What is Mesial Temporal Lobe Epilepsy?
The temporal lobes, areas in the brain, are the most likely to develop a condition that can cause seizures, known as “epileptogenicity”. Centuries ago, a phenomenon known as “uncinate fits” was first described by Hughlings Jackson. This term was used to refer to seizures that present as “dreamy states” and are linked to damage in a part of the temporal lobe known as the uncus. Later in the mid 20th century, Gibbs and Gibbs introduced the term “psychomotor epilepsy”, which was used to describe specific mental and emotional symptoms of patients having seizures that originate from the temporal lobes. These symptoms, combined with certain features seen in brain wave studies, were further confirmed by Jasper and Penfield to come from the temporal lobe.
It’s important to mention a unique type of this condition, known as Mesial Temporal Lobe Epilepsy (MTLE). It’s often discussed separately because it has different causes, symptoms, imaging results (pictures from scans like MRI), and brain wave characteristics compared to a similar condition that affects the outer part of the temporal lobe. Furthermore, the inside of the temporal lobes tends to be the starting point for approximately 80% of all these types of seizures.
What Causes Mesial Temporal Lobe Epilepsy?
Most people with Mesial Temporal Lobe Epilepsy (MTLE), a type of epilepsy focused in a specific part of the brain, develop it randomly, but some get it from their family. In fact, one study found that up to 20% of people with new cases of non-lesional MTLE, which does not appear to be caused by any visible brain damage, could have gotten it from their family. Further research identified a specific section of the genes (genetic locus) that could be responsible for MTLE in families. These familial MTLE conditions are often inherited in a complex way and usually don’t show any damage in the inner part of the temporal lobe (mesial temporal sclerosis) when brain scans are taken.
Hippocampal sclerosis (HS), or scarring in the hippocampus region of the brain, is the most common abnormality found in patients with drug-resistant Temporal Lobe Epilepsy (TLE). For example, in a European study involving 9523 patients with epilepsy having surgery, HS was found in 36.4% of patients. Other conditions found included long-term epilepsy-associated tumors (LEAT) in 23.6% of patients, and focal cortical dysplasias (FCD) – developmental malformations in the brain’s outer layer – in 19.8% of patients. Other less common abnormalities included polymicrogyria, nodular heterotopia, and hamartomas, which are rare pathologies associated with temporal lobe epilepsy.
There are also other unusual causes of MTLE, including post-infectious causes (most commonly following a specific type of brain infection caused by the herpes simplex virus), vascular malformations, ischemic lesions (tissue damage caused by lack of blood supply), inflammatory lesions, and old traumatic encephalomalacia (softening of the brain tissue due to injury).
Risk Factors and Frequency for Mesial Temporal Lobe Epilepsy
Mesial Temporal Lobe Epilepsy (MTLE) doesn’t seem to affect a specific age group or sex more than others. Patients usually have a normal history related to birth and development, as well as normal neurological examinations. In addition, they are typically cognitively intact. However, having a history of febrile seizures during childhood appears to be a significant sign of future MTLE development.
One study observed 226 children who have had febrile status epilepticus (a type of seizure triggered by fever). In this group, about 10% showed signs of acute hippocampal injury (damage to a part of the brain). When some of these children were monitored through brain MRI scans, hippocampal sclerosis (a brain condition that can cause seizures) was found in 10 of them, and hippocampal volume loss (shrinking of the same brain part) was found in 12.
There are also other less significant risk factors for developing MTLE, which include:
- Head trauma,
- Birth trauma,
- Infections of the central nervous system during childhood, and
- Infarcts in the posterior cerebral artery territory (blockages in certain brain blood vessels).
Signs and Symptoms of Mesial Temporal Lobe Epilepsy
The International League Against Epilepsy (ILAE) has recently updated the classification system for epilepsy. This new system is crucial for making informed treatment decisions. It now classifies patients with Mesial Temporal Lobe Epilepsy (MTLE) as having focal epilepsy, leading to focal onset seizures with or without impaired awareness.
During these seizures, when the patient is still aware, they often experience unusual sensations called auras. Auras are often difficult to describe, ranging from bodily sensations to psychological experiences. Also, patients might exhibit physical reactions and behavioral changes along with these sensations.
- Visceral, autonomic, or gustatory auras: This could include rising sensations in the stomach or nausea, or even taste or smell hallucinations.
- Affective auras: Psychological experiences like a feeling of being outside the body (depersonalization), feeling of familiarity or unfamiliarity (déjà vu and jamais vu), hearing familiar sounds (déjà entendu), or a rapid recall of past events (panoramic visions). Feelings of joy, absolute fear, or anger might also occur.
- Autonomic reactions: This could be changes in body hair (piloerection), skin color (pallor/flushing), heartbeat (tachycardia), or pupil size (pupillary dilatation).
- Behavioral changes: Patients might unresponsively stare into space, and this could be followed by involuntary facial movements like lip-smacking or chewing, or hand movements like fidgeting or disrobing. There could also be posturing of limbs. Notably, the presence of speech might indicate the seizure started in the non-dominant hemisphere of the brain, however, lack of speech does not conclusively prove otherwise.
After these experiences, patients usually go through a period of confusion. Occasionally, these might escalate into generalized tonic-clonic seizures, which are more severe and affect the whole body.
Testing for Mesial Temporal Lobe Epilepsy
Even with the advancements in seizure controlling medications, people with a type of epilepsy known as MTLE often progressively resist the benefits of these drugs. Studies show that less than 25% of MTLE patients experience a seizure-free life for over a year. Hence, alternative therapies that don’t involve drugs gain importance for people with MTLE. However, these therapies require a precise identification of the part of the brain responsible for causing seizures.
