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
How to differentiate between psychological and organic erectile dysfunction ? 
Select and explain. 
A. Nocturnal penile tumescence, B. PIPE therapy, C. Sildenafil induced erection, D. Squeeze technique
A: Nocturnal penile tumescence
Answer: A: Nocturnal penile tumescence 
Explanation: Ans. A. Nocturnal penile tumescenceOne of the impoant method to distinguish psychogenic impotence from organic imPotence is nocturnal penile tumsescence & early morning erection which are preserved in psychogenic impotence but not in organic cause of impotence.