Temporal Lobe Seizures

Introduction:

Temporal lobe seizures, a subset of epileptic disorders, cast a profound shadow over the lives of those affected. Characterized by recurrent, unpredictable episodes of abnormal electrical activity within the brain's temporal lobes, these seizures can have far-reaching consequences on cognitive, emotional, and physical well-being. In this complex neurological realm, understanding the cardinal features, diagnostic approaches, and management strategies for temporal lobe epilepsy becomes paramount, ultimately shedding light on improved patient care and a better quality of life.

What Is a Temporal Lobe Seizure?

Temporal lobe epilepsy (TLE) is the most prevalent form of partial seizure disorder in adults and often necessitates surgical treatment for those with treatment-resistant epilepsy. TLE patients can be suitable candidates for surgical intervention, particularly when they have a surgically addressable epileptic condition.

TLE can be categorized into two types based on the location of the epileptic focus:

1. Mesial Temporal Lobe Epilepsy (MTLE): This involves the innermost structures of the temporal lobe, including the hippocampus, parahippocampal gyrus, and amygdala. It is the most common type of temporal lobe seizure and is frequently associated with hippocampal sclerosis (HS).

2. Lateral Temporal Lobe Epilepsy (LTLE): The neocortical temporal lobe, LTLE is rare and typically linked to genetic factors or acquired structural and anatomical abnormalities.

Temporal lobe epilepsy encompasses a range of conditions characterized by seizures originating in the temporal lobe. These conditions have diverse underlying causes, including tumors, vascular irregularities, cortical dysplasia, tubers, traumatic injuries, and hippocampal sclerosis. Each of these pathologies likely has a distinct pathologic mechanism linked to the specific nature of the abnormality. Moreover, the functional anatomy of the seizures generated by these pathologies will differ depending on the location of the abnormality within the temporal lobe.

What Are the Clinical Features of Temporal Lobe Seizures?

The clinical features of temporal lobe seizures:

Prodrome:

• Some patients experience warning signs before a seizure that can last minutes to days, including headaches, personality changes, irritability, or anxiety. Often, these signs are noticed by others rather than the patient.

Aura:

• Auras are actually simple partial seizures and often precede complex partial seizures (CPS) that last from seconds to a couple of minutes.

• The type of aura may relate to where the seizure originates in the temporal lobe. These include sensory sensations like stomach sensations, experiential phenomena (feelings of fear), and hallucinations (gustatory and olfactory).

Altered Consciousness:

• Complex partial seizures involve altered consciousness, typically characterized by behavioral arrest and staring that lasts for 30 seconds to a couple of minutes.

• It is important to distinguish impaired awareness from temporary communication or comprehension difficulties while maintaining conscious awareness.

Amnesia:

• Individuals with seizures may not be aware they had a seizure and may not remember events before the seizure.

• The extent of memory loss varies, often resulting from bilateral impairment of hippocampal function.

Automatisms:

• Automatisms are involuntary motor activities that occur alongside altered consciousness during seizures that can be spontaneous or preservative.

• Common automatisms involve actions like fumbling, lip-smacking, or chewing.

• Less common ones include vocalizations, unusual behaviors (crying or laughing), and even leaving behaviors (running during a seizure).

Types of Temporal Lobe Seizures:

• Temporal lobe seizures can be simple partial, complex partial, or secondarily generalized.

• Specific features of these seizures provide insights into the origin and localization within the temporal lobe.

How Are Temporal Lobe Seizures Assessed?

Neuroimaging and EEG play crucial roles in evaluating individuals suspected of having temporal lobe epilepsy. Since seizures are intermittent and infrequent for most epilepsy patients, conducting diagnostic assessments between seizures is essential.

EEG (Electroencephalography):

• EEG should be performed for all suspected temporal lobe epilepsy cases.

• It helps pinpoint the location of the epileptic networks.

• A diagnostic ictal EEG recording typically shows a rhythmic five to seven-hertz theta-wave frequency with peak recordings in sphenoidal and basal temporal electrodes on the same side as the epileptic focus.

• Interictal EEG may reveal spike-and-wave or sharp and slow complexes, often in the anterior temporal region.

