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 (T4) (p = 0.025). During treatment, 63.3% of diagnosable samples showed unambiguous hyperthyroidism or triiodothyronine (T3) toxicosis, 16.7% elevated free T3 with normal free T4 and T3 levels, indicating borderline hyperthyroidism, and 20% showed thyroid-stimulating hormone (TSH) suppression with normal or low levels of free T4 and free T3, indicating delayed recovery of pituitary TSH secretion. Free T3 levels combined with concurrent TSH levels permit differentiation of mild hyperthyroidism from delayed pituitary recovery.