SUN-197 T3-Predominant Graves’ Disease With Rapidly Enlarging Asymmetric Goiter in a Pediatric Case: An Unusual Entity

Abstract Disclosure: N. Bangash: None. J.A. Siddiqui: None. B. Shah: None. IntroductionPediatric Graves’ disease (GD) can be severe and associated with fewer remissions and more relapses compared to adults. Initial treatment is usually with oral antithyroid drugs if tolerated, for about 2 years. A small cohort may have T3 predominant Graves’ disease (T3PGD), which is defined as sustained high levels of free T3 with normal or paradoxically low Free T4 during treatment. T3PGD is often more severe and associated with elevated thyroid receptor antibodies (TRAB). The underlying mechanism is poorly understood. Objective To present a rare case of T3PGD, characterized by severe hyperthyroidism, asymmetric goiter, and unusual clinical progression, highlighting the importance of early diagnosis and intervention.MethodsWe report a 12-year-old girl who presented with fatigue, diarrhea, palpitations. Lab tests revealed severe hyperthyroidism with suppressed TSH (<0.005 μIU/mL N 0.5-4.5), high total T3 (651 ng/dL N 40-193), free T4 (7.7 ng/dL,N 0.8-1.5) and elevated TRAB and thyroid-stimulating immunoglobulin (TSI). Ultrasound showed an enlarged thyroid gland with increased vascularity (R: 7.1 x 1.9 x 2.8 cm, vol. 19.6 cc; L 7.2 x 1.7 x 2.2 cm, vol. 14 cc). Hence, methimazole (MMZ) 10 mg twice daily and propranolol were started.After 2 months of treatment, labs showed low TSH (0.2 μIU/mL) with low free T4 (0.3 ng/dL) and total T3 (93 ng/dL). The MMZ was decreased to 5 mg twice daily. However, the symptoms continued to worsen. At 6 months, she had a visibly asymmetric, firm, large thyroid goiter and bilateral proptosis, with congested conjunctiva and lid lag. Her TSH was 0.10 μIU/mL, with elevated free T3 (5.86 pg/mL, N 1.6-3.9) and total T3 (256 ng/dL), and paradoxically low free T4 (0.2 ng/dL). Her TRAB remained elevated, and serum iodine was low <20 (Normal 40-92 ug/L). Ultrasound showed further asymmetric growth (R: 8.4 x 3.9 x 5.1 cm, vol. 86.8 cc; L 8.3 x 2 x 3.7 cm, vol. 31.9 cc). Her MMZ was increased to 7.5 mg twice daily. Elevated T3 with rapidly enlarging asymmetric goiter, continued symptoms, suppressed T4 and TSH, high TRAB on MMZ led to the diagnosis of T3PGD. ResultsDespite MMZ treatment, the right thyroid vol. increased fourfold, and the left thyroid vol. doubled over a 6-month period, necessitating total thyroidectomy. Histopathology confirmed GD. Postoperatively, hypothyroidism developed and received levothyroxine 125 mcg daily, normalizing thyroid function with dose adjustments. ConclusionT3PGD is a rare, severe variant of GD that requires a high clinical suspicion, particularly in cases of asymmetric goiter and elevated TRAB titers. Early diagnosis and aggressive management, including consideration of definitive surgical treatment are critical to optimizing outcomes. This case highlights the aggressive nature of T3PGD and underscores the need for further research into its underlying mechanisms, including the role of iodine and autoimmune processes. Presentation: Sunday, July 13, 2025