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(Stroke. 1999;30:2491-2492.)
© 1999 American Heart Association, Inc.

Letters to the Editor

Determination of Cognitive Hemispheric Lateralization by "Functional" Transcranial Doppler Cross-Validated by Functional MRI

S. Knecht, MD; M. Deppe, PhD E-B. Ringelstein, MD

Department of Neurology, University of Münster, Münster, Germany

Key Words: cerebral blood flow • magnetic resonance imaging • ultrasonography

	Introduction

 
To the Editor:

In their article on functional transcranial Doppler sonography (fTCD), Schmidt et al¹ conclude the fTCD can lateralize higher cognitive functions reliably. They suggest that it may be used in patients in the preoperative evaluation before brain surgery. But because "data to validate fTCD...are still lacking," they caution that fTCD should be cross-checked with well established techniques (presumably the Wada test), particularly with regard to language dominance. Stroke published such a study ("Noninvasive Determination of Hemispheric Language Dominance Using Functional Transcranial Doppler Sonography: A Comparison With the Wada Test")² 1 year ago.

Schmidt et al base their suggestions on group averages. Again, it was this very journal that published a study on the feasibility and reproducibility of single-subject assessment by fTCD.³ A full account of the present state of single-case fTCD analysis has already been published by Deppe et al.⁴

Schmidt et al state that "concordant differences between the female and the male subgroup could be visualized."¹ To us, this sentence is somewhat misleading. Changes in lateralization "concordant" in fMRI and fTCD have a 50% chance of occurring in each sex. The authors provide no statistical evidence for sex differences in their paper. Such differences cannot be established by finding significant (P=0.022) lateralization only in females and not in males, particularly as long as no correction for multiple comparisons (eg, Bonferroni) was performed. Even then, they found significant sex differences of cerebral blood flow velocity within neither the left nor the right middle cerebral arteries (figure . . . [Full Text of this Article]

Peter Schmidt, MD¹ ; Timo Krings, MD^{1 2} ; Klaus Willmes, PhD^{2 3} Armin Thron, MD^{1 2}

¹Department of Neuroradiology, ²Interdisciplinary Center for Clinical Research–Central, Nervous System, ³Division of Neuropsychology of the Department of Neurology, University Hospital of the RWTH, Aachen, Germany