PTSD results from exposure to a range of extreme stressors but one of its most common associations has been with war and combat, as described in historic and literary accounts. The name, etiology, cause, diagnosis, and treatment of the disorder all have been subject to considerable debate and controversy over the years (Wilson et al., 2001). PTSD develops in a significant minority (up to a third) of individuals who are exposed to extreme stressors, and symptoms of PTSD almost always emerge within days of the trauma. More information on the prevalence, etiology, and symptomatology of PTSD is provided in an upcoming IOM report, Gulf War and Health: Physiologic, Psychologic, and Psychosocial Effects of Deployment-Related Stress (Institute of Medicine, 2007a).

The Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association (APA) first formally defined PTSD in 1980 in the DSM-III. The definition was revised in 1987 (DSM-III-R) and 1994 (DSM-IV) (APA, 1987, 1994). There was no change in the 2000 DSM-IV-TR (APA, 2000). The DSM-IV defines PTSD by several criteria: experiencing a traumatic stressor (“experienced or witnessed actual or threatened death, injury, or threat to the physical integrity of self or others”) reacted to with “intense fear, helplessness, or horror” (Criterion A); intrusive recollections of the traumatic event (Criterion B); avoidance and numbing (Criterion C); and hyperarousal in the form of extreme startle reflex, inability to fall or stay asleep, and so on (Criterion D); the symptoms must be experienced for at least 1 month (Criterion E); and the symptoms cause distress or impairment in various areas of functioning (Criterion F) (APA, 2000). According to the DSM-IV, PTSD may be acute (symptom duration under 3 months) or chronic (symptom duration of 3 months or longer), and its onset may be delayed (occurring at least 6 months after exposure). The definition of PTSD does not recognize subtypes classified by type of trauma, such as combat versus civilian or simple exposure versus repeated exposure.

PTSD is heterogeneous with respect to symptom expression, severity, and chronicity. This heterogeneity may have important implications for response to specific treatments. Those in whom the predominant disturbance is insomnia might require a different treatment than persons in whom the predominant disturbance is avoidance. The course of PTSD may vary in duration of symptoms and level of disability, with a considerable proportion of persons with the disorder experiencing disabling symptoms for years (Kessler et al., 1995).

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