Desmopressin test in the diagnosis and follow-up of cyclical Cushing's disease.

OBJECTIVE: To assess the utility of the desmopressin (DDAVP) test in the diagnosis and follow-up of a cyclical Cushing's disease (CCS) case.

MATERIAL AND METHODS: Laboratory tests included morning and midnight serum cortisol levels, 24h urine free cortisol excretion, midnight salivary cortisol levels, serum cortisol levels after low (1 mg) and high (8 mg) dexamethasone, plasma ACTH and serum cortisol levels after DDAVP. Magnetic resonance imaging (MRI) was used to assess the presence of a pituitary adenoma. The resected tumor specimen was studied by histological, immunohistochemical and cell biology techniques.

RESULTS: A patient was referred to our unit with a diagnosis of Cushing's syndrome (CS) for further evaluation and treatment. However, no biochemical evidence of hypercortisolism was observed in the follow-up evaluations. Furthermore, the typical features of CS fluctuated throughout this period. A consistent positive response to the DDAVP stimulation test was observed during the diagnostic work-up, even when overt clinical features of CS were not apparent, raising suspicion for CCS. After two years of follow-up a definitive diagnosis of hypercortisolism was established. An MRI scan revealed a pituitary adenoma, as the source of ACTH production. After transphenoidal surgery, clinical signs of CS resolved and the response to DDAVP became negative. DDAVP induced a significant increase in ACTH levels in cultured pituitary adenoma cells, consistent with the in vivo DDAVP test results.

CONCLUSIONS: Our case illustrates the utility of the DDAVP test in the evaluation of patients with suspected CCS. The DDAVP test could facilitate the management of CCS by shortening the time of diagnosis.