S. Sriussadaporn et al., NOCTURNAL 8MG DEXAMETHASONE SUPPRESSION TEST - A PRACTICAL AND ACCURATE TEST FOR IDENTIFICATION OF THE CAUSE OF ENDOGENOUS CUSHINGS-SYNDROME, British journal of clinical practice, 50(1), 1996, pp. 9-13
The efficacy of a nocturnal 8mg dexamethasone suppression test (noctur
nal DST) was compared with that of the standard high-dose dexamethason
e suppression test (standard DST) in identifying the cause of endogeno
us Cushing's syndrome in 10 proven cases with Cushing's disease, 20 wi
th adrenal tumours, and one with ectopic ACTH syndrome. The nocturnal
test compared serum cortisol concentration at 8am before and after adm
inistration of a single dose of 8mg dexamethasone at 11pm. Suppression
of serum cortisol level to <50% of the baseline value indicated a dia
gnosis of Cushing's disease, while a lack of suppression below that li
mit indicated one of the other two causes of Cushing's syndrome: gluco
corticoid-secreting adrenal tumour or ectopic ACTH syndrome. The noctu
rnal DST had a sensitivity of 90%, a specificity of 100%, an accuracy
of 96.8%, a positive predictive value of 100%, and a negative predicti
ve value of 95.5%. These values are comparable to the efficacy of the
standard DST in distinguishing Cushing's disease from glucocorticoid-s
ecreting adrenocortical tumour or ectopic ACTH syndrome. Furthermore,
this rapid test does not require hospitalisation or urine collection l
ike the standard DST. The nocturnal 8mg dexamethasone suppression test
is practical, fairly reliable, and an effective alternative with whic
h to identify the cause of endogenous Cushing's syndrome.