Hippocampal and Amygdalar Volumes in Dissociative Identity Disorder

Eric Vermetten, M.D., Ph.D. Christian Schmahl, M.D.
Sanneke Lindner, M.Sc. Richard J. Loewenstein, M.D. J. Douglas Bremner, M.D. (Am J Psychiatry 2006; 163:1–8)

Objective: Smaller hippocampal volume has been reported in several stress-related psychiatric disorders, including posttraumatic stress disorder (PTSD), borderline personality disorder with early abuse, and depression with early abuse.

Patients with borderline personality disorder and early abuse have also been found to have smaller amygdalar volume. The authors examined hippocampal and amygdalar volumes in patients with dissociative identity disorder, a disorder that has been associated with a history of severe childhood trauma....

Results: Hippocampal volume was 19.2% smaller and amygdalar volume was 31.6% smaller in the patients with dissociative identity disorder, compared to the healthy subjects. The ratio of hippocampal volume to amygdalar volume was significantly different between groups.

Conclusions: The findings are consistent with the presence of smaller hippocampal and amygdalar volumes in patients with dissociative identity disorder, compared with healthy subjects....

In clinical studies, most patients with dissociative identity disorder have also been found to meet the DSM-IV-TR criteria for posttraumatic stress disorder (PTSD). In epidemiological studies of the general population,
the prevalence of dissociative identity disorder has been found to range from 1% to 3%.

Numerous studies have shown an association between a dissociative identity disorder diagnosis and an antecedent history of childhood trauma, usually multiple, sustained forms of maltreatment beginning in early childhood....

Magnetic resonance imaging (MRI) studies have shown that adults with PTSD related to combat or to childhood physical/sexual abuse have smaller hippocampal size, relative to healthy comparison subjects or to comparison subjects who experienced trauma but did not develop PTSD.

Borderline personality disorder is also commonly associated with exposure to childhood trauma. Patients with borderline personality disorder and a history of early abuse have been found to have smaller hippocampal and amygdalar volumes, compared to healthy subjects. Smaller hippocampal volume has been found in patients with major depressive disorder and a history of early childhood trauma, compared to major depressive disorder patients without early life trauma. A consistent finding of these studies is smaller hippocampal volume in patients with a history of exposure to traumatic stress and an accompanying
stress-related psychiatric disorder....

All patients with dissociative identity disorder in this study also had a diagnosis of PTSD according to the DSMIV-TR criteria and the Clinician-Administered PTSD Scale....

Electrical stimulation of the hippocampus and adjacent regions in patients with epilepsy resulted in a number of dissociative-like symptoms, including feelings of déjà vu, depersonalization, derealization, and memory alterations. Administration of ketamine, an antagonist of N-methyl-D-aspartic acid (NMDA) receptors, which are highly concentrated in the hippocampus, resulted in dissociative symptoms in healthy subjects, including feelings of being out of body and of time standing still, perceptions of body distortions, and amnesia. On the basis of these findings, we have hypothesized that stress, acting through NMDA receptors in the hippocampus, may mediate symptoms of dissociation....

Clinical studies have found comorbid PTSD or a lifetime history of PTSD in 80%–100% of dissociative identity disorder patients. Davidson and Foa, in their summary of work by members of the APA DSM-IV Advisory Committee
on PTSD, included multiple personality disorder/dissociative identity disorder among the disorders related to “abnormal stress reaction[s].”....

There are several possible explanations for the current study findings. Previous studies have shown that dissociative identity disorder patients essentially universally report high rates of exposure to repeated stressful experiences in early life. The hippocampus is a major target
organ for glucocorticoids, which are released during stressful experiences. It has been hypothesized that prolonged exposure to glucocorticoids could lead to progressive atrophy of the hippocampus. Smaller hippocampal
volume in dissociative identity disorder could thus be related to stress exposure and could represent a neurobiological finding that dissociative identity disorder shares with other stress-related psychiatric disorders such as PTSD....

These findings suggest that early abuse associated with a stress-related psychiatric disorder may be related to smaller amygdalar volume. In addition, these findings are in contrast to findings from studies of depression that have shown no differences or larger amygdalar volume in
depressed patients, compared with healthy subjects....

This finding suggests that dissociative identity disorder is associated with relatively greater volume reductions in the amygdala than in the hippocampus....

full text
http://userwww.service.emory.edu/~jdbremn/papers/DID_MRI.pdf