PSAT345 Neonatal Graves (NG) Affecting 3 Newborns of a Mother Treated with Radioactive Iodine (RAI) for Graves’ Disease (GD)

BACKGROUND: Elevated serum thyrotropin receptor antibody (TRAb) levels often return to baseline one year post RAI therapy but can sometimes take a few years to normalize. Remission rates of TRAb autoimmunity in GD is higher in patients taking antithyroid medications and who have undergone a thyroidectomy compared to RAI(1). The incidence of neonatal hyperthyroidism in mothers treated with RAI is estimated to be 3.6% 18-24 months post RAI.(2) CLINICAL CASE: A 31-year-old female G4A1L3 diagnosed with GD at 24 years old treated with RAI at age 25 and remained on L-thyroxine replacement for hypothyroidism. First pregnancy (P1) age 24: terminated at 11wks gestation. P2 (age 28): Spontaneous vaginal delivery (SVD) induced at 38+4wks due to vaginal bleeding, birth weight (BW) 3750g, APGARS 9/9. Baby had NG and was admitted to NICU. On day 3, her heart rate (HR) was greater than140bpmin and she has lost 9.5% weight below her BW. Blood work showed TSH <0.01mIU/L (N: 0.71-31.5), FreeT4 >64.0pmol/L (N: 13.5-41.3), FreeT3 40.4pmol/L (no neonatal reference range), TRAb 206U/L (<10). Methimazole (MMZ) (0.5mg/kg/day) and propranolol (1mg/kg/day) were initiated. Therapy was discontinued at 5 months postpartum. Maternal TRAb was 405U/L (N <10) in first trimester (T1) and dropped to 248U/L in third trimester (T3). P3 (age 31): C-section at 36+2wks, dichorionic diamniotic twin pregnancy, serial US showed good growth and normal dopplers. Both twins developed NG and required NICU admission. Baby A, 3100g, APGARS 7/8/8, had TSH <0.02mIU/L(N: 0.71-3,1.5), FT4 at ∼54h of life of >90pmol/L(N: 12.4-72.4), FT3 23.7pmol/L, TRAb 25.9IU/L(N: <=1.8), HR 162bpmin. Started on MMZ 0.75 mg BID. TSH normalized 3 months postpartum 1.30 mIU/L, FT4 11.4pmol/L. Baby B, 2850g, APGARS 9/9, had jaundice with elevated bilirubin 182umol/L(N: 10-180). HR 130-150bpmin, TSH <0.02mIU/L(N: 0.71-3,1.5), FT4 >90 pmol/L(N: 12.4-72.4), FT3 19.5pmol/l. TRAB 21.9IU/L(N<=1.8). Recovered after 3 months of therapy with MMZ. Maternal TRAb was 60.5 IU/L in second trimester (T2) and 43 IU/L in T3. CONCLUSION: Women with GD who were previously treated with RAI need to be closely monitored for TRAb activity throughout pregnancy. When TRAb Ab levels remain elevated in the T3, close monitoring and assessment of the fetus is critical. Obstetricians and neonatologists need to be involved in the management of these women. REFERENCES: 1. Laurberg P, Wallin G, Tallstedt L, Abraham-Nordling M, Lundell G, Tørring O. TSH-receptor autoimmunity in Graves’ disease after therapy with anti-thyroid drugs, surgery, or radioiodine: a 5-year prospective randomized study. European Journal of Endocrinology. 2008-01-01 2008;158(1): 69-75. 2. Yoshihara A, Iwaku K, Noh JY, Watanabe N, Kunii Y, Ohye H, et al. Incidence of neonatal hyperthyroidism among newborns of graves’ disease patients treated with radioiodine therapy. Thyroid. 2019;29(1): 128-34. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.