Hypereosinophilia as the presentation of metastatic medullary thyroid carcinoma: a remarkable event.

Hypereosinophilic syndrome is a rare disorder characterized by persistent eosinophilia combined with organ system dysfunction. This report is of a 37-year-old man who had eosinophilia, periodic fever, weight loss, and generalized bone pain. A small nodule in left lobe of thyroid was detected in his physical examination. The patient underwent surgery and histopathological study, which confirmed that the patient had medullary carcinoma of thyroid. The patient died 6 months after the surgery. Eosinophilia is more commonly seen with benign conditions. However, less frequent but malignant etiologies always should be contemplated.