RESPONSE

Abstract

To the Editor: We thank Dr. Derakhshan for his interesting general remarks on hemispheric dominance. It is an exciting speculation whether the patient described in our article 1 might be a “fake-hander.” However, the distinction between neural and behavioral handedness seems quite theoretical and not appropriate in the evaluation of patients before surgical intervention. It has been known for a long time that the strong coincidence between right-handedness and left hemisphere language dominance in normal subjects is much less consistent in patients with epilepsy 2. Neither neural nor behavioral handedness is suitable to predict the cerebral language organization in patients with epilepsy. Therefore it is the aim of the procedures applied in the presurgical evaluation [Wada test, functional magnetic resonance imaging (fMRI), cortical stimulation] not to analyze the laterality of movement control (handedness and speech), but to determine whether a surgical resection in a given patient is likely to induce a deficit (e.g., language, motor, memory). For this purpose we—and as far as we know, all major epilepsy centers—indeed do rely on the Wada test. In accordance with Loring et al. 3, we believe that the Wada test is the least ambiguous method to test for hemispheric language dominance. Our reliance is not restrained by the articles cited by Dr. Derakhshan. The variability of the results of the studies by Risse et al. 4 and by Mamelak et al. 5 simply reflects differences between the examined patient populations. The results of Risse et al. 4 represent the generally accepted proportion of the different types of cerebral language representation in a large sample of epilepsy patients (82% left dominant, 18% atypical). On the contrary, the observations by Mamelak et al. 5 resulted from a patient group with severe bilateral epilepsies in whom a callosotomy was performed. It is not surprising at all that atypical (i.e., non–left-dominant language representation) is highly overrepresented in this selected group. From our point of view, it is not dubious to speculate about the reasons for the right-hemisphere language dominance in our patient. Strong evidence from the literature indicates that atypical language dominance and non–right-handedness is frequently observed in patients with early left hemisphere brain lesions or early onset of seizures originating from the left hemisphere 1, 3, 5. Therefore it remains open whether the right-hemisphere language dominance in our patient was primary or a consequence of his left-hemisphere injury, representing functional plasticity. The Wada test and cortical stimulation cannot be completely replaced in the presurgical evaluation of patients with epilepsy. In our opinion, determination of the “neural handedness” is completely useless in this context. fMRI will help to reduce the number of patients in whom invasive procedures are mandatory 6.