A hard thyroid mass due to plasma cell granuloma

Plasma cell granuloma involving the thyroid is very rare. A 29-year-old man with type 1 diabetes mellitus presented with a one-week history of fever, sore throat, neck tenderness and dysphagia. Antibiotics were given but over the next two weeks a hard 8 cm mass in the left lobe of the thyroid developed. Fine needle aspiration was not diagnostic and surgical exploration revealed an inflammatory process arising from the left lobe of the thyroid involving the left sternothyroid muscle and parapharyngeal spaces. Histology of multiple biopsies showed plasma cell granuloma. Immunoperoxidase staining demonstrated the presence of IgG, IgM and IgA with predominance of IgG. The residual mass resolved and was impalpable after four weeks. Plasma cell granuloma should be suspected when there is a rapidly developing hard thyroid mass. Open biopsy/removal and histological confirmation are mandatory and residual disease may resolve within weeks.