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
Which of the following OCD carries worst prognosis to treatment? 
Select and explain. 
A. Pathological doubt, B. Contamination, C. Hoarding disorder, D. Obsessive thought disorder
C: Hoarding disorder
Answer: C: Hoarding disorder 
Explanation: Hoarding disorder is characterized by acquiring and accumulating useless things attaching them with emotional importance.
Exposure and response prevention which is a standard treatment for OCD, is often found ineffective and hence it carries worst prognosis.