[A case of postpartum silent thyroiditis misapprehended as malignant lymphoma of the thyroid].

A case of postpartum silent thyroiditis misapprehended as malignant lymphoma of the thyroid is reported. The patient was a 30-year-old female who had received irradiation therapy to the neck for malignant lymphoma 9 years ago. She was referred to our department owing to a struma accompanying rapid aggravation of chronic thyroiditis after delivery. The mechanism of this case was possible to be explained by immune rebound theory. It was difficult to make differential diagnosis of this case from malignant lymphoma of the thyroid clinically and cytologically when immune rebound phenomena with invasion of lymphocyte and appearance of lymph follicle were the strongest. Immune state of the patients with chronic thyroiditis accompanied by morphological change should be taken into consideration in the process of making diagnosis of malignant lymphoma of the thyroid.