Abstract
In this study, we compared the 2 mg dexamethasone suppression test (DST) with the
gold-standard 1 mg DST in obese patients in order to reduce the false-positive rate
for Cushing’s syndrome (CS). The primary endpoint was the comparison of serum cortisol
levels after 1 mg versus 2 mg DST in patients with a BMI >30 kg/m2 and at least one additional feature of the metabolic syndrome. Secondary endpoints
were comparison of salivary cortisol and ACTH levels, respectively. Fifty-four obese
patients were included. Median serum cortisol levels after 1 mg DST and 2 mg DST were
similar [28 nmol/l (20; 36) vs. 28 nmol/l (20; 38), p=0.53]. Salivary cortisol was
8.2 nmol/l (4.7; 11.7) after the 1 mg DST vs. 6.7 nmol/l (4.2; 9.5) after the 2 mg
test, p=0.09. ACTH levels were higher after the 1 mg DST compared to the 2 mg DST
[10.0 pg/ml (7.6; 10.7) vs. 5.0 pg/ml (5.0; 5.1), p<0.0001]. The false positive rate
after the 1 mg DST was 14.8% (n=8) and was reduced to 11.1% (n=6) after the 2 mg DST.
All non-suppressors (n=8) had type 2 diabetes and most of them took a medication interacting
with cytochrome P450 3A4 (CYP3A4). In individuals with obesity, the 2 mg DST was not
superior to the 1 mg DST in regard to serum cortisol levels. However, in some patients,
particularly with poorly controlled diabetes or medication interacting with CYP3A4
and without adequate suppression after the 1 mg DST, the 2 mg DST might prove helpful
to reduce the false-positive rate for CS.
ClinicalTrials.gov Number: NCT02227420
Key words
metabolic syndrome - obesity - dexamethasone suppression test - Cushing’s syndrome
