Peripheral blood eosinophilia is a well-known paraneoplastic manifestation, but its underlying mechanism is still unclear. Bone marrow metastasis may be a cause of malignancy-associated eosinophilia. However, there is limited evidence of the relationship between bone marrow metastasis and eosinophilia. Herein, we present a unique case of peripheral blood eosinophilia associated with bone marrow invasion in a patient having a history of papillary thyroid carcinoma. A 68-year old woman showed peripheral blood eosinophilia (91,525/mm3). Since the time she was initially diagnosed as having papillary thyroid carcinoma, eosinophilia had never been found and the other causes of eosinophilia were excluded. A bone marrow study revealed cancer cell infiltration; multiple lymphadenopathies and liver metastasis were also detected. We treated her with steroid; however, her eosinophilia did not respond to steroid and the patient died due to disease progression. Although peripheral blood eosinophilia and bone marrow metastasis are rare findings in patients with papillary thyroid carcinoma, we suggest that eosinophilia might be a sign of the bone marrow metastasis of papillary thyroid carcinoma.

Keywords: Thyroid, Bone marrow metastasis, Eosinophilia