A 48-year-old woman presents with complaints of moderate weight loss over the past 6 months, heat intolerance, palpitations, and fine tremors in the hands. Physical examination reveals the presence of a diffuse goiter and exophthalmos. Which of the following laboratory findings would be expected in this individual?
Correct Answer: Increased plasma concentration of thyroglobulin
Description: The description given above is of an individual with Graves' disease. Hypersecretion of thyroid hormone because of stimulation of the TSH receptor by thyroid-stimulating immunoglobulins results in excessive movement of thyroglobulin from the colloid to the plasma. The presence of exophthalmos is thought to be pa of the autoimmune disorder in Graves' disease. It is postulated that the thyroid and orbital muscles may share a common antigen. Lymphocytic infiltration and inflammation of orbital muscle then produces the ophthalmopathy. Serum T4 is increased in Graves' disease. Because of excessive stimulation of the thyroid by the thyroid stimulating immunoglobulins, radioactive iodine uptake, which assesses iodine trapping, is increased. The increase in free T4 due to hypersecretion by the thyroid shifts the equilibrium between free and bound T4 toward an increase in thyroxine binding globulin (TBG)-bound hormone. Concomitantly, the concentration of unbound TBG falls. Hence, the radioactive T3 in the resin T3 uptake test would preferentially bind to the resin and resin uptake would be increased. Ref: Jaume J.C. (2011). Chapter 2. Endocrine Autoimmunity. In D.G. Gardner, D. Shoback (Eds), Greenspan's Basic & Clinical Endocrinology, 9e.
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