<prompt> The MOST severe complication of idiopathic hyper-eosinophilic syndrome is:Endocardial fibrosisEosinophilic gastroenteritisInterstitial pneumoniaBone marrow failure  <response>: 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 