A 23 year old man after a road traffic accident presents to a psychiatrist with anger, disturbed sleep and avoidance. Which of the following feature helps in the differentiation of post traumatic stress disorder (PTSD) from other disorders?

Post traumatic stress disorder is characterized by a constellation of re experiencing a traumatic event, avoidance of stimuli associated with trauma and presence of hyperarousal symptoms. Among these the pathognomic feature of PTSD are episodes of re experiencing in the form of flash backs, night mares or intrusive memories, and patients often try to avoid these memories both cognitively and behaviorally. Although flash backs and nightmares are a symptom of PTSD, on their own they could be seen in various other neurotic or emotional disorders. Hence the answer is Recall of events and avoidance of similar experiences in PTSD. Diagnosis of PTSD requires presence of these 3 features for more than 1 month.