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Changes in cortical excitability differentiate generalized and focal epilepsy

Authors

  • Radwa A. B. Badawy MBBCh, MSc,

    1. Department of Neurology, Austin Health, Heidelberg, Australia
    2. Epilepsy Research Centre, Department of Medicine, University of Melbourne, Heidelberg West, Victoria, Australia
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  • Josie M. Curatolo MApplSci,

    1. Department of Neurology, Austin Health, Heidelberg, Australia
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  • Mark Newton MD, FRACP,

    1. Department of Neurology, Austin Health, Heidelberg, Australia
    2. Epilepsy Research Centre, Department of Medicine, University of Melbourne, Heidelberg West, Victoria, Australia
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  • Samuel F. Berkovic MD, FRACP,

    1. Department of Neurology, Austin Health, Heidelberg, Australia
    2. Epilepsy Research Centre, Department of Medicine, University of Melbourne, Heidelberg West, Victoria, Australia
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  • Richard A. L. Macdonell MD, FRACP

    Corresponding author
    1. Department of Neurology, Austin Health, Heidelberg, Australia
    2. Epilepsy Research Centre, Department of Medicine, University of Melbourne, Heidelberg West, Victoria, Australia
    • Department of Neurology, Austin Health, Studley Road, Heidelberg, Victoria 3084, Australia
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Abstract

Objective

Different pathophysiological mechanisms related to the balance of cortical excitatory and inhibitory influences may underlie focal and generalized epilepsies. We used transcranial magnetic stimulation to search for interictal excitability differences between patients with idiopathic generalized epilepsy (IGE) and focal epilepsy.

Methods

Sixty-two drug-naive patients with newly diagnosed epilepsy (35 IGE, 27 focal epilepsy) were studied. In the latter group, the seizure focus was not located in the motor cortex. Motor threshold at rest, cortical silent period threshold, recovery curve analysis using paired-pulse stimulation at a number of interstimulus intervals), and cortical silent period were determined. Results were compared with those of 29 control subjects.

Results

Hyperexcitability was noted in the recovery curves at a number of interstimulus intervals in both hemispheres in patients with IGE and in the hemisphere ipsilateral to the seizure focus in those with focal epilepsy compared with control subjects and the contralateral hemisphere in focal epilepsy. Motor threshold and cortical silent period threshold were higher in the ipsilateral hemisphere in focal epilepsy compared with the contralateral hemisphere. No other intragroup or intergroup differences were found in the other measures.

Interpretation

The disturbance of cortical excitatory/inhibitory function was found to be bilateral in IGE, whereas in focal epilepsy it spread beyond the epileptic focus but remained lateralized. This finding confirms that there are differences in cortical pathophysiology comparing the two major types of epilepsy. Ann Neurol 2007

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