The continuous 7-hour intravenous dexamethasone suppression test in the differential diagnosis of ACTH-dependent Cushing's syndrome.
OBJECTIVE
A recent report showing disappointingly low sensitivity and specificity for the oral high dose dexamethasone test in the differential diagnosis of Cushing's syndrome prompted us to re-evaluate the results obtained in our centre using the continuous 7-hour intravenous dexamethasone suppression test for this purpose.


METHODS
105 patients with ACTH-dependent Cushing's syndrome were included in this study; 78 with Cushing's disease, 8 with ectopic ACTH-secreting tumours and 19 were classified as 'of unknown aetiology'.


RESULTS
In 74/78 (94.9%) of patients with Cushing's disease and in 3/8 (37.5%) patients with the ectopic ACTH syndrome, a plasma cortisol decrease > 190 nmol/l at 7 h as compared to baseline values was achieved in the continuous 7-hour intravenous dexamethasone suppression test. Using a plasma cortisol decrease > 190 nmol/l at 7 h as compared to baseline values as the cut-off value, the sensitivity and specificity of the continuous 7-hour intravenous dexamethasone suppression test for the diagnosis of Cushing's disease in patients with ACTH-dependent Cushing's syndrome were 94.9% and 62.5%, respectively.


CONCLUSIONS
In patients with ACTH-dependent Cushing's syndrome with a plasma cortisol decrease > 190 nmol/l at 7 h in the continuous 7-hour intravenous dexamethasone suppression test, additional localizing investigations such as bilateral simultaneous inferior petrosal sinus sampling and/or pentetreotide scintigraphy should be performed when no clearly discernible pituitary adenoma is observed on MRI studies. Patients with ACTH-dependent Cushing's syndrome with a plasma cortisol decrease < 190 nmol/l at 7 h in the continuous 7-hour intravenous dexamethasone suppression test should also undergo bilateral simultaneous inferior petrosal sinus sampling and/or pentetreotide scintigraphy to demonstrate the presence of a nonpituitary source of ACTH overproduction.
van den Bogaert
D P
DP
Department of Internal Medicine III, University Hospital Rotterdam, The Netherlands.
de Herder
W W
WW
de Jong
F H
FH
Biemond
P
P
van der Lely
A J
AJ
Lamberts
S W
SW
D000182:ACTH Syndrome, Ectopic / Q000097:blood / Q000175:diagnosis; D000304:Adrenal Cortex Function Tests; D003480:Cushing Syndrome / Q000097:blood / Q000175:diagnosis*; D003907:Dexamethasone; D003937:Diagnosis, Differential; D005938:Glucocorticoids; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007262:Infusions, Intravenous; D011237:Predictive Value of Tests
D005938:Glucocorticoids; D003907:Dexamethasone; D006854:Hydrocortisone