Post-traumatic stress disorder (PTSD) and acute stress disorder (ASD) differ from almost every other psychiatric diagnosis in that they may only be diagnosed with reference to an aetiological event – an external traumatic stressor. ASD occurs immediately after the stressor and is comparatively short-lived, while PTSD is a prolonged abnormal response that may take months to develop. The types of stressor leading to ASD and PTSD are identical and were intended to be tightly defined, involving a perceived threat of death, serious injury or loss of physical integrity.
It is useful initially to distinguish ASD and PTSD from adjustment disorders, which are also diagnosed only after an observable life event. An adjustment disorder may be thought of as a gradual and prolonged response to stressful changes in a person's life. The range of stressors precipitating an adjustment disorder is potentially much broader than that precipitating ASD or PTSD, as a threat of death or injury is not needed.
Indeed, a ‘threat’ as such is not needed, as the event may be a loss. Events such as job loss or the breakup of a relationship may lead to an adjustment disorder, as well as threats such as accidents or assaults. The diagnostic criteria for adjustment disorder do not specify what the immediate response, if any, to the precipitating stressor must be.