Clinical Presentation, Electroencephalography (EEG), and MRI of Mesial Temporal Lobe Epilepsy (MTLE)

Mesial temporal lobe epilepsy (MTLE) is one of the most common, in fact, the most common syndrome associated with focal seizures and cognitive impairment. It is diagnosed based on typical clinical presentation and EEG findings. Radiological features could help in diagnosis but is not part of the definition. The international leagues against epilepsy (ILAE) did not include this terminology into its classification but rather used a more general term; temporal lobe epilepsy. Mesial temporal sclerosis (MTS) is considered a pathological substrate of MTLE. MTLE is interesting and important to know because it is often intractable to medical treatment and treatable by surgical approach. [ref1][ref2]

The clinical presentation [ref1][ref2][ref3]

The presentation is variable but can be divided into 2 forms, those that felt by the patients; aura, and one that we can see; observable neurological manifestation.

During the onset of seizure, one could feel an odd raising sensation from the abdomen. Less commonly, one also could experience a sense of fear, déjá vu, jamais vu, olfactory hallucinations, and sometimes depersonalization. Some may also unable to describe the aura, probably as a result of complex partial seizure which associated with amnesia.

In observable neurological manifestation include motor arrest, staring and automatism. Others include unilateral posturing, mpostictal disorientation and postictal dysphasia. Literatures has described that unilateral dystonic posture of an arm as a localizing features is highly accurate when combined with contralateral hand’s automatism.

Electroencephalography (EEG) of MTLE. [ref1][ref4]

EEG used in helping the diagnosis of MTLE can be divided into interictal and ictal state. The characteristic EEG findings during interictal state is anterior temporal sharp waves, spikes and followed by slow waves. This are present in up to 94% of the patients. During ictal state, the scalp EEG will shows unilateral 5-7 Hz rhythmic discharges that appears within the first 30 seconds of the first objective or subjective clinical sign and symptoms of a seizure; in anterior-inferior temporal scalp EEG. This characteristic rhythm occurs in about 90% of patients with MTLE and has 95% specificity for lateralizing the seizure.

interictal eeg of mesial temporal lobe epilepsy

Image above shows the EEG finding during interictal state of MTLE; a typical epileptiform abnormality with spike or sharp wave with negative polarity and followed by a slow wave. Image obtained from [ref4].

ictal eeg of mesial temporal lobe epilepsy

Image above shows the EEG finding in ictal state of MTLE; a lateralized rhythmic 5-7 Hz sharp activity appeared within first 30 seconds of clinical sign and symptoms. Image obtained from [ref4].

MRI of MTLE
Commonly used is structural MRI in helping the diagnosis along side with FLAIR sequences to enhance the images. The abnormalities able to be detected by naked eyes on structural MRI can be divided into primary and secondary abnormalities. Primary abnormalities includes unilateral hippocampal atrophy and hyperintensity of medial temporal or hippocampas. Secondary abnormalities includes unilateral fornix column, mamillary body, and amygdala atrophy. These were said to be secondary because of the indirect consequences of hippocampal atrophy. [ref5][ref6]

mesial temporal sclerosis

Image above shows the hyperintensity of left hippocampus on MRI FLAIR sequence. This is an image of left mesial temporal sclerosis. Image obtained from [ref5]

bilateral mesial temporal sclerosis

Image above shows a hyperintensities of right hippocampus on MRI FLAIR sequence, compared with the left (black arrows) which is normal. Image obtained from [ref2].

Hippocampal atrophy detected by MRI volumetry has 75% sensitivity, and 64% specificity for ipsilateral medial temporal lobe seizure [ref7]. It is also stated that there is a relationship between between scalp EEG lateralization and side of hippocampal atrophy detected by MRI in patients with MTLE [ref8]. In another study, MRI has were able to lateralised the lesion by a number of 72% of intractable epilepsy (including MTLE) with the pathologic diagnosis as the standard of reference [ref9].

References
1. Burneo, Jorge G; Demaerschalk, Bart M.; Jenkins, Mary E. eds. Neurology: an evidence-based approach. New York, NY: Springer; 2012:161-174
2. Stephen L. Hausser. Ed. Harrison’s neurology in clinical medicine. 2nd edition. McGraw Hill. New York, NY. 2010
3. Charles Clarke et. al. Ed. Neurology A Queen Square textbook. 1st edition. Blackwell Publishing Ltd. 2009.
4. Manouchehr Javidan. Electroencephalography in Mesial Temporal Lobe Epilepsy: A Review. Hindawi Publishing Corporation Epilepsy Research and Treatment. Volume 2012, Article ID 637430, 17 pages doi:10.1155/2012/637430.
5. Radhika G. Gupta. Magnetic resonance imaging of temporal lobe epilepsy. Supplement to Radiology. 2010. pg 22
6. D. H. Jogi and M. Patel. Case Report Mesial temporal sclerosis. SA Journal of Radiology. 2005; pg 25-27
7. Susan S. Spencer and Dennis D. Spencer. Diagnosis of medial temporal lobe seizure onset: Relative specificity and sensitivity of quantitative MRI. Neurology October 1, 1993 vol. 43 no. 10, pg 2117.
8. Fernando Cendes et al. Is Ictal Recording Mandatory in Temporal Lobe Epilepsy? Not When the Interictal Electroencephalogram and Hippocampal Atrophy Coincide. Arch Neurol. 2000;57(4):497-500.
9. Hyung J. Wong et al. Comparison of MR Imaging with PET and Ictal SPECT in 118 Patients with Intractable Epilepsy. AJNR Am J Neuroradiol. 1999; 20:593–599

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