Unilateral Graves' Disease in a Bilobar Thyroid Gland: A Very Unusual Cause of Hyperthyroidism

Graves' disease (GD) is an autoimmune condition that affects both thyroid gland lobes. Patients with GD with unilateral thyroid scan uptake are rare. These patients present with classic Graves' symptoms, occasionally with Graves' ophthalmopathy characteristics and increased thyroid hormones, and scintigraphic assessment reveals radiotracer uptake in only 1 lobe of the thyroid gland. In this case, a 48-year-old female presented with symptoms and signs indicative of thyrotoxicosis. Laboratory results revealed that TSH was undetectable, whereas free thyroxine and free triiodothyronine were in the high-normal range. Positive results were observed for both thyroid-stimulating Ig and TSH receptor antibodies. Ultrasonography of the thyroid gland revealed an enlarged left lobe with heterogeneous echotexture and a hyperemic gland without any focal lesions, distinct nodules, or cysts. Thyroid scintigraphy revealed enlarged and increased radioisotope uptake in the left lobe and decreased uptake in the right lobe, with no hot or cold nodules. The most likely diagnosis was unilateral GD. The patient was administered carbimazole and within 8 weeks had improved clinically and biochemically.