ESPE Abstracts

We present two cases of preterm newborns affected by autoimmune hyperthyroidism: patient A, a four-day-old male, and patient B, a seven-day-old female. Patient A was born at 33+6 gestational weeks (GW) by eutocic delivery; pregnancy was complicated by maternal autoimmune hypothyroidism. The mother was diagnosed with autoimmune thyroiditis eight years earlier, with positivity for anti- thyroperoxidase antibodies (TPOAb), in the absence of TSH receptor antibodies (TRAb). After an initial phase of hyperthyroidism treated with methimazole, the mother started replacement therapy with levothyroxine (L-T4), which is currently ongoing. During pregnancy, thyroid function remained well controlled with L-T4 but high titer TRAb (146.50 U/L, nv 0.0-1.22) were detected. Therefore, on the third day of life, newborn’s thyroid function and autoimmunity were checked, showing TSH 0.005 mU/L, fT3 12.1 pg/mL, fT4 7.77 ng/dL, TPOAb 429 U/ml (nv <34), anti-thyroglobulin antibodies (TgAb) 33 U/ml (nv <115), TRAb 35.9 IU/L (nv <1.75). Therefore, methimazole was started at 0.6 mg/kg/day on the fourth day of life. Patient B was born at 32+6 gestational weeks by c-section. Her mother suffered from autoimmune thyroiditis with positivity of TPOAb and TgAb, already diagnosed before pregnancy, and requiring L-T4 treatment. At seven days of life, the baby presented with tachycardia, therefore thyroid function tests were performed, showing TSH 0.005 mU/L, fT3 26 pg/mL, fT4 >7.77 ng/dL - TRAb levels were not available. Therefore, therapy with methimazole was started at 0.75 mg/kg/day. Blood tests were run also in the mother revealing normal thyroid function with high titer TPOAb and TgAb, as expected, but, amazingly, elevated TRAb levels were detected as well. The presence of high titer maternal TRAb can cause different clinical presentation (hypothyroidism/hyperthyroidism) in the mother and the child, having an inhibitory or a stimulatory action. We therefore hypothesized that a portion of TRAbs present in the mother could have an inhibitory role. In fact, in case A specific antibodies analysis revealed a predominance of inhibitory TRAbs in the mother and of stimulatory TRAbs in the child. For patient B and her mother, this dosing is currently underway. In conclusion, these two cases highlight that TRAb dosage during pregnancy plays a fundamental role in the early diagnosis of neonatal hyperthyroidism also in mothers affected by autoimmune hypothyroidism in therapy with L-T4, since TRAb activity could play a different role in the mother/newborn.