Hypereosinophilic syndrome: progression of peripheral neuropathy despite controlled eosinophil levels.

Idiopathic hypereosinophilic syndrome (HES) is a disorder of the hematopoietic system, characterized by persistent elevation in the total eosinophil count (> 1500/microliter) for over 6 months, associated with organ damage and no detectable underlying cause. Treatment is centered on the reduction of total circulating eosinophils, which generally leads to remission of symptoms. We report a 68-year-old female patient with HES and peripheral neuropathy, presenting with cutaneous lesions, mental changes, cardiac and pulmonary symptoms, followed by right foot drop and eventually paraparesis, which caused an inability to ambulate. Weakness progressed to include the upper extremities despite adequate control of eosinophilia by steroids. Worsening of the peripheral neuropathy can occur despite lowering of the eosinophil levels.