A letter published in the September issue (“Reduced Hippocampal and Amygdalar Volume in Dissociative Identity Disorder: Not Such Clear Evidence” Am J Psychiatry 2006; 163:1643) referenced an editorial by Dr. David Spiegel, but the Journal did not invite Dr. Spiegel to respond to the points raised by the letter writers. His response appears below.
To the Editor: Tom Smeets, M.Sc., et al. (1) assert that age differences must account for findings made in a study by Eric Vermetten, M.D., Ph.D., et al. of smaller hippocampal and amygdalar volume in patients with dissociative disorders (2). Smeets et al. assume that they must be correct despite—among other things—the fact that, in the Vermetten et al. study, right amygdalar volume was smaller in the dissociative disorder group even when age was controlled (3). Dr. Vermetten et al. point out that age-related reductions in hippocampal volume occur over age 50 and more clearly in men, who were not the subject of their study. Smeets et al. then assert, surprisingly, that “there is good evidence that suffering from a major psychiatric disorder may lead to accelerated aging in middle-aged people.” Presumably, they make this argument to indicate that this rapid aging is associated with reduced hippocampal and amygdalar volume and could therefore “account” for the findings made by Dr. Vermetten et al. But that is just the point of their study—that dissociative identity disorder, a major psychiatric illness, is associated with smaller hippocampal and amygdalar volume (4). The comparison subjects did not have major psychiatric disorders, so this criticism is reduced to one of specificity at most—perhaps other psychiatric disorders are also associated with reduced hippocampal and amygdalar volume. Thus the observation by Dr. Vermetten et al. and my comment on it (5) stand, and as we all age, we need to work harder to remember that the volume reduction is real and that the existence of some putative reasons for it does not invalidate others.