PSAT349 New Onset of Grave's Disease In Background of Hashimoto's Thyroiditis, Autoantibodies Switch Phenomenon; A Case Report.
Authors: Arshad Iqra , Jerez Julia Vargas , Tasneem Zahra 
Published: November 2022

Abstract

Introduction
Hashimoto's thyroiditis and Grave's disease represent the two spectrums of same autoimmune thyroiditis. The evolution from Graves disease into Hashimoto's thyroiditis is the most common scenario. While the conversion from Hashimoto's thyroiditis into Grave's disease is a rare occurrence. Exact incidence of this conversion is unknown because of its rarity. We present the case of a young female who developed full blown grave's disease in background of hypothyroidism secondary to Hashimoto's disease.

Case presentation
56 year old hispanic female with past medical history of osteoarthritis and Hashimoto's thyroiditis (TPO +ve) and euthyroid on levothyroxine 75mcg daily for past 6 years who presented to the Emergency Department with concerns of palpitations and dyspnea on exertion for 4 months. Patient denied any recent change of manufacture and dosage of levothyroxine and reported compliance to medication. Review of symptoms was positive for palpitations, dyspnea on exertion, sleep disturbances, reduced exercise tolerance and unintentional weight loss of 20 lbs over 4 months. Physical exam was notable for tachycardia to 130's at rest, hyper-dynamic precordium with non-displaced heaving apex beat, normal S1/S2, no murmurs/gallops/rubs, visible pulsations in neck bilaterally, pounding pulses throughout the extremities and tremors on out stretched hands; and was negative for exophthalmos, thyromegaly and pedal swelling. EKG showed only Sinus tachycardia; Initial lab work up showed TSH of &lt;0.01mIU/l (0.5-1.5), free T3 of 14.50 pg/ml (1.8-4.6), free T4 of 5.5 ng/dl (0.9-1.8). Patient was educated; levothyroxine was held and she was started on atenolol 25mg daily for symptoms control. Further workup revealed Thyroid stimulating immunoglobulin (TSI) of 5.69 IU/L (0.0-0.55); thyroid receptor antibodies levels of 8.14 IU/L (0.0-1.75); TPO antibodies levels of 20.1 IU/L (&lt;=34.9). Small right upper lobe nodule was found on prior thyroid USG with interval decrease in size on repeat imaging. Radioactive iodine uptake scan was delayed because patient underwent CT pulmonary angiogram at presentation to ED and pulmonary embolism was ruled out. Later scan showed thyromegaly with heterogenous uptake of 82% in both lobes in 24 hours. Patient was diagnosed with Grave's disease. Patient opted for radioactive iodine ablation therapy. Post ablation, her symptoms resolved completely; she developed hypothyroidism and was started on maintenance levothyroxine.

Conclusion
Conversion of Hashimoto's thyroiditis to Graves's disease is a rare phenomenon and in literature review, It has been postulated to be due to a combination of atypical destructive autoimmune thyroiditis and change of thyroid receptor antibodies from blocking (TRAb) to stimulating ones (TSAb), a phenomenon known as "switch" resulting in hyperthyroidism. It is important to note that treatment with thyroxine itself can induce this switch. Clinicians should suspect this possibility in a patient who suddenly becomes hyperthyroid in setting of hypothyroidism so that appropriate management could be offered.
Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.