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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.
Mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) is the most common type of focal 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).
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 5).
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 6).
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.
Complications
Drug resistant epilepsy is a major clinical challenge affecting about 30% of temporal lobe epilepsy (TLE) patients.
The reasons for failure of surgical treatment for mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS) remain unclear.
Treatment
Mesial temporal lobe epilepsy treatment.
Outcome
After surgery for intractable mesiotemporal lobe epilepsy (mTLE) seizures recur in 30-40%. One predictor for seizure recurrence is the distribution of seizure onset and interictal epileptiform discharges (IED).
Preoperative bilateral ictal foci are a negative predictor for seizure outcome. Contrarily, IED exceeding the affected temporal lobe in the ipsilateral hemisphere or even bilateral IED had favorable seizure outcome if seizure onset is strictly limited to the affected temporal lobe. Reoperation for seizure persistence constitutes a promising therapeutic option 7).
The extent of pre-surgical perifocal PET abnormalities, the extent of their resection, and the extent of non-resected abnormalities were not useful predictors of individual freedom from seizures in patients with TLE 8).
Case series
see Mesial temporal lobe epilepsy case series.
References
