CONTEXT: Congenital hypothyroidism (CH) may arise from dual foci thyroid ectopia. OBJECTIVE: To ascertain the incidence of dual ectopia in CH and compare the phenotype to single ectopia or thyroid agenesis. DESIGN AND SETTING: Single center, retrospective study of babies referred through UK Newborn Bloodspot Screening between 2006 and 2012. PATIENTS: A total of 837 377 babies were screened for CH, with 730 referred for diagnostic confirmation (134 thyroid ectopia, 73 thyroid agenesis). INTERVENTION: Thyroid isotope scans were classified as single or dual ectopia. Biochemical, clinical, and sociodemographic data were collected. MAIN OUTCOME MEASURES: The incidence of thyroid dual ectopia and comparison of clinical parameters with single ectopia and agenesis. RESULTS: Thyroid ectopia occurs with an incidence of 16 per 100 000 births. Twenty-one of 134 (15.7%) babies with thyroid ectopia had dual foci, an incidence of 2.5 per 100 000 births. Dual ectopia infants had lower mean bloodspot TSH compared to single ectopia and agenesis groups (P < .001). On venous sampling, the ectopia group differences were absent, but the difference with the agenesis group remained (TSH, P < .001; free T4, P < .001). There were no between-group differences for gestation, ethnicity, maternal age, or levothyroxine requirements at 12 months. CONCLUSIONS: Thyroid dual ectopia has an incidence of 2.5 per 100 000 births. Early functional activity in the ectopia groups with detectable serum free T4 concentrations is lost at 12 months when T4 requirements are the same as the agenesis group.
CONTEXT: Congenital hypothyroidism (CH) may arise from dual foci thyroid ectopia. OBJECTIVE: To ascertain the incidence of dual ectopia in CH and compare the phenotype to single ectopia or thyroid agenesis. DESIGN AND SETTING: Single center, retrospective study of babies referred through UK Newborn Bloodspot Screening between 2006 and 2012. PATIENTS: A total of 837 377 babies were screened for CH, with 730 referred for diagnostic confirmation (134 thyroid ectopia, 73 thyroid agenesis). INTERVENTION: Thyroid isotope scans were classified as single or dual ectopia. Biochemical, clinical, and sociodemographic data were collected. MAIN OUTCOME MEASURES: The incidence of thyroid dual ectopia and comparison of clinical parameters with single ectopia and agenesis. RESULTS:Thyroid ectopia occurs with an incidence of 16 per 100 000 births. Twenty-one of 134 (15.7%) babies with thyroid ectopia had dual foci, an incidence of 2.5 per 100 000 births. Dual ectopia infants had lower mean bloodspot TSH compared to single ectopia and agenesis groups (P < .001). On venous sampling, the ectopia group differences were absent, but the difference with the agenesis group remained (TSH, P < .001; free T4, P < .001). There were no between-group differences for gestation, ethnicity, maternal age, or levothyroxine requirements at 12 months. CONCLUSIONS:Thyroid dual ectopia has an incidence of 2.5 per 100 000 births. Early functional activity in the ectopia groups with detectable serum free T4 concentrations is lost at 12 months when T4 requirements are the same as the agenesis group.