Smaller amygdala volume is associated with post-traumatic stress disorder (PTSD), according to a study published Nov. 5 in Archives of General Psychiatry. Researchers have not yet determined if the physiological difference is caused by a traumatic event, or if people who naturally have smaller amygdalae are more vulnerable to PTSD.
PTSD affects nearly 14 percent of combat veterans serving in Iraq and Afghanistan, according to the Department of Veterans Affairs. PTSD also is estimated to afflict 6.8 percent of adults in the general population who have suffered abuse, crimes and other traumas over their lifetimes.
Previous research has established the link between smaller hippocampal volumes and PTSD; however, studies of amygdala volume have yielded equivocal results.
Rajendra A. Morey, MD, of Duke University in Durham, N.C., and colleagues designed a study to assess the association between amygdala volume and PTSD. The researchers also sought to collect information that might provide insights about PTSD contributory factors and aimed to confirm the association between smaller hippocampal volume and PTSD.
Morey and colleagues recruited 200 military service members and veterans, consisting of 99 subjects with current PTSD and 101 trauma-exposed controls without PTSD. The researchers collected data about subjects’ depressive symptoms, traumatic life events, combat exposure, alcohol use and current medication use.
Participants underwent 3T MRI, and images were automatically post-processed, segmented and labeled. Hippocampal, amygdala and total intracranial volumes were estimated. The volumetry results showed PTSD diagnosis was associated with smaller volume in the left and right amygdala and left hippocampus, which was not accounted for by PTSD chronicity, trauma load, severity of depressive symptoms, alcohol use or medication status.
The researchers credited their success in establishing the link between amygdala volume and PTSD to two factors: the large sample size and use of automated segmentation. They noted the automated approach sets the stage for replication of results, eliminates variability among different raters and removes manual tracing bias.
The researchers sought to determine whether smaller amgydala volume represented a pre-existing vulnerability factor to PTSD or consequence of PTSD. However, the data did not link trauma load or chronicity with lower amygdala volume, nor did it establish smaller amygdala as a PTSD risk factor. The findings suggest that people with measurably smaller amygdala to begin with are susceptible to PTSD, but more studies are needed to make that determination, Morey noted in a press release.
Morey et al called for additional research, and concluded, “Our results may trigger a renewed impetus for investigating structural changes in the amygdala, its genetic determinants, environmental modulators and the possibility that lower amygdala volume represents an intrinsic vulnerability to PTSD.”