9188 Hashitoxicosis To Graves': A Case Of Fluctuating Thyroid Autoimmunity Induced By The Covid Vaccine

Abstract Disclosure: K. Lamar: None. N. Meda: None. J. Straughan: None. D. John: None. S.K. Suryanarayanan: None. Introduction: Thyroid antibodies are essential for identifying autoimmune thyroid disease. In Graves' disease thyroid stimulating immunoglobulin (TSI) is crucial to diagnosing, guiding treatment, and determining prognosis for ophthalmopathy; thyroid peroxidase (TPO) antibody is likewise crucial in the diagnosis of Hashimoto’s Thyroiditis. Conversion between these two diseases is extremely rare. Case: The patient is a 60-year-old female with a medical history of hypertension, asthma, T2NxM0 low grade gastrointestinal stromal tumor (GIST), and hyperaldosteronism who was referred to the endocrine clinic for “thyroid disorders'' with symptoms including weight gain and palpitations. Her labs showed thyroid stimulating hormone (TSH) <0.01mIU/L, free Triiodothyronine (fT3) 6.5ng/mL, free Thyroxine (fT4) 1.6ng/dL, TPO antibodies 46IU/mL, negative TSI antibodies 102%, and a negative Thyroglobulin antibody (Tg Ab) <1IU/mL. A slightly enlarged thyroid was noted on ultrasound. Radioactive iodine uptake (RAI) was normal with 15% uptake at 6 hours and 25% at 24 hours. These findings led to the diagnosis of Hashimoto thyrotoxicosis. She started methimazole 10mg and atenolol 50mg. One year later, she received the Pfizer mRNA COVID-19 vaccine and had her GIST tumor resected. She then began switching between hyper-, hypo-, and euthyroid states with multiple titrations of her Methimazole dose. Repeat testing demonstrated a positive TPO 41 IU/mL, negative Tg Ab <1, positive TSI 294%, and positive RAI with 47% uptake at 6 hours and 61% at 24 hours, consistent with Graves’ disease. It was found that even minor titration by 2.5mg in her Methimazole led to profound changes in her thyroid laboratory values and symptoms. She underwent total thyroidectomy and was started on levothyroxine with significant improvement. Discussion: This patient initially presented with antibodies as well as low uptake on the radio-iodine scan indicating her state of hyperthyroidism was due to Hashitoxicosis, but then later these tests were repeated and were more indicative of Grave’s disease. This was possibly due to immune challenges in the patient, assay inter-variability of thyroid autoantibodies, or an effect of the patient receiving the COVID vaccine. The phenomenon of TSI antibodies converting from negative to positive has not been well documented previously. The goal of this case was to report an interesting conversion of Grave’s disease identifying antibodies and the importance of evaluating underlying immune challenges which could play a role in altering clinical disease. Presentation: 6/1/2024