Before doctors can suggest surgery for epilepsy, they need to locate the “epileptogenic zone”, which is the particular area in the brain that triggers seizures. If this area can be successfully removed or controlled, the patient could become seizure-free. This zone isn’t a physical spot but rather a theoretical area which doctors locate by gathering and interpreting data from various sources. These include:
1. EEG and magnetoencephalography (MEG), which measure brain waves
2. MRI scans, PET, and SPECT, which are various imaging techniques
3. Neuropsychological evaluations that assess the functions linked to the affected brain area.
Images from a highly powerful MRI of the brain, particularly focusing on structures in the deep part of the brain (‘mesial temporal structures’), can show even minute alterations in these structures. Other imaging techniques such as PET scans can identify the part of the brain responsible for causing seizures in up to 70 to 90 percent of patients with MTLE. There are also tools available that can provide information about the explosion of activity (like a hyperactivity storm) in the brain that heralds a seizure, and how it spreads along the brain’s network.
The presurgical evaluation for epilepsy has two phases, the first involving non-invasive methods to determine where the seizure originates. This includes video-EEG, MEG, MRI, PET, SPECT, and neuropsychological evaluation. Phase II involves invasive methods such as placement of sensors directly on the brain to determine the exact origin of the seizure.
EEG recordings of patients with MTLE usually appear normal, but they can sometimes show signs of a dysfunction in certain brain regions. The spike-like activities that appear in the EEG of patients with MTLE usually originate from the deep part of the brain dealing with memory and emotions–the anterior temporal regions. This is more frequent during the sleepy stage and becomes less frequent during deep sleep. When seizures occur, it starts from the place of memory and emotions (hippocampus) and spreads gradually to the basal part of the brain.
Intracranial recordings, which involve the use of sensors placed directly on or into the brain, have helped improve precision in locating the origin of a seizure. This can often reveal that while MTLE primarily involves the temporal lobes of the brain, the network causing seizures can extend to other parts of the brain. So, it’s crucial to check for other areas that could independently cause seizures.
Treatment Options for Mesial Temporal Lobe Epilepsy
First off, patients with Mesial Temporal Lobe Epilepsy (MTLE) often start treatment with a class of drugs known as antiepileptic drugs (AEDs). Certain medications, such as carbamazepine, oxcarbazepine, levetiracetam, lamotrigine, and topiramate, are effective against the type of seizures caused by MTLE. These can be used individually or together to control seizures effectively. However, MTLE tends to not respond well to these medications, with some patients seeing initial success that later fades, resulting in seizures that are resistant to medication.
When medication doesn’t work, other non-drug methods become crucial for managing MTLE. These options include surgery and neurostimulation (the application of a small electric current to parts of the brain).
There are a variety of surgical options available, including both open surgeries and minimally invasive ones. An often-used surgical treatment for MTLE is called open resectioning, where a part of the brain is removed or destroyed. Some possibilities for this type of surgery include removing the anterior temporal lobe, the anteromedial temporal lobe, or selectively removing the amygdala and hippocampus. In general, surgical resection can free 60-80% of MTLE patients from seizures two years after surgery, but longer-term results are somewhat less promising. However, this type of surgery is considered safe, with minor visual field deficits being the most common neurological side effect.
There are alternatives to traditional open resection, including minimally invasive surgical techniques that have come about due to our better understanding of how epileptic networks operate. The goal is to disrupt these networks with the smallest possible surgical intervention. This has led to the development of stereotactic radiosurgery (SRS), stereotactic radiofrequency thermocoagulation (SRT), laser interstitial thermal therapy (LITT), and MRI-guided focused ultrasound ablation (FUS). SRS uses gamma knife or Cyberknife to deliver radiation to a specific part of the brain, usually showing similar post-operation seizure-free outcomes compared to traditional surgery.
If surgery of any kind is not an option or something the patient prefers not to undertake, neurostimulation could be a treatment possibility. Neurostimulation treatments include vagus nerve stimulation (VNS), responsive neurostimulation (RNS), or deep brain stimulation (DBS). These are usually considered for individuals whose seizures originate from two different places in the brain or in vital areas of the brain. It could also be an option for patients whose seizures have returned after surgery.
Lastly, MTLE patients often deal with cognitive issues, mental health conditions and sociocultural challenges in addition to seizures. As such, a thorough treatment plan for MTLE must also consider these conditions.
What else can Mesial Temporal Lobe Epilepsy be?
The seizures experienced by people suffering from medial temporal lobe epilepsy (MTLE) often mimic the characteristics of other epilepsy types. These include absence seizures, insular seizures, and occipital lobe seizures.
- People with ‘absence seizures’ often have a vacant stare and subtle automatic behaviors which can appear similar to MTLE seizures.
- Seizures that arise from the insula could also present symptoms like an abdomen-related aura or mouth-related automatic behaviors, much like temporal lobe epilepsy (TLE).
- In some cases, people with occipital lobe epilepsy have seizures that quickly advance to the temporal lobes, showing symptoms very similar to TLE.
Beyond these, some other medical problems may also copy the characteristics of temporal lobe seizures. These include panic attacks, tardive dyskinesia (a disorder that involves involuntary movements), excessive daytime sleeping, periodic limb movement disorder, short-term psychotic episodes, and non-epileptic seizures caused by psychological factors.
It is necessary to differentiate these using clinical examinations and diagnostic tools such as video-EEG monitoring, a process that records brain activities.