• Differentiating between mesial temporal lobe epilepsy (MTLE) and lateral temporal lobe epilepsy (LTLE) through EEG can be challenging as the waveforms are similar.

• In cases of normal initial EEG results, sleep deprivation, and video EEG telemetry may aid in diagnosis, intracranial electrodes could be considered if there is discordance between scalp EEG and other clinical data.

Neuroimaging:

• Neuroimaging is crucial to identify structural anomalies causing temporal lobe seizures, such as vascular malformations, tumors, and hippocampal sclerosis.

• Computed tomography (CT) scans are commonly used but have limited sensitivity compared to MRI (Magnetic Resonance Imaging), which is the preferred method.

• MRI is vital for pre-surgical assessment, with hippocampal sclerosis being a common finding.

• MRI can reveal reduced hippocampal volume and increased signal intensity on T2 imaging.

• T1 imaging provides detailed neuroanatomical information.

• Approximately 57 percent of epileptogenic lesions are missed on standard MRI, making referral to specialized epileptic clinics advisable for access to functional neuroimaging modalities.

• In inconclusive cases, functional imaging with positron emission tomography (PET) or magnetic resonance spectroscopy (MRS) may be considered.

Pre-surgical Evaluation:

• For individuals considering surgery, precise localization of the epileptic focus while preserving unaffected areas is crucial.

• In cases where MRI doesn’t reveal epileptic foci, additional imaging may be needed.

• PET scans can identify epileptogenic zones interictally, independently, or in conjunction with CT or MRI.

• SPECT scanning is useful in identifying epileptic foci in most cases, particularly during seizures.

• Magnetic rncephalography (MEG) measures magnetic fields generated by interictal spikes and can be used with MRI for three-dimensional magnetic source imaging.

• The intra-carotid amobarbital test (WADA test) traditionally assesses memory centers in temporal lobes but is invasive. Functional MRI has shown promise as a less invasive alternative for language center assessment and postsurgical outcome evaluation. Limited evidence supports its effectiveness compared to the WADA test.

What Is the Treatment and Management of Temporal Lobe Epilepsy?

Treatment and management of temporal lobe epilepsy are crucial for improving a patient’s quality of life and reducing the cumulative time spent in seizures, which can lead to neurocognitive decline. This includes

Pharmacological Interventions:

• Initial management upon diagnosis usually involves antiepileptic drugs (AEDs).

• Older AEDs like Phenytoin, Valproate, Carbamazepine, and Phenobarbital are equally effective as newer AEDs but may have more adverse effects.

• Women of childbearing should consider the potential teratogenicity of AEDs in the first trimester.

• About one-third of patients may not achieve seizure resolution with AEDs.

Refractory Epilepsy:

• For individuals who do not respond to AEDs, a definition of refractory epilepsy is based on various factors, including seizure frequency, severity, the number of AED failures, adverse effects, and impact on daily life.

• Surgical options may be considered for refractory cases, providing up to an 80 percent remission rate, especially in cases of hippocampal sclerosis.

Surgical Interventions:

• Two common surgical procedures are anterior temporal lobectomy (ATL) and selective amygdalohippocampectomy (AHP).

• A meta-analysis shows no significant difference in one-year seizure freedom between ATL and AHP but a significant improvement compared to AEDs.

• ATL techniques involve the anterior temporal lobe, while AHP focuses on preserving lateral temporal lobe function.

• Less invasive approaches, such as stereotactic radiosurgery and laser ablation, are considered for challenging or high-risk cases.

• Stereotactic radiosurgery has a latency period for maximum therapeutic benefits and may not be suitable for certain lesions.

• Stereotactic laser ablation has shown promise in achieving therapeutic outcomes.

Alternative Options:

• Neurostimulation options like vagus nerve stimulation (VNS) and responsive neurostimulation (RNS) are available.

• Deep brain stimulation is still undergoing evaluation and is not FDA-approved for refractory epilepsy in the United States.

• Ketogenic dieting may be considered to reduce seizure frequency.

Conclusion:

Temporal lobe seizure is proof of the intricate interplay between neuroscience and clinical medicine. These seizures, with myriad presentations and challenges, have prompted the development of a multidimensional approach to diagnosis and management. From the meticulous analysis of electroencephalograms to the evolving landscape of surgical interventions, the quest for effective solutions continues.