MON-410 Transitioning From Hashimoto’s Thyroiditis to Graves’ Disease

Abstract Disclosure: K. Dy: None. M. Pennant: None. Background: Grave’s Disease and Hashimoto’s thyroiditis are common autoimmune diseases of the thyroid gland. Symptoms of these diseases are on the different end of the spectrum. Conversion between these two have been reported but cases of Hashimoto’s thyroiditis switching to Graves’ disease are rare. In this case, we present a patient with Hashimoto’s thyroiditis who developed hyperthyroidism secondary to Graves’ disease. Clinical Case: A 65-year-old female with medical history of HIV infection on Antiretroviral Therapy and recent Covid-19 Infection in August 2021 was noted to have a low TSH after complaining of hot flashes. No medication was started at that time. Three months after, she complained of cold intolerance, constipation and extreme fatigue. Thyroid function tests showed hypothyroidism with thyroid stimulating hormone at 130.76 mIU/L, free T4 at 0.4 ng/dl and total T3 at 46 ng/dl. The thyroid peroxidase antibody was positive at 269 IU/ml. She was then diagnosed with Hashimoto’s thyroiditis. Levothyroxine 75 mcg/day was started with dose adjustment depending on labs and symptoms. Succeeding labs continued with a pattern of hyperthyroidism, thus her medication was decreased. One year after being diagnosed and eventually discontinuing levothyroxine, she developed sweating, 20-pound weight loss, anxiety, palpitations and neck fullness. Thyroid ultrasound was done revealing nodules on bilateral lobes. Thyroid Stimulating Immunoglobulin was elevated at 13.20 IU/L. Thyroid uptake scan was done two months after and results were consistent with Graves’ disease. Methimazole was initiated and improved her symptoms. About one month since the diagnosis of Graves’ disease, she developed thyroid eye disease. Eye symptoms worsened and sixteen months afterwards, was eventually diagnosed with Myasthenia Gravis. At present, she has not achieved remission and continues to take methimazole. Conclusion: Transition from Hashimoto’s thyroiditis to Graves’ Disease is not well-understood. One theory is that both thyroid stimulating and blocking antibodies are present, and symptoms depend on the prevalent antibody. Multiple factors are thought to affect the affinity, concentration and or development of these antibodies including stress, smoking and viral infections. The presence of HIV or prior infection with Covid-19 infection may increase the likelihood of conversion. Patients who experience this may be at risk of developing other non-thyroidal autoimmune diseases. Transition should be considered in those who are at risk and continue to be hyperthyroid despite discontinuing thyroid hormone medication. Clinicians should not only be aware of this but should also be on alert in monitoring for the development of other autoimmune conditions. Presentation: Monday, July 14, 2025