Abstract
A 55-year-old male, with a positive medical history for hypothyroidism, treated with stable doses for years was admitted with subacute thyroiditis and a feeling of pain and pressure in the neck. Laboratory tests showed decrease in TSH levels, elevated erythrocyte sedimentation rate, and very high antithyroid antibodies. Owing to enlarging goiter and exacerbation in the patient's complaints, he was operated with excision of a fibrotic and enlarged thyroid lobe. Elevated IgG4 plasma levels and high IgG4/IgG plasma cell ratio on immunohistochemistry led to the diagnosis of IgG4-mediated thyroiditis. We concluded that IgG4-thyroiditis and IgG4-related disease should be considered in all patients with an aggressive form of Hashimoto's thyroiditis. LEARNING POINTS: IgG4-related disease is a systemic disease that includes several syndromes; IgG4-related thyroiditis is one among them.IgG4-thyroiditis should be considered in all patients with an aggressive form of Hashimoto's thyroiditis.Patients with suspected IgG4-thyroiditis should have blood tested for IgG4/IgG ratio and appropriate immunohistochemical staining if possible.