A 24-year-old woman presents to the clinic with a two-week history of fatigue, weight loss, diarrhea, and palpitations. She denies any history of recent infections. Her past medical history includes systemic lupus erythematosus. She does not currently take any medications. She does not drink alcohol or take illicit drugs. She occasionally smokes cigarettes. There is a family history of "thyroid issues" on her mother's side. Her vital signs are temperature 37.1°C (98.6°F), blood pressure 118/72 mmHg, pulse 112 beats/min, and respirations 18/min. On physical examination, she has a fine tremor of the hands and warm, moist skin. On palpation, her thyroid gland is diffusely enlarged but not tender to touch. Laboratory tests show elevated free T4 and suppressed thyroid stimulating hormone (TSH) levels. A radioactive iodine uptake scan shows diffuse increased uptake.
A) Autoantibodies to the TSH receptor
The patient presents with symptoms of hyperthyroidism, confirmed by elevated free T4 and suppressed TSH levels. Her history of lupus raises the suspicion of another autoimmune disease. Additionally, the lack of tenderness on palpationof the thyroid gland, her young age, and gender further support this suspicion. The diffuse increased uptake on the radioactive iodine uptake scan is characteristic of Graves' disease, an autoimmune disorder where autoantibodies (thyroid-stimulating immunoglobulins) target the TSH receptor. This leads to negative feedback suppressing TSH due to the overproduction of T4.
Answer choice B: Destruction of thyroid follicles, is incorrect. This would likely result in congenital hypothyroidism or hyperthyroidism depending on the nature of the mutation, but it is less common and not typically associated with the presentation of diffuse increased radioactive iodine uptake and the specific clinical features described.
Answer choice C: Excessive iodine intake, is incorrect. Excessive iodine intake is associated with a higher prevalence of Hashimoto's thyroiditis or subacute thyroiditis. However, excessive iodine intake is a potential precipitating factor but not the mechanism underlying Hashimoto’s thyroiditis. Hashimoto’s thyroiditis leads to hypothyroidism, except when a transient hyperthyroidism is present. High iodine-containing medications such as amiodarone also can precipitate autoimmune thyroiditis.
Answer choice D: Mutation in the TSH receptor gene, is incorrect. This can cause hyperthyroidism, particularly in patients with preexisting thyroid disease (Jod-Basedow phenomenon), but the presentation is less specific for this mechanism. The mechanism develops due to up regulation of Na+/I- cotransporters, resulting in excess reuptake of iodine in the blood stream. TSH levels are high to stimulate the thyroid gland to make hormone.
Answer choice E: Pituitary adenoma secreting TSH, is incorrect. This would result in elevated or inappropriately normal TSH levels despite high free T4 levels. The patient's suppressed TSH makes this diagnosis unlikely.
Key Learning Point
Graves’ disease is the most common cause of hyperthyroidism, in which B cells produce immunoglobulin G (IgG) autoantibodies that stimulate the thyroid’s TSH receptors (making this a type II hypersensitivity reaction).
