Background: Hairy cell leukemia (HCL) presents with pancytopenia, splenomegaly, and monocyte-like hairy cells with eccentric nucleus in blood smear and bone marrow. Cladribine, pentostatin and interferon alpha are used for therapy. Fever is usually associated with infections of bacterial or
viral origin. High mortality and morbidity are associated with bacterial infections in those who are untreated.
Case Report: We report a 38 years old male HCL patient representing with fever and pain on the neck. The diagnosis of febrile neutropenia and subacute thyroiditis were made. For the therapy of subacute thyroiditis, paracetamol and propranolol were given. The patient had refused to take chemotherapy, so, when the thyroid function test reached the normal ranges, splenectomy was performed with the support of erythrocytes and platelet aphaeresis. At the follow up, the patient was in good state of health.
Conclusions: Subacute thyroiditis should be kept in mind especially in HCL representing with fever and pain over the thyroid. According to our search on medical database, this is the first reported case of HCL with subacute thyroiditis in literature.

Keywords: hairy cell leukemia, subacute thyroiditis, Splenectomy