We present a case of probably IgG4-related thyroiditis with lymphadenopathy. The patient was a 70-year-old Japanese female who was undergoing hemodialysis and had undergone a right hemi-thyroidectomy in 1989 due to carcinoma. In December 2010, an ultrasonography study revealed a hypoechoic small lesion in thyroid gland. When the patient was admitted to our hospital in November 2013, the lesion and regional lymph nodes had enlarged and we suspected that they were metastatic thyroid cancer. We performed a residual total thyroidectomy and regional lymph node dissection in August 2014. At that time, lymphoplasmacytic infiltration and fibrosis were observed histopathologically in thyroid tissue. Immunohistochemical studies revealed infiltrated lymphocytes and plasma cells were markedly IgG-positive, and the ratio of IgG4-positive to IgG-positive cells was over 40%. We therefore diagnosed the patient with IgG4-related thyroiditis. The cervical lymph nodes were metastases of papillary carcinoma from 25 years earlier. The patient remains well without any recurrences 33 months after the surgery.
