Stressing About Posttraumatic Stress Disorder

Abstract

To the Editor .— We are writing to you about a recent article that appeared in Pediatrics .1 The authors of this very interesting article claimed that posttraumatic stress disorder (PTSD) “symptoms and cortisol levels at baseline are associated with changes in hippocampal volume over an ensuing 12- to 18-month interval” after a stressful life event. However, we believe that this strong claim is not supported by the data the authors presented. The first problem is that the methods the authors used to measure hippocampal volume are of low precision. In all studies that use MRI to measure brain volume, experimental variance can be introduced during data acquisition (eg, patient motion, changes in scanner hardware or software, scanner field variation) and during data analysis (eg, partial-volume problems, voxel misclassification, manual delineation error).2 Among the 15 children who they evaluated, the authors acknowledged (in line 3 of “Results”) that there was 1 child who showed an increase in right hippocampal volume that amounted to a full SD, or ∼15%. This child was excluded from additional evaluation. However, the existence of 1 outlier this extreme suggests that the method of measuring hippocampal volume was relatively imprecise. This inference is consistent with the fact that the authors measured interrater reliability but did not report the results. If we hypothesize that the volume-measurement methods used were imprecise and that hippocampal volume of these subjects did not actually change over the time interval studied, what results would have been obtained? We would expect that hippocampal volume change scores would have fluctuated randomly and would not have been significantly different from 0. This is precisely the outcome shown in Table 1, in …