Priya Vaidyanathan and Paul Kaplowitz * Children with hyperthyroidism younger than age 7 require higher mg / kg doses of methimazole to normalize free T 4 compared to older children

Background: Hyperthyroidism is much less common in children < 7 years vs. older children and less well studied. It was our impression that the youngest patients needed a higher weight-based dose of methimazole (MMI) to achieve euthyroidism. Objectives: To compare the mean MMI dose needed to normalize free T4 in younger ( < 7 years) vs. older children and the time taken to normalize free T4. Methods: Based on chart review (2004–2012), patients were divided into groups based on age at diagnosis: < 7 years (n = 13), 7–12 years (n = 30) and > 12 years (n = 40). Follow-up visits were reviewed until free T4 normalized. Results: The mean dose of MMI (mg/kg/day) needed to normalize free T4 was 0.71 (±0.29) in the < 7 group, significantly higher vs. the two older groups: 0.50 (±0.22) and 0.44 (±0.24). Months taken to achieve a euthyroid state was significantly longer in children < 7 (6.23±3.91) vs. the older groups (3.10±2.12 and 3.18±2.86 months). Conclusion: Hyperthyroid children diagnosed before age 7 required higher initial doses of MMI and took a longer time to become euthyroid than older patients. Clinicians should consider starting with higher weight-based MMI doses when treating younger patients to more rapidly normalize free T4.