Abstract
A biological abnormality found to be associated with posttraumatic stress disorder (PTSD) may be, among other things, a pretrauma vulnerability factor, that is, it may have been present prior to the event's occurrence and increased the individual's likelihood of developing PTSD upon traumatic exposure. Alternately, it may be an acquired PTSD sign, that is, it may have developed after the traumatic exposure, along with the PTSD. We have studied pairs of Vietnam combat veterans and their noncombat-exposed, identical twins in an effort to resolve these competing origins. Combat veterans were diagnosed as current PTSD or non-PTSD (i.e., never had). Average heart rate responses (HRRs) to a series of sudden, loud-tone presentations were larger in Vietnam combat veteran twins with PTSD, but these larger responses were not shared by their noncombat-exposed cotwins, whose responses were similar to those of the non-PTSD combat veterans and their noncombat-exposed cotwins. These results suggest that larger HRRs to sudden, loud tones represent an acquired sign of PTSD. In contrast, increased neurological soft signs (NSSs), diminished hippocampal volume, and presence of abnormal cavum septum pellucidum (CSP) were found in Vietnam combat veteran twins with PTSD and their "high-risk," unexposed cotwins compared to Vietnam combat veteran twins without PTSD and their "low-risk," unexposed cotwins. These results support the conclusion that the latter abnormalities represent antecedent, familial vulnerability factors for developing chronic PTSD upon exposure to a traumatic event.
Highlights
Over the past two decades, posttraumatic stress disorder (PTSD) has been characterized by a number of biological abnormalities
Lesions of the central nucleus of the amygdala have been found to significantly reduce heart rate responses (HRRs) to startling white noise in rats, a finding that led investigators to conclude that the amygdala mediates responses to nonsignal acoustic stimuli, and that acceleratory HRRs can reflect the development of fear during acoustic startle testing
Persons who generally react with greater fear to begin with are likely to have a more intense emotional reaction to traumatic events, which would be more likely to lead to the development of PTSD
Summary
Over the past two decades, posttraumatic stress disorder (PTSD) has been characterized by a number of biological abnormalities. It is tempting to conclude that because PTSD is recognized as being caused by a psychologically traumatic environmental event,[1] any abnormalities found in PTSD patients must have been caused by that event. An abnormality may be an antecedent risk factor for exposure to a traumatic event that could cause PTSD. An abnormality may be an antecedent vulnerability factor for developing PTSD upon exposure to a traumatic event. An abnormality may be the consequence of exposure to the traumatic event alone, in which case it would be found in both PTSD and non-PTSD trauma survivors but not in unexposed persons. The abnormality may be the product of a sequel or complication of PTSD
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