Factors predicting the course of diabetes mellitus in hyperthyroid patients

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.