The definition of true recurrence of pituitary-dependent Cushing's syndrome after transsphenoidal operation

Two patients are described with pituitary-dependent Cushing's syndrome who had successful transsphenoidal selective removal of basophil microadenomas. After a period of adrenal insufficiency the clinical signs and the cortisol secretion rate became normal after 12-18 months, together with the return of a normal feedback response to glucocorticoids (dexamethasone suppression), a normal diurnal rhythm of plasma cortisol, and a normal response to stress (increase of plasma cortisol to insulin-induced hypoglycaemia). However, pituitary-dependent Cushing's syndrome recurred 38 and 56 months after operation. This was preceded by gradual changes of the results of the dexamethasone tests, disappearance of the diurnal rhythm of cortisol, and of the responses of plasma cortisol to hypoglycaemia. 'True recurrence' should be defined as the return of the clinical and biochemical characteristics of Cushing's syndrome after a successful transsphenoidal operation, with a normal hypothalamic-pituitary-adrenal axis as evidenced by a normal response to dexamethasone, a normal diurnal rhythm of cortisol and a normal increase of plasma cortisol with insulin-induced hypoglycaemia.