Graves' Disease and Coexisting Struma Ovarii: Struma Expression of Thyrotropin Receptors and the Presence of Thyrotropin Receptor Stimulating Antibodies

Struma ovarii is a rare cause of hyperthyroidism and particularly rare in patients with coexisting Graves' disease. We describe a 28-year-old female who presented with symptoms and signs of hyperthyroidism (free thyroxine [FT₄] 39 pmol/L, thyrotropin [TSH] < 0.05 mU/L) and associated ophthalmopathy, consistent with Graves' disease. The patient relapsed twice: once after initial successful management with carbimazole and subsequently after subtotal thyroidectomy. Radioisotope scanning showed focal uptake bilaterally in the neck and believing this was the source of thyroid hormone excess, carbimazole was restarted. A left ovarian mass was found on ultrasound during the investigation of unrelated nephrotic syndrome resulting from focal segmental glomerulosclerosis. A 555-g struma ovarii was removed surgically. Hypothyroidism developed postoperatively(FT₄ 9.7 pmol/L, TSH 36 mU/L). Circulating TSH receptor stimulating antibodies were positive and immunohistochemical studies confirm the presence of TSH receptors on the struma ovarii. The demonstration of TSH receptors on the struma ovarii increases previous speculation that struma ovarii growth and function may be augmented by the circulating TSH receptor stimulating antibodies of Graves' disease.