The discrepant findings in the literature concerning prevalence can be largely, but not completely, explained as being due to definitional issues. Little is known about what distinguishes the delayed-onset and immediate-onset forms of the disorder. Continuing scientific study of delayed-onset PTSD would benefit if future editions of DSM were to adopt a definition that explicitly accepts the likelihood of at least some prior symptoms.

Differences in symptoms, trauma exposure, dissociative and emotional reactions to trauma, and subsequent life stress in war veterans reporting immediate-onset or delayed-onset posttraumatic stress disorder (PTSD) or no PTSD were investigated. The role of life stress in delayed-onset PTSD was also studied. Retrospective interviews were conducted with 142 United Kingdom veterans receiving a war pension for PTSD or physical disability. Immediate-onset and delayed-onset PTSD were similar in the number and type of symptoms reported at onset, but the delayed-onset group differed in showing a gradual accumulation of symptoms that began earlier and continued throughout their military career. They were more likely to report major depressive disorder and alcohol abuse prior to PTSD onset. Both groups described similar amounts of trauma exposure, but those in the delayed-onset group reported significantly less peritraumatic dissociation, anger, and shame. Veterans with delayed onsets were more likely than veterans with no PTSD to report the presence of a severe life stressor in the year before onset. In conclusion, the results suggest that delayed onsets involve a more general stress sensitivity and a progressive failure to adapt to continued stress exposure.

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