Abstracts

Rationale: The standard Wada procedure, which relies heavily on the presentation of visual items, is problematic when a surgical candidate has significant visual impairment/blindness (VI/B). There is no generally accepted approach to modification of the Wada in such cases. We present a model that utilizes auditory and tactile items that are relatively inexpensive and readily available. Confirmation of intact hearing and screening for intact stereognosis (the ability to name objects only by touch) are recommended prior to this Wada procedure. Methods: Case study of a 31-year-old, left-handed, man with medically intractable epilepsy. EEG suggested a left hemisphere focus and semiology suggested a temporal (vs. insular) focus. MRI was normal. Multiple PET studies showed hypometabolism deep within the left superior temporal gyrus. The patient was blind in the left eye. In the right eye, he was legally blind due to congenital glaucoma but retained partial contrast sensitivity in a portion of the temporal visual field sufficient to use adaptive visual devices with difficulty. His visual impairment precluded the use of materials normally used on a standard Wada procedure. Items for the modified Wada included tactile objects from the Fuld Object-Memory Evaluation (which has two 10-item forms), along with a commercially available novelty Sound Machine (Classic version) by NPW that produces 16 unique sound effects.  A total of 8 key items (5 auditory and 3 tactile) were presented on each injection, along with 2 positive foils (items not previously given) and 1 negative foil (a pre-injection baseline item) in each sensory modality. Thus, a total of 14 items (8, 4, 2, respectively) were assessed 10 minutes post-injection in a yes/no format after each injection. Wada memory scores ranged from 0/8 to 8/8.  Neuropsychological memory assessment included immediate and delayed recall of a semantically related list of 12-words (Hopkins’ Verbal Learning Test, Revised) and 8 unrelated word pairs (Verbal Paired Associates, Wechsler Memory Scale, Third Edition). Results: Amytal injection of 125 mg in the left carotid artery produced aphasia, contralateral hemiplegia with preserved consciousness and at 10 minutes the patient correctly identified 7/8 memory items -- consistent with intact memory support in the right hemisphere. Amytal injection of 150 mg in the right carotid artery produced dysarthria, contralateral hemiplegia, with preserved consciousness and at 10 minutes he correctly identified 3/8 memory items – indicative of memory weakness in the left hemisphere.  There were no Wada foil errors.  Neuropsychological assessment showed immediate and delayed verbal recall in the average range for the word list learning, while high average for unrelated word pairs. Conclusions: This modified Wada procedure resulted in a technically satisfactory study with results that were consistent with the patient’s presumed left temporal seizure focus. The procedure provided access to a Wada for a patient who would not otherwise have been able. Although his language dominant hemisphere was shown to be on the left, his average to high average verbal memory scores on neuropsychological testing did not correlate with weak Wada memory performance on the left hemisphere (right injection). Factors such as left-handedness and a history of significant VI/B since birth may have contributed to this discrepancy. Since he has not yet had surgery, we do not know whether the neuropsychological impact of surgery will be consistent with what would be expected based on the Wada. Finally, this modified Wada procedure may not be appropriate for persons with late onset blindness and/or intellectual disability. Funding: None