Sustained fever resolved promptly after total thyroidectomy due to huge Hashimoto's fibrous thyroiditis.

We encountered a 55-year-old female patient with Hashimoto's thyroiditis who showed persistent fever, and could not find any source of fever other than the large nontender goiter. Her fever continued with positive CRP for 6 months. Although we did not assume that the inflammation was related to Hashimoto's thyroiditis, total thyroidectomy was performed for cosmetic reasons; however, fever was resolved immediately after thyroidectomy. Pathological diagnosis was Hashimoto's chronic thyroiditis. Immunohistochemical staining showed that the follicular cells were positive for IL-1alpha, IL-1beta, and TNF-alpha. We believed that fever was induced by inflammatory cytokines produced in thyroid. The case indicated that Hashimoto's thyroiditis with nontender goiter could cause idiopathic fever.