Case Study

A 38 year-old left-handed female developed drug-resistant focal epilepsy at 33 years of age without risk factors. Weekly seizures began with déjà vu and evolved to a stare and impaired consciousness without lateralizing features. An MRI of the brain demonstrated a cavernous vascular malformation in the posterior 2nd mid-temporal gyrus. An FDG PET was normal. In-patient video-EEG demonstrated right > left temporal sharp waves with a 90:10% ratio (maximum at T2/T1 and F8/F7), and focal seizures with a right regional temporal rhythmic ictal theta onset. Neuropsychological evaluation had deficits in both verbal and performance memory function. Wada testing using 5 mg of methohexital lateralized language function. A memory asymmetry had 5/8 targets identified on right injection, and 7/8 on left injection among 16 object distracters. An fMRI lateralized language function to the left hemisphere (see answer).

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Figure: (A) EEG with right hemispheric slowing on injection of 3 mg of Brevital® and (B) fMRI demonstrating left superior temporal activation during memory encoding using an auditory semantic decision task (courtesy of V Gupta MD). EEG parameters include a bipolar montage, sensitivity of 7 uv/mm, and filters of 1-70 Hz.

How can Wada testing work with functional MRI?

Anterior temporal lobectomy (ATL) is an effective treatment in patients with drug-resistant temporal lobe epilepsy. The Wada test was originally developed to assess the risk of language decline prior to craniotomy and was later applied to predict global amnesia following ATL. Up to ½ of patients undergoing left ATL for drug-resistant focal seizures show a post-operative decline in language or verbal memory function. Language lateralization appears to be a better predictor of verbal memory outcome than Wada memory testing (1). fMRI is non-invasive and may often substitute for the Wada test when lateralizing language. Some authors question the reliability and validity of the Wada test to predict memory outcome. Hence, over time the Wada test has become less often utilized to complement non-invasive studies. In one study only 12% of center used Wada in every TLE candidate (2), and it may be best used in those with atypical language or with significant bitemporal dysfunction. Recent fMRI studies demonstrate the pre-operative predictive value of fMRI for post-operative memory changes (1). Our patient received a right ATL after invasive EEG without language or memory deficits.

References

  1. Binder JR. Functional MRI is a valid noninvasive alternative to Wada testing. Epilepsy & Behavior 2011;20:214-220.
  2. Baxendale S. The role of the Wada test in the surgical treatment of temporal lobe epilepsy: An international study. Epilepsia 2008;49(4):715-720.
Authored By: 
William O. Tatum DO
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Authored Date: 
03/2011