The clinical features of diabetes with coexisting autoimmune thyroid disease.

A study was made of the clinical features of diabetics with coexisting Graves' disease (n = 117) or primary hypothyroidism (n = 98). Those with Graves' disease developed thyroid dysfunction and diabetes at an earlier age than patients with primary hypothyroidism. There was, however, no difference between the two groups in respect of sex ratio nor proportion of subjects requiring insulin treatment. In contrast to the general diabetic population, 87% of diabetics with thyroid disease were female, 56% required insulin treatment and of patients requiring insulin from diagnosis, the median age at diagnosis of diabetes was 36 years. A strong correlation was observed between age at diagnosis of diabetes and that of hyperthyroidism (r = 0.71, p less than 0.001) or hypothyroidism (r = 0.65, p less than 0.001). With increasing age at diagnosis of diabetes the interval between diagnosis of diabetes and thyroid disease diminished. The mean +/- SEM interval between diagnosis of diabetes and that of thyroid dysfunction was longer in hypothyroid (6.7 +/- 1.2 years) than in hyperthyroid diabetics (-2.4 +/- 1.2 years). Neither insulin-dependent nor non-insulin dependent diabetics with associated thyroid disease exhibited a significant seasonal variation in diagnosis or symptomatic onset of diabetes. It is conceivable that where diabetes accompanies autoimmune thyroid disease in the same patient, both conditions may share a common and coincident pathogenesis which is unrelated to acute environmental influences.