Effective methimazole dose for childhood Graves' disease and use of free triiodothyronine combined with concurrent thyroid-stimulating hormone level to identify mild hyperthyroidism and delayed pituitary recovery

Appropriate methimazole dosing for initial treatment of childhood Graves' disease is uncertain. A retrospective chart review was performed on 5 to 17 year-old children treated for Graves' disease. Patients were divided into two groups depending on initial methimazole dosing: low-dose and high-dose regimens using < 0.5 mg/kg/day and > 0.5 mg/kg/day, respectively. The low-dose regimen was effective in 5/12 (42%) of patients and the high-dose regimen was effective in 27/33 (82%) of patients (p = 0.016). There was also a statistically significant dose/time interaction for levels of free thyroxine (T-4) (p = 0.025). During treatment, 63.3% of diagnosable samples showed unambiguous hyperthyroidism or triiodothyronine (T-3) toxicosis, 16.7% elevated free T-3 with normal free T-4 and T-3 levels, indicating borderline hyperthyroidism, and 20% showed thyroid-stimulating hormone (TSH) suppression with normal or low levels of free T-4 and free T-3, indicating delayed recovery of pituitary TSH secretion. Free T-3 levels combined with concurrent TSH levels permit differentiation of mild hyperthyroidism from delayed pituitary recovery.