IgG4-related disease of the thyroid gland.

IgG4-thyroid-related disease (TRD) represents an uncommon spectrum of diseases, with four subcategories established so far, IgG4-related Hashimoto's thyroiditis, fibrosing variant of Hashimoto's thyroiditis, Riedel's thyroiditis and Graves disease with elevated IgG4 levels. We report the case of a 59-year-old woman presenting with painless cervical swelling and hypothyroidism. Thyroid gland was enlarged and distinctively very hard, with reduced mobility. Neck ultrasonography showed multiple nodularity and diffuse thyroid enlargement, which on CT scan conditioned slight deviation of the airway. Fine-needle aspiration of the biggest nodule was suggestive of lymphocytic thyroiditis. She developed compressive symptoms and was submitted to total thyroidectomy. Histology of the thyroid revealed extensive areas of fibrosis, oncocytic cells and lymphoplasmacytic infiltrates. Immunohistochemistry confirmed the predominance of IgG4-secreting plasma cells. IgG4-TRD is characterised by a rapidly progressive and destructive thyroiditis process. Typical presentation can often mimic malignancy; hence, an opportune recognition of IgG4-TRD may avoid unnecessary burdens.