RELAPSE OF MEDICALLY TREATED INSULINOMA FOLLOWING THE DEVELOPMENT OF THYROTOXICOSIS - AN ASSESSMENT OF POTENTIAL MECHANISMS

Increased thyroid hormone concentrations have been reported to have di sparate effects on insulin sensitivity in man. We describe a 72-year-o ld lady who initially presented with episodic hypoglycemia secondary t o an insulinoma that was controlled by diazoxide. She re-presented 12 months later with a recurrence of the hypoglycemia following the devel opment of thyrotoxicosis. The diazoxide treatment was maintained and p ropranolol was introduced, which prevented further episodes of hypogly cemia. This appeared to be due to a direct effect of propranolol on en dogenous insulin secretion, while whole body insulin sensitivity remai ned unchanged as assessed using the hyperinsulinemic-euglycemic clamp technique. She was later rendered biochemically euthyroid with a combi nation of blocking carbimazole therapy and thyroxine replacement, and this was associated with a marked decrease in insulin sensitivity. Thu s, the principal effect of thyroid hormone excess in this patient was an increase in insulin sensitivity that led to the clinical relapse of the insulinoma.