Posttraumatic stress disorder: a model of the longitudinal course and the role of risk factors.

Posttraumatic stress disorder (PTSD) differs from other anxiety disorders in that experience of a traumatic event is necessary for the onset of the disorder. The condition runs a longitudinal course, involving a series of transitional states, with progressive modification occurring with time. Notably, only a small percentage of people that experience trauma will develop PTSD. Risk factors, such as prior trauma, prior psychiatric history, family psychiatric history, peritraumatic dissociation, acute stress symptoms, the nature of the biological response, and autonomic hyperarousal, need to be considered when setting up models to predict the course of the condition. These risk factors influence vulnerability to the onset of PTSD and its spontaneous remission. In the majority of cases, PTSD is accompanied by another condition, such as major depression, an anxiety disorder, or substance abuse. This comorbidity can also complicate the course of the disorder and raises questions about the role of PTSD in other psychiatric conditions. This article reviews what is known about the emergence of PTSD following exposure to a traumatic event using data from clinical studies.