Diagnostic and statistical manual
PTSD was classified as an anxiety disorder in the DSM-IV, but has since been reclassified as a "trauma- and stressor-related disorder" in the DSM-5. The DSM-5 diagnostic criteria for PTSD include four symptom clusters: re-experiencing, avoidance, negative alterations in cognition/mood, and alterations in arousal and reactivity. International classification of diseases
The International Classification of Diseases and Related Health Problems 10 (ICD-10) classifies PTSD under "Reaction to severe stress, and adjustment disorders." The ICD-10 criteria for PTSD include re-experiencing, avoidance, and either increased reactivity or inability to recall certain details related to the event.The ICD-11 diagnostic description for PTSD contains three components or symptom groups (1) re-experiencing, (2) avoidance, and (3) heightened sense of threat. ICD-11 no longer includes verbal thoughts about the traumatic event as a symptom. There is a predicted lower rate of diagnosed PTSD using ICD-11 compared to ICD10 or DSM-5. ICD-11 also proposes identifying a distinct group with complex post-traumatic stress disorder (CPTSD), who have more often experienced several or sustained traumas and have greater functional impairment than those with PTSD. Differential diagnosis
A diagnosis of PTSD requires that the person has been exposed to an extreme stressor. Any stressor can result in a diagnosis of adjustment disorder and it is an appropriate diagnosis for a stressor and a symptom pattern that does not meet the criteria for PTSD. The symptom pattern for acute stress disorder must occur and be resolved within four weeks of the trauma.
PTSD can also occur after childbirth and the risk increases if a woman has experienced trauma prior to the pregnancy. Prevalence of PTSD following normal childbirth (that is, excluding stillbirth or major complications) is estimated to be between 2.8 and 5.6% at six weeks postpartum, with rates dropping to 1.5% at six months postpartum. Symptoms of PTSD are common following childbirth, with prevalence of 24–30.1% at six weeks, dropping to 13.6% at six months. Emergency childbirth is also associated with PTSD. Genetics
There is evidence that susceptibility to PTSD is hereditary. Approximately 30% of the variance in PTSD is caused from genetics alone. For twin pairs exposed to combat in Vietnam, having a monozygotic (identical) twin with PTSD was associated with an increased risk of the co-twins having PTSD compared to twins that were dizygotic (non-identical twins). Women with a smaller hippocampus might be more likely to develop PTSD following a traumatic event based on preliminary findings. Research has also found that PTSD shares many genetic influences common to other psychiatric disorders. Panic and generalized anxiety disorders and PTSD share 60% of the same genetic variance. Alcohol, nicotine, and drug dependence share greater than 40% genetic similarities.Several biological indicators have been identified that are related to later PTSD development. Heightened startle responses and, with only preliminary results, a smaller hippocampal volume have been identified as possible biomarkers for heightened risk of developing PTSD. Additionally, one study found that soldiers whose leukocytes had greater numbers of glucocorticoid receptors were more prone to developing PTSD after experiencing trauma.