This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
For the following causes of sexual dysfunction, select the most likely clinical feature.Can be caused by vascular disease. 
Select and explain. 
A. loss of sexual desire, B. failure of erection with absent nocturnal penile tumescence (NPT), C. absence of emission, D. absence of orgasm with normal libido and erectile function
B: failure of erection with absent nocturnal penile tumescence (NPT)
Answer: B: failure of erection with absent nocturnal penile tumescence (NPT) 
Explanation: Vascular disease, by itself or in conjunction with peripheral neuropathy in DM, is a common cause of erectile dysfunction. The lesions can be in large vessels (aortic occlusion, Leriche syndrome), small arteries, or even in the sinusoidal spaces.