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: Medicine
The MOST severe complication of idiopathic hyper-eosinophilic syndrome is: 
Select and explain. 
A. Endocardial fibrosis, B. Eosinophilic gastroenteritis, C. Interstitial pneumonia, D. Bone marrow failure
A: Endocardial fibrosis
Answer: A: Endocardial fibrosis 
Explanation: The most severe complicaions are involving hea and CNS. In the hea pathologic changes leads to thrombosis, endocardial fibrosis and restricve cardiomyopathy. Ref: Harrisons Principles of Internal Medicine, 18th Edition, Page 481