The relationship between changes in
glucose tolerance with treatment of
hyperthyroidism and various factors that might be relevant to carbohydrate metabolism were investigated in 64
hyperthyroid patients with abnormal
glucose tolerance, including 35 cases with fasting plasma
glucose (FPG) levels of 140 mg/dl or more. All patients had diffuse toxic
goiter. After correction of the
hyperthyroidism,
glucose intolerance improved in almost all cases, even in cases with fasting
hyperglycemia, but
diabetes mellitus in patients with FPG above 140 mg/dl and/or delta IRI/delta PG X 30' during a 50-g oral
glucose tolerance test below 0.10, persisted. Patients who showed diabetic
glucose tolerance even after remission from thyroid dysfunction had significantly lower delta IRI/delta PG X 30' values and a higher incidence of family histories of
diabetes mellitus than those not showing diabetic
glucose tolerance. There were no significant differences in serum T3 and T4 levels between these two groups of patients. The findings suggest that predisposition to diabetes may be an important factor in persistent
glucose intolerance in the
hyperthyroidism of
Graves' disease. The FPG and delta IRI/delta PG X 30' values may be useful in predicting which patients with
hyperthyroidism will have permanent diabetes.