Is It Relevant to Screen Subclinical Cushing’s Syndrome in Patients with Type 2 Diabetes Mellitus?

Background: Subclinical Cushing’s syndrome (SCS) is defined as autonomous cortisol secretion in patients devoid of specific clinical symptoms of hypercortisolism, as in the classic CS. However, sustained exposure to chronic slightly elevated cortisol concentrations may result in some classical metabolic complications of CS such as impaired glucose tolerance and diabetes. Currently, the frequency of SCS is widely variable. We have conducted a cross-sectional study to prospectively evaluate the prevalence of SCS among type 2 diabetic (T2D) patients with poor control, and to determine whether systematic screening for SCS in T2D patients is worthwhile. Methods: It was a cross-sectional study including 221 T2D patients referred to the National Institute of Nutrition of Tunis for poor glycemic control (HbA1c >= 8%). The first screening step of SCS was the 1-mg overnight dexamethasone suppression test (ODST) using a revised criterion for cortisol suppression. In the second confirmatory step, patients with abnormal ODST underwent a 48-h, 2-mg low-dose dexamethasone suppression test (LDDST) to confirm the diagnosis. The cut-off for cortisol suppression was 50 nmol/L (1.8 µmol/dL) in the two tests. Results: Thirteen patients (5.9%) failed to suppress cortisol levels less than the cut-off after ODST. SCS was confirmed by LDDST in one patient among them (0.45%). The autonomous cortisol secretion was related to a pituitary adenoma. Our study revealed that the frequency of SCS of 0.45% did not allow performing an analytical study in order to identify predictive factors of SCS among T2D patients. Conclusion: SCS is rare among T2D patients. Systematic screening of SCS in T2D patients with poor glycemic control is not worthwhile. The screening should be performed only in patients with a particular clinical and/or biological context. J Endocrinol Metab. 2017;7(6):178-184 doi: https://doi.org/10.14740/jem454w