognizing the Signs
Mesial temporal sclerosis primarily manifests through characteristic types of seizures. These can include focal aware seizures, where consciousness is maintained, and focal impaired awareness seizures, where awareness is altered. Individuals might experience auras, which are warning sensations preceding a seizure, such as a rising feeling in the stomach, fear, anxiety, or unusual tastes and smells.
Common seizure manifestations also include automatisms, which are repetitive, involuntary movements like lip-smacking, fumbling with clothes, or behavioral arrest where movement ceases. There can be a sense of déjà vu (a feeling of having already experienced something) or jamais vu (a feeling of unfamiliarity with a familiar situation). While seizures typically remain focal, they can sometimes spread to involve the entire brain, resulting in a generalized seizure. Beyond seizures, individuals may experience non-seizure symptoms such as memory problems, particularly with forming new memories, and mood disturbances like depression or anxiety.
Diagnosis and Management Approaches
Diagnosing mesial temporal sclerosis involves clinical evaluation and specialized imaging. A patient history, including any past febrile seizures or head injuries, is gathered. Magnetic resonance imaging (MRI) is a primary diagnostic tool, capable of detecting characteristic changes such as hippocampal atrophy (shrinkage) and increased signal intensity in the affected area, indicating scarring.
Electroencephalography (EEG) records the brain’s electrical activity and can identify abnormal epileptiform discharges originating from the temporal lobe, supporting diagnosis. Video-EEG monitoring can capture seizure events and correlate them with brain wave patterns. Neuropsychological testing may also be conducted to assess memory and cognitive functions, revealing patterns consistent with temporal lobe dysfunction.
The management of mesial temporal sclerosis primarily aims to control seizures and improve quality of life. Treatment often begins with anti-seizure medications (ASMs) to reduce seizure frequency and severity. However, for many individuals with MTS, seizures may become drug-resistant, meaning they do not respond adequately to multiple medications.
For cases of drug-resistant epilepsy, surgical intervention is often considered a highly effective treatment option. Procedures such as temporal lobectomy (removing the affected temporal lobe) or selective amygdalohippocampectomy (targeted removal of the scarred hippocampus and amygdala) can lead to significant seizure reduction or even freedom from seizures. Other advanced options include laser interstitial thermal therapy (LITT), vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation (RNS), offering alternative ways to modulate seizure activity. A multidisciplinary team of neurologists, neurosurgeons, and other specialists typically collaborates to determine the most appropriate management strategy for each individual.