Neurology -- Correspondence for Stroup et al., 60 (8) 1266-1273

Correspondence published:

Reply to Jokeit: John Langfitt, PhD, Elizabeth Stroup, PhD (29 September 2003)

Predicting verbal memory decline following anterior temporal lobectomy (ATL): Hennric Jokeit (29 September 2003)

Reply to Jokeit 29 September 2003

John Langfitt, PhD,
Associate Professor, Depts of Neurology & Psychiatry
University of Rochester, 601 Elmwood Ave., Box 673, Rochester, NY 14642,
Elizabeth Stroup, PhD
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Re: Reply to Jokeit

John_langfitt{at}urmc.rochester.edu John Langfitt, PhD, et al.

We appreciate Dr. Jokeit’s comments and the opportunity to clarify the two important issues that he raises.
Dr. Jokeit infers that our data suggest that a bilateral IAP is an unnecessary risk for patients considered for anterior temporal lobectomy. We did not specifically address this because it cannot be resolved with our data. We could only show that ipsilateral injection scores at the higher end of the range are not predictive of verbal memory decline. Our study could not address the predictive value of scores across the entire range. As is common practice elsewhere, our patients with low ipsilateral injection scores (i.e. IAP ‘failures’) were generally excluded from surgery due to post-operative amnesia--a detail inadvertently omitted from our Methods. As we discussed, this practice keeps the IAP from being a true test of the functional reserve and functional adequacy hypotheses, since the range of contralateral injection scores is unrestricted. Had patients with low ipsilateral injection scores been included (as may be the case in the studies that Dr. Jokeit cites), these scores may have been a stronger predictor of memory decline. If so, this would indeed support the utility of an ipsilateral IAP.
In addition, Dr. Jokeit suggests that separate models and outcome variables are appropriate for predicting outcome following dominant and non-dominant resections. Indeed, dominant and non-dominant resections can have qualitatively different effects on cognition. Studies would thus be worthwhile that use cognitive measures similarly sensitive to non-dominant temporal lobe functioning. However, the more practical, clinical aim of our study was to predict individual verbal memory decline in all ATL patients, because of the importance of verbal memory to postoperative functioning and the known (albeit lower) incidence of verbal memory decline after non-dominant ATL 4.
To test Dr. Jokeit’s suggestion that the current model performed differently in the two groups, we reanalyzed our data, but included interaction terms to see whether the variables predicted different amounts of variance in the two groups. None of the interactions approached significance ( p > .40 for all variables). Admittedly, power is limited to detect such interactions if they truly exist, given the sample size. However, in separate analyses of the two resection groups, there were no notable differences between the parameter estimates. This suggests that the prediction model functions similarly for both groups.
References
4) Chelune GJ, Naugle R, Luders H. Individual change following epilepsy surgery: practice effects and baserate information. Neuropsychology 1993;7:41-52.

Predicting verbal memory decline following anterior temporal lobectomy (ATL) 29 September 2003

Hennric Jokeit,
Swiss Epilepsy Center, Zurich, Switzerland
Swiss Epilepsy Center, 8008 Zürich, Bleulerstrasse 60
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Re: Predicting verbal memory decline following anterior temporal lobectomy (ATL)

h.jokeit{at}swissepi.ch Hennric Jokeit

I read with interest the article by Stroup et al. [1] on the prediction of verbal memory decline following anterior temporal lobectomy of 132 patients with refractory temporal lobe epilepsy (TLE). Based on the results of a multiple logistic regression analysis, the authors report an increased risk of postsurgical memory deficit for: a resection in the dominant hemisphere; MRI findings other than exclusively unilateral mesial temporal sclerosis; intact preoperative verbal memory function; and intact intracarotid amobarbital procedure (IAP) memory performance following injection contralateral to the seizure focus. Furthermore, it is shown that the data of ipsilateral IAP memory testing did not provide additional information. From the latter results it can be concluded that a bilateral IAP is an unnecessary risk for patients considered for anterior temporal lobectomy. The claim that an ipsilateral IAP is sufficient for prediction of memory decline in both patients with dominant and non-dominant-sided TLE is unconfirmed. This study estimates that the base rate of postoperative memory deficits in patients with dominant-sided TLE is 46 % and in patients with non-dominant-sided TLE 11 %. Seventy-four patients of the sample underwent non-dominant surgery. Thus, the subgroup at highest risk for memory deficits is a minority in the sample. It is well known that dominant and non-dominant temporal lobe lesions induce qualitatively different deficits in memory and cognition. It is also known that the used verbal memory tests (Logical Memory, WMS-R; CVLT) are insensitive for right temporal lobe lesions as well as ATL. Studies that exclusively considered patients with left-dominant-sided resections provided strong evidence that the ipsilateral IAP is of high prognostic value showing whether the right temporal lobe provides sufficient memory resources for compensation.[2,3] I assume that the forecast of memory decline following dominant and non-dominant ATL needs different models as well as variables that consider the fundamental differences of left and right brains. There is no need to fit dominant and non-dominant resection effects within one and the same model with a risk of a bias.
References
1. Stroup E, Langfitt J, Berg M, McDermott M, Pilcher W, Como P. Predicting verbal memory decline following anterior temporal lobectomy (ATL). Neurology. 2003;60:1266-1273.
2. Bell BD, Davies KG, Haltiner AM, Walters GL. Intracarotid amobarbital procedure and prediction of postoperative memory in patients with left temporal lobe epilepsy and hippocampal sclerosis. Epilepsia. 2000; 41:992-997.
3. Jokeit H, Ebner A, Holthausen H, et al. Individual prediction of change in delayed recall of prose passages after left-sided anterior temporal lobectomy. Neurology. 1997; 49:481-487.