This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mood disorders, Subject name: Psychiatry
A 72 yr. old male lost 10kgs since last 3 months. He had profuse guilt for the mistakes he has done in life and doesn't sleep more than 4 hrs. per day. The probable diagnosis is 
Select and explain. 
A. Schizophrenia, B. Dysthymia, C. Involutional melancholia, D. Anhedonia
B: Dysthymia
Answer: B: Dysthymia 
Explanation: Dysthymia is chronic mild depression in which person have symptoms for more than 2 yrs. Ref: Essentials of postgraduate psychiatry By JN Vyas 1st ed Pg 604-607