Idiopathic hypereosinophilic syndrome revealed by encephalopathy

Idiopathic hypereosinophilic syndrome (HES) is characterized by persistent hypereosinophilia ( ≥ 1500/mm(3)) with evidence of end-organ damage without a definite underlying cause. Hypereosinophilia-induced encephalopathy is a rare clinical syndrome. We present a male patient with idiopathic HES with distinctive encephalopathy who had hypereosinophilia for more than 6 months. Eosinophils in repeated blood tests were more than 1500/mm(3). He had hematological, brain, bone-marrow, and possible cardiac involvement. Although numerous efforts were made to identify the underlying cause of hypereosinophilia, specific causes could not be found in this patient. Bone-marrow analysis confirmed the diagnosis. The unique features were the prominent involvement of the cerebral cortex and the dramatic response to steroids with marked improvement of eosinophilia and brain function. The mechanisms of hypereosinophilia-induced encephalopathy are discussed.