Medial temporal lobe epilepsy (MTLE) is the most common form of focal epilepsy, a condition where seizures originate in a specific area of the brain rather than affecting the entire brain simultaneously. This neurological disorder stems from abnormal electrical activity within the medial temporal lobe, a region situated deep within the brain.
Defining Medial Temporal Lobe Epilepsy
Medial temporal lobe epilepsy arises from abnormal electrical discharges within the brain’s temporal lobes, specifically affecting the inner, or mesial, structures. This includes the hippocampus, the amygdala, and the parahippocampal gyrus. The hippocampus, a seahorse-shaped structure, plays a significant role in learning and the formation of new memories. The amygdala, located near the hippocampus, is associated with processing emotions, particularly fear, and emotional memories. The parahippocampal gyrus, which surrounds the hippocampus, is also involved in memory encoding and retrieval.
When neurons in these regions experience uncontrolled bursts of electrical signals, it disrupts their normal function, leading to a seizure. Unlike generalized epilepsies that involve widespread brain activity from the onset, MTLE is characterized by its focal origin, meaning the seizure activity begins in one confined area before potentially spreading.
Recognizing Its Seizure Manifestations
Seizures associated with medial temporal lobe epilepsy often present with distinct patterns, varying in how awareness is affected. Focal aware seizures, previously known as simple partial seizures, occur when an individual remains conscious and aware throughout the event. During these seizures, individuals might experience a range of sensory or emotional phenomena known as auras, which serve as an initial warning. These auras can include feelings of déjà vu, a sense of unfamiliarity (jamais vu), sudden fear, or a rising sensation in the stomach. Some people also report unusual smells or tastes.
Focal impaired awareness seizures, formerly termed complex partial seizures, involve a temporary alteration or loss of consciousness. During these seizures, individuals may appear to stare blankly and become unresponsive to their surroundings. They might engage in repetitive, non-purposeful movements called automatisms, such as lip-smacking, chewing, fumbling with clothes, or repetitive hand movements. The seizure typically lasts between 30 seconds to two minutes.
Following a seizure, individuals often enter a post-ictal phase, characterized by confusion, disorientation, and fatigue. They might have difficulty speaking or recalling what occurred during the seizure.
Underlying Causes and Risk Factors
The causes of medial temporal lobe epilepsy can be diverse, though in many instances, the precise reason remains unidentified. The most frequently identified cause is hippocampal sclerosis, also known as mesial temporal sclerosis. This condition involves scarring and shrinkage of the hippocampus, which can disrupt its normal electrical activity and lead to seizure generation.
Beyond hippocampal sclerosis, several other factors can contribute to the development of MTLE. These include severe head injuries, which can cause structural damage to the temporal lobe. Central nervous system infections, such as meningitis or encephalitis, are also implicated as they can lead to inflammation and damage within brain tissues. Birth complications that result in oxygen deprivation to the brain during development may also increase the risk.
Brain tumors located in or near the temporal lobe can also trigger seizures by interfering with normal brain function. While less common, certain genetic predispositions can play a role in some cases of MTLE. Despite these known associations, it is important to note that a significant number of MTLE cases do not have an identifiable underlying cause.
Diagnosis and Management Strategies
Diagnosing medial temporal lobe epilepsy involves a comprehensive evaluation to pinpoint the seizure origin and rule out other conditions. A detailed medical history, including descriptions of seizure events from the individual and any witnesses, is collected. A neurological examination assesses brain and nervous system function. Electroencephalography (EEG) is a primary diagnostic tool, measuring electrical activity in the brain to detect abnormal patterns characteristic of seizures originating in the temporal lobes. Findings on an EEG, such as sharp waves in the anterior temporal regions, can indicate MTLE.
Magnetic resonance imaging (MRI) of the brain is frequently performed to visualize structural abnormalities, such as hippocampal sclerosis, which is a common finding in MTLE. Management of MTLE often begins with anti-epileptic drugs (AEDs), which are effective in controlling seizures for many individuals. These medications work by stabilizing electrical activity in the brain. For those whose seizures are not adequately controlled by medication, epilepsy surgery, specifically a temporal lobectomy, may be considered as a potentially curative option. This procedure involves surgically removing the affected part of the temporal lobe where seizures originate.
Other therapies are available for suitable candidates, including vagus nerve stimulation (VNS), which involves implanting a device that sends electrical pulses to the vagus nerve to reduce seizure frequency. Dietary therapies, such as the ketogenic diet, are also explored in some cases, particularly for individuals who do not respond well to medications or are not candidates for surgery.