Progressive lung involvement during steroid therapy in idiopathic hypereosinophilic syndrome

Hypereosinophilic syndrome (HES) is characterized by a sustained eosinophilia of 1,500/mm³ or more in the absence of any known causes or the signs and symptoms of organ involvement. We report a 64-year-old man with HES initially presenting with involvement of the liver and bone marrow. Despite controlling the eosinophilia by corticosteroid, he developed a cerebral infarction and later progressive interstitial pneumonia. Brain angiography revealed a severe stenosis of the proximal right internal carotid artery (ICA) and a complete obstruction of the intracranial ICA. An open lung biopsy revealed fibrosis and lymphoplasma cell infiltration without eosinophils, which were consistent with nonspecific interstitial pneumonia.