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 50 - year - old male presents with a three year history of irritability, low mood, lack of interest in surrounding and general dissatisfaction with everything. There is no significant disruption in sleep and appetite. He is likely to be suffering from: 
Select and explain. 
A. Major depression, B. No psychiatric disorder, C. Dysthymia, D. Chronic fatigue syndrome
C: Dysthymia
Answer: C: Dysthymia 
Explanation: Long standing and less severe depressive symptoms along with normal sleep and appetite indicates Dysthymia. Dysthymia: Symptoms of depression are present but are not severe enough to cause socio-occupational disturbance with duration of more than 2 years