Concomitant Graves' disease and Hashimoto's thyroiditis, presenting as primary hypothyroidism

Hypothyroidism in patients with Graves' disease is usually the result of ablative treatment. We describe a 58 year old man with Graves' ophthalmopathy and pre-tibial myxoedema, who presented with spontaneous primary hypothyroidism. Circulating TSH receptor antibody activity was increased, while thyroid microsomal antibody was detectable in titres greater than one in one hundred thousand. It is likely that the TSH receptor antibody of Graves' disease was ineffective in stimulating hyperthyroidism because of concomitant thyroid destruction due to Hashimoto's disease. Alternatively, primary hypothyroidism could have resulted from the effects of a circulating TSH receptor blocking antibody.