The role of combined low-dose dexamethasone suppression test and desmopressin stimulation test in the diagnosis of persistent Cushing's disease. Case report.

Cushing's disease is related to a significant increase in mortality due to chronic hypercortisolaemia complications. It is known that 50% of non-treated subjects die within 5 years. Transsphenoidal selective adenomectomy is the treatment of choice. The incidence of relapses, even following a successful surgical procedure, is high and reaches 20-25% during the 5-year follow-up period. The authors discuss the case of a patient, currently aged 60, after repeat pituitary surgery, with progressive cardiovascular complications, in whom persistent Cushing's disease was diagnosed. The diagnosis was determined despite normal plasma ACTH, serum cortisol levels, and 17-OHCS concentrations in daily urine. There was also a lack of obvious pituitary adenoma features in the magnetic resonance imaging (MRI). Persistent Cushing's disease was diagnosed based on the combined dexamethasone desmopressin test. The presented case points to the role of provocative testing, including the desmopressin test following 1 mg of dexamethasone, for diagnostically difficult cases of Cushing's disease.