RF14 | PSAT114 Conversion from one side of the autoimmune thyroid spectrum to the other: a pediatric clinical challenge

Abstract Introduction Graves disease and Hashimoto thyroiditis represent the two ends of the autoimmune thyroid spectrum. Spontaneous conversion from one to the other is a rare phenomenon, especially in children, and the underlying mechanism is unknown. Changes in the predominance of stimulating versus blocking TSH receptor antibodies (TRAb) has been proposed as a potential etiology.Method: We describe a series of cases of autoimmune thyroid disease in children that converted from one end of the biochemical spectrum to the other Result: Eleven patients of whom 55% were girls and 36% had Down syndrome (DS) were identified. Five (46%) presented with hyperthyroidism (hyper) that spontaneously converted to hypothyroidism (hypo). Four patients (36%) had hypo which converted to hyper while the remaining 2 (18%) presented with Hashitoxicosis (HT) with negative TRAb titers which later converted to hyper. In those who went from hyper to hypo, mean duration of antithyroid drug therapy was 1.8 ± 1.4 years and mean age at initial presentation was 11.0 ± 4.8 years (5-16). Before conversion, all 5 patients had positive TRAb titers with mean of 15.0 ± 4.2 and a mean thyroid peroxidase antibody level of 287.5 ± 389. A period of euthyroidism lasting 2.0 ± 0.8 years was present prior to the development of hypo with a mean TSH of 17.0 ± 25 mU/L (5.8-62). Mean duration of hypo in the second group was 5.0 ± 5.2 years and mean age at initial diagnosis was 6.7 ± 2.8 years (3-10). TSH became suppressed in all 4 patients, TRAb was elevated, and mean free T4 off levothyroxine was 3.3 ± 1.2 ng/dL (2.4-4.6). The two patients with initial HT were 12 ± 2.8 years at diagnosis and converted to hyper after 6.5 ± 0.7 months. Initial mean free T4 was 1.3 ± 0.2 ng/dL and after conversion was 4.6 ± 0.4 ng/dL along with strongly positive TRAb titers (mean of 6.9 ± 6.5). TSH became further suppressed after conversion to hyper (<0.01). More of our patients with DS converted from hypo to hyper than the other direction (75% vs 20%, p=0.01). However, two of them proceeded to have a wavering course between hyper and hypo requiring intensive monitoring and frequent changes in management. Conclusion Although oscillating thyroid function in children with autoimmune thyroid disease is uncommon, it is important for parents and providers to be aware of this entity. The natural history of these cases is extremely variable and clinical management is challenging. Our findings suggest that DS may be a risk factor for the phenomenon of vacillating thyroid function in pediatric patients. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Sunday, June 12, 2022 12:42 p.m. - 12:47 p.m.