8806 A Case of Autoimmune Thyroid Switching

Abstract Disclosure: J. Case: None. R.V. Chemitiganti: None. D. Suravajjala: None. Autoimmune thyroid disease comprises both hyper- and hypothyroid states including Graves' disease and Hashimoto's thyroiditis, respectively. The predominant antibody activity, demonstrable by thyrotropin receptor antibody, predicts the clinical presentation and treatment; thyrotropin receptor antibodies may act as a stimulatory or inhibitory stimulus upon the thyroid gland recognized as thyroid stimulating antibody(TSAb) and thyroid blocking antibody(TBAb). Rarely patients may transition from a hyperthyroid to a hypothyroid state and vice versa if the predominant antibody activity shifts which may occur due to a variety of mechanisms and characteristics related to each individual patient and treatment course. A 29 year old female presented to establish care for autoimmune thyroiditis. She was diagnosed with Graves' disease at age 19 when pregnant and treated with propylthiouracil; she switched to methimazole for the next six years when her thyroid function normalized and therapy discontinued. Two years later she became concerned with weight gain and her thyroid function was reevaluated demonstrating hypothyroidism and she was treated with levothyroxine 25mcg daily until presentation. Further labwork revealed undetectable TSI, and TPO antibody elevated at 177 u/mL. She became clinically and biochemically euthyroid on levothyroxine 50mcg daily. Switching between hyper- and hypothyroid states is a rare occurrence among patients with may attributable factors. Both antithyroid drugs including methimazole as well as replacement therapy with levothyroxine may alter the antibody milieu and so the predominant ratio and activity among TSAb and TBAb thereby leading to a shift in clinical presentation and thyroid state. Pregnancy may lead to hemodilution contributing to lessening of autoimmune activity which may return following delivery leading typically to a shift from TSAb to TBAb. Uncontrolled hyper- and hypothyroidism may affect dendritic activity leading to altered presentation and increased immune reactivity. The unlikely occurrence of switching from a hyperthyroid to a hypothyroid state based upon autoimmunity as in this patient was likely affected these factors. Recognition of this potential transition and associated factors would lead to beneficial monitoring and possibly development of assays more attuned to this phenomenon with better capability in maintaining a euthyroid state and potentially predicting a transition. Presentation: 6/3/2024