Posttraumatic Stress Disorder

Epidemiology

PTSD is an anxiety disorder that affects approximately 7% to 9% of Americans at some points in their lifetimes. Its prevalence rate is even higher among individuals who have been exposed to mass trauma such as U.S. citizens 2 months after the 9/11 terrorist attacks (17%) and survivors of the Oklahoma City bombing (34%). In other parts of the world, the prevalence of PTSD varies widely (range = 1% to 37%), with higher rates found in countries where civilians are exposed to ongoing violence and unrest. Women are twice as likely to develop PTSD than are men. Among treatment-seeking populations, such as in psychiatric and primary care clinics and in certain specialty settings (including gastrointestinal, gynecological, neurological, pain, and eating disorder clinics), PTSD also appears to be more prevalent than in the general population.

Trauma and Risk Factors

PTSD develops following exposure to traumatic events, but not everyone exposed to trauma develops PTSD. An event is considered to be “traumatic” if it poses a threat of death or serious injury or a threat to the physical integrity of self or others. Common examples include war, terrorism, physical or sexual assault, natural disaster, childhood neglect and abuse, sudden and unexpected death of a loved one, and other catastrophic events. It has been estimated that the majority of the population will experience at least one extremely traumatic event during the course of [Page 473]their lives and that approximately 25% of trauma survivors will develop PTSD. For men, combat exposure and witnessing someone being injured or killed are the most common traumatic experiences associated with PTSD; for women, rape, sexual molestation, and childhood physical abuse are among the most frequent causes of PTSD.

Although trauma is probably the strongest risk factor for developing PTSD, with more severe and early-onset traumatic events being more predictive of PTSD, other factors also confer a higher risk than do others. Female gender, family history of psychiatric disorder, past history of behavior or psychological problems, substance abuse disorder, and neurotic or antisocial personality all are associated with increased risk of PTSD.

Neurobiological Mechanisms

Many studies suggest that PTSD may represent a state of sustained fear and arousal following trauma, influenced by neurochemical and neuroanatomical abnormalities as well as by genetic vulnerabilities. Some neurobiological abnormalities are well established, including adrenergic hyperactivity and enhanced negative feedback of the hypothalamic–pituitary–adreno-cortical (HPA) axis, the body's stress response system that controls levels of cortisol and other important stress-related hormones. Dysregulations in other neurochemical pathways, including those for corticotropin-releasing factor (CRF), serotonin, dopamine, γ-aminobutyric acid (GABA), glutamate, and opioids, have also been indicated. Neuroanatomically, volumetric reductions in certain brain structures, such as the hippocampus, have been shown using neuroimaging studies. Furthermore, data from family and twin studies also implicate a genetic contribution to the development of PTSD.

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