Endocrine Abstracts

Introduction: While Graves’ disease is a common cause of thyrotoxicosis, tyroid hormone resistance (THR) is a rare cause of high thyroid hormones. Coexistence of Graves’ disease and THR which can cause quite a lot of difficulties in diagnosis and treatment was reported very rarely in the literature. Here, we report a patient with THR and Graves’ disease in whom remission was achieved with medical therapy.

Case: A 38-year-old woman applied to our clinic with sweating and palpitation. Familial history revealed THR in her sister. Her body temperature was 37.2°C, heart rate was 120 beats/minute, respiratory rate was 18 breaths/minute and blood pressure was 120/70 mmHg. In laboratory examinations, thyroid stimulating hormone (TSH) was 0.018 mU/l (0.55-4.78 mU/l), free T4 was 2.64 ng/dl (0.89-1.7 ng/dl), free T3 was 9.05 ng/l (2.3-4.2 ng/l), anti-thyroglobulin and anti-thyroid peroxidase were negative, TSH receptor antibody (TRAB) was positive. Thyroid ultrasonography revealed chronic thyroiditis and technetium 99m scintigraphy showed heterogeneous activity. When laboratory results were examined retrospectively, we saw that in previous 3 years, her TSH, free T4 and free T3 ranged between 0.84-1.75 mU/l, 1.87-2.12 ng/dl and 4.77-5.86 ng/l, respectively. Thus, the patient had the lowest TSH value and highest free thyroid hormones in her life when she applied. With the current laboratory results and imaging findings, Graves’ disease was diagnosed. Methimazole and propranolol treatment was started. Methimazole was switched to propylthiouracil due to the development of skin rash. Owing to family history and her previous thyroid hormone profile, THRB gene mutation analysis was requested from the patient. Heterozygous c.1001T>C mutation was detected. Under treatment, her symptoms resolved, TSH returned to normal, free T3 and T4 were followed as close to the upper limit or slightly elevated. The patient’s propylthiouracil medication therapy was discontinued after 18 months. At the time of discontinuation her TSH was 0.96 mU/l, free T3 was 6.05 ng/l, free T4 was 1.98 ng/dl, TRAB was negative. At the last visit, 2 years had passed since drug discontinuation and her serum TSH was 0.51 mU/l, free T3 was 4.86 ng/l and free T4 was 1,50 ng/dl.

Discussion: Treatment with anti-thyroid drugs remains the primary choice for Graves’ hyperthyroidism complicated by THR. The optimal treatment is to normalize TSH while keeping free thyroid hormones slightly higher than the upper limit. Iodine therapy and surgery are not generally recommended, since they may induce severe hypothyroidism.