| The current accepted method for determining language laterality is the intracarotid amytal (Wada) test. Various patient characteristics have been investigated to examine if they contribute to language lateralization. These include side of seizure focus, site of focus, age of onset, handedness, family history of handedness, age of onset, and gender. Findings have varied across studies. Findings have varied across studies, and most have investigated these factors individually or have used small sample sizes.; This study used data from 426 patients who had a Wada test at the University of California - San Francisco and for whom there was adequate data from each injection to classify the patient's language laterality, and for whom complete data was available for the independent variables side of focus, site of focus (anterior temporal, posterior temporal, frontal, parietal), handedness, family history of handedness, age of onset, sex, and etiology (epilepsy, tumor, AVM). The dependent variable, language laterality, was classified using the "Walker" Method (Left Only, Left > Right, Left = Right, Right > Left or Right Only) based on the pattern of disrupted or intact expressive and receptive speech during the amytal injection. The language laterality data was also reclassified into three categories of language representation (Left, Bilateral or Right) using the best estimate of two alternative categorization strategies. This provided three distributions to test the predictive ability of patient characteristics on language laterality.; Stepwise multiple regression was used to determine the amount of variance accounted for in language laterality by predictor variables. Of the 12 possible predictor variables, only 4 were found to significantly account for variance in language laterality. These variables, and the amount of variance accounted for, were: Handedness (13.4%), Side of focus (3.5%), Posterior Temporal site (1.8%), and Age of Onset (0.9%), for a total of 19.7% of the variance. Re-categorization of the language laterality results using two additional methods of categorization yielded the same sequence of variables, though the total amount of variance accounted for was less, at 17.5% and 15%.; Based on these findings, it seems difficult to predict language representation, and reasonable to continue to perform Wada tests. |
