The clinical presentation of PTSD varies. It is not entirely clear what is seen as a traumatic event and what is not. A life-threatening illness or medical condition is not seen as trauma but medical incidents can qualify as traumatic events (e.g. waking up during surgery), same as a medical catastrophe in one’s child.

Intrusive recollection is not the same as depressive rumination. Intrusive recollection applies to involuntary and intrusive distressing memories. It can be short (e.g. flashback) but can lead to prolonged stress and heightened arousal.

In PTSD, there often is a heightened sensitivity to threats. Developmental regression (e.g. loss of language) may occur in children. PTSD can lead to difficulties in regulating emotions or maintaining stable interpersonal relationships.

The lifetime prevalence of PTSD is 8.7% in the United States and the twelve-month prevalence is 3.5%. These estimates are lower in many other countries (e.g. European countries). Different groups have different levels of exposure to traumatic events. The conditional probability of developing PTSD following a similar level of exposure may differ between groups.

Cultural syndromes (e.g. ataques de nervosia) may influence the expression of PTSD. The risk of onset of PTSD and severity may differ across cultural groups as a result of:

• Variation in the type of traumatic exposure (e.g. genocide).
• The meaning attributed to the traumatic event.
• The ongoing sociocultural context.
• Other cultural factors.

PTSD appears to be more severe if the traumatic event is interpersonal and intentional (e.g. torture). The highest PTSD rates are found among rape survivors (1), military combat and captivity survivors (2) and ethnically and politically-motivated internment and genocide survivors (3). Young children and older adults are less likely to show full-threshold PTSD.

The symptoms and relative predominance of symptoms may vary over time. Symptom recurrence and intensification may occur in response to reminders of the original trauma (1), ongoing life stressors (2) and newly experienced traumatic events (3). PTSD symptoms may exacerbate as result of declining health (1), worsening cognitive functioning (2) and social isolation (3).

Individuals who continue to experience PTSD into older adulthood may express fewer symptoms of hyperarousal (1), avoidance (2) and negative cognitions and moods (3) compared with younger adults. However, adults exposed to traumatic events during later life may display more avoidance (1), hyperarousal (2), sleep problems (3) and crying spells (4) than younger adults exposed to the same traumatic event.

There are several pre-trauma risk factors for the development of PTSD:

1. Temperamental
   This includes childhood emotional problems by age 6 and prior mental disorders.
2. Environmental
   This includes lower socioeconomic status (1), lower education (2), exposure to prior trauma (3), childhood adversity (4), cultural characteristics (5), lower intelligence (6), minority status (7) and family psychiatric history (8).
3. Genetic and physiological
   This includes being female and being younger at the time of trauma exposure.

There are several peritraumatic risk factors for the development of PTSD:

1. Environmental
   This includes the severity of the trauma (1), perceived life threat (2), personal injury (3), interpersonal violence (3) and dissociation during the trauma (5). For military personnel, being a perpetrator is a risk factor.

There are several post-traumatic risk factors for the development of PTSD:

1. Temperamental
   This includes negative appraisal (1), inappropriate coping strategies (2) and the development of acute stress disorder (3).
2. Environmental
   This includes subsequent exposure to repeated upsetting reminders (1), subsequent adverse life events(2) and financial or other trauma-related losses (3).

There is a high comorbidity with other disorders for people with PTSD. Substance use and conduct disorder are common among males. The patterns of comorbidity are different in children and adults. PTSD is different from a lot of other disorders;

1. Adjustment disorders
   This disorder is also about stressors that are not similar to PTSD stressors.
2. Other post-traumatic disorders and conditions
   Other diagnoses and conditions are possible but are excluded if the symptoms are better explained by PTSD.
3. Acute stress disorder
   This disorder is different from PTSD as the duration is 3 days rather than 1 month.
4. Anxiety disorders and obsessive-compulsive disorder
   These disorders are not related to a specific traumatic event and the recurrent thoughts are not related to a trauma.
5. Major depressive disorder
   This should be diagnosed if other PTSD symptoms are absent.
6. Personality disorder
   This should be diagnosed if the interpersonal problems exist independent of a traumatic event.
7. Dissociative disorders
   These disorders are not necessarily preceded by exposure to a traumatic event. If they are, a subtype of PTSD can be considered.
8. Conversion disorder
   This disorder should be diagnosed if the symptoms occur before a traumatic experience.
9. Psychotic disorder
   The flashbacks and hallucinations in this disorder do not have a specific focus on trauma.
10. Traumatic brain injury (TBI)
    This diagnosis should be given if the focus of symptoms is neurocognitive rather than behavioural.