PSAT346 Persistent Fluctuation Between Hypothyroidism and Hyperthyroidism in a Patient with Both Hashimoto's Thyroiditis and Graves’ Disease: Challenges in Diagnosis and Treatment Approach

Abstract

Abstract Introduction The two most common autoimmune disorders affecting the thyroid gland, namely Graves’ disease and Hashimoto's thyroiditis, represent opposite ends of the same spectrum. They can rarely co-exist in the same patient (1) leading to an unpredictable clinical course and pose a therapeutic challenge, necessitating close monitoring. We present a unique case of a female who switched multiple times between a hypothyroid and hyperthyroid state due to the co-existence of both Hashimoto's thyroiditis and Graves’ disease. Case Description A 78-year-old Caucasian female was diagnosed with hypothyroidism in 2011 by her primary care physician and was started on levothyroxine 50 mcg daily. The TSH level prior to initiation of levothyroxine therapy is unknown, but the first documented TSH level while on therapy in June 2012 was 0.347 uIU/ml (0.45-4.50), free T4 1.1 ng/dl (0.8-1.8) and free T3 3.4 pg/ml (2.3-4.2). Levothyroxine was lowered to 25 mcg daily but repeat TSH was 0.01 uIU/ml in February 2013 and the levothyroxine was discontinued. The TSH level rose to 7.35 uIU/ml in December 2014 and levothyroxine was restarted. However, subsequent dose reduction was required followed by discontinuation due to persistently suppressed TSH levels and the TSI antibody during that time was elevated at 24.10 IU/L (0.00-0.55). Patient established care at our endocrinology clinic in 2019. Initial laboratory findings showed suppressed TSH <0.005 uIU/ml (0.30-4.00), elevated free T3 4.72 pg/ml (2.00-4.40), normal free T4 1.70 ng/dl (0.80-1.80) and elevated TSI antibody 15.50 IU/L. Radioactive iodine uptake scan showed high normal 24 hour uptake at 32% (10-35%) with mild heterogeneous distribution of the radiotracer throughout both lobes of the gland with diminished uptake in the right lower lobe, which corresponded to a 1.3 cm nodule that was biopsied and reported to be Bethesda category II. Patient was initiated on methimazole 5 mg daily. In June 2019, labs showed elevated TSH 6.91 uIU/ml, low free T4 0.74 ng/dl and free T3 2.01 pg/ml. Methimazole was held, and labs repeated after a few weeks, did not change significantly. In September 2020, levothyroxine 25 mcg daily, was initiated due to fatigue symptoms and an elevated TSH 10.61 uIU/ml with low FT4 0.8 ng/dl. Patient did not follow up for a while after that. In December 2021, levothyroxine was increased to 50 mcg daily in response to an elevated TSH 12.91 uIU/ml. The TPO and TSI antibodies remain elevated at 210 IU/ml (0-34) and 9.08 IU/L respectively. Conclusion Our case highlights the diagnostic and therapeutic challenges encountered when both Hashimoto's thyroiditis and Graves’ disease co-exist in the same patient. Reference (1) Alvin Mathew A, Papaly R et al. Elevated Graves’ Disease-Specific Thyroid-Stimulating Immunoglobulin and Thyroid Stimulating Hormone Receptor Antibody in a Patient With Subacute Thyroiditis. Cureus 13(11): e19448. doi: 10.7759/cureus.19448 Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.