This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
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? 
Select and explain. 
A. Nightmares about the events, B. Recall of events and avoidance of similar experiences in PTSD, C. Autonomic arousal and anxiety, D. Depression
B: Recall of events and avoidance of similar experiences in PTSD
Answer: B: Recall of events and avoidance of similar experiences in PTSD 
Explanation: 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.