The MOST severe complication of idiopathic hyper-eosinophilic syndrome is:
Endocardial fibrosis
Eosinophilic gastroenteritis
Interstitial pneumonia
Bone marrow failure
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