Mesial temporal lobe epilepsy
Temporal lobe epilepsy (TLE) is a chronic neurological condition characterized by recurrent seizures (epilepsy) which originate in the temporal lobe of the brain with progressive neurological disabilities, including cognitive deficit, anxiety and depression.
The seizures involve sensory changes, for example smelling an unusual odour that is not there, and disturbance of memory.
Epidemiology
Temporal lobe epilepsy (TLE) is considered to be the most common form of epilepsy, and it has been seen that most patients are refractory to antiepileptic drugs.
Drug resistant epilepsy is a major clinical challenge affecting about 30% of temporal lobe epilepsy (TLE) patients.
Mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) is the most common type of focal epilepsy.
Classification
Non-lesional mesial temporal lobe epilepsy
Etiology
see Temporal lobe epilepsy etiology.
Pathophysiology
In order to understand the pathophysiology of temporal lobe epilepsy (TLE), and thus to develop new pharmacological treatments, in vivo animal models that present features similar to those seen in TLE patients have been developed during the last four decades. Some of these models are based on the systemic administration of chemoconvulsants to induce an initial precipitating injury (status epilepticus) that is followed by the appearance of recurrent seizures originating from limbic structures.
Kainic acid and pilocarpine models, have been widely employed in basic epilepsy research. Their behavioral, electroencephalographic and neuropathologic features and response of these models to antiepileptic drugs and the impact they might have in developing new treatments are explained in the work of Lévesque et al. 1).
The transition to the ictal stage is accompanied by increasing global synchronization and a more ordered spectral content of the signals, indicated by lower spectral entropy. The interictal connectivity imbalance (lower ipsilateral connectivity) is sustained during the seizure, irrespective of any appreciable imbalance in the spectral entropy of the mesial recordings 2).
Clinical features
Recurrent seizures (epilepsy) which originate in the temporal lobe of the brain with progressive neurological disabilities, including cognitive deficit, anxiety and depression.
The seizures involve sensory changes, for example smelling an unusual odour that is not there, and disturbance of memory.
Olfactory function was significantly impaired in patients with MTLE compared with healthy controls in all domains, namely threshold, discrimination, and identification. In addition, the olfactory bulb volume was smaller in patients with olfactory dysfunction 3).
Earlier tachycardia for seizures originating from the right versus left hemisphere in a patient with bilateral mesial temporal lobe epilepsy 4).
A strong association of this ailment has been established with psychiatric comorbidities, primarily mood and anxiety disorders. The side of epileptogenic may contribute to depressive and anxiety symptoms; thus, in a study, Radaelli et al. performed a systematic review to evaluate the prevalence of depression in TLE in surgical patients. The literature search was performed using PubMed/Medline, Web of Science, and PsycNet to gather data from inception until January 2019. The search strategy was related to TLE, depressive disorder, and anxiety. After reading full texts, 14 articles meeting the inclusion criteria were screened. The main method utilized for psychiatric diagnosis was Diagnostic and Statistical Manual of Structured Clinical Interview for DSM Disorders. However, most studies failed to perform the neuropsychological evaluation. For those with lateralization of epilepsy, focus mostly occurred in the left hemisphere. For individual depressive diagnosis, 9 studies were evaluated, and 5 for anxiety. Therefore, from the data analyzed in both situations, no diagnosis was representative in preoperative and postoperative cases. In order to estimate the efficacy of surgery in the psychiatry episodes and its relation to seizure control, the risk of depression and anxiety symptoms in epileptic patients need to be determined before surgical procedures. Rigorous preoperative and postoperative evaluation is essential for psychiatry conditions in patients with refractory epilepsy candidates for surgery 5).
Diagnosis
A pilot study demonstrates that seizures in mesial temporal and temporal-plus epilepsies (i.e., temporoperisylvian) can be detected reliably in the anterior thalamic nucleus (ATN). Further studies are needed to validate these findings 6).
Fractional anisotropy asymmetry (FAA) values can be potentially used to identify the seizures of origin of TLE and to help understand the relationship between fiber tracts with the side of seizure origin of TLE 7).
The area of predominant perifocal 18F positron emission tomography hypometabolism and reduced [11C]flumazenil (11C-FMZ) -binding on PET scans is currently considered to contain the epileptogenic zone and corresponds anatomically to the area localizing epileptogenicity in patients with temporal lobe epilepsy (TLE).
Differential diagnosis
Mesial temporal lobe epilepsy differential diagnosis.
Treatment
Mesial temporal lobe epilepsy treatment.
Outcome
Mesial temporal lobe epilepsy outcome.
Case series
see Mesial temporal lobe epilepsy case series.