Screening for Cushing’s syndrome in obese type 2 diabetic patients and the predictive factors on the degree of serum cortisol suppression

The aim of this study was to examine the frequency of Cushing’s syndrome (CS) in obese type 2 diabetic patients devoid of specific clinical symptoms of Cushing’s syndrome. A total of 148 obese (BMI ≥30 kg/m² ) type 2 diabetic patients (113 female, 35 male) were included in the study. An overnight 1-mg dexamethasone suppression test (DST) was performed on all patients. Suppression of serum cortisol to <1.8 μg/dL after administration of 1 mg dexamethasone was considered normal suppression. Low dose dexamethasone suppression test was performed on the patients who had serum cortisol level over 1.8 μg/dL after overnight 1 mg DST. Regression analysis was applied to determine the effective factors on suppression of serum cortisol. Mean age, BMI and HbA1c levels respectively were 50,82 ± 8,50 year, 31,78 ± 4,66 kg/m², %8,96 ± 2,42 in males and 54,15 ± 10,348 year, 34,32 ± 5.71 kg/m², % 8,18 ± 2,06 in females. Serum cortisol level was found 1.64 ± 5.62 μg/dl after overnight DST. A total of 9 (6.2 %) patients had non-suppressible overnight DST. Only four (2.6 %) of these patients were diagnosed with Cushing Syndrome after low-dose DST. Diagnosis was confirmed pathologically. Etiologic reasons for Cushing’s syndrome were pituitary microadenoma (2 patients) and adrenocortical adenoma (2 patients). Age and duration of diabetes was found to be related to the degree of suppression. Cushing’s syndrome should be investigated in high-risk groups like uncontrolled diabetes, obesity. All the related factors on the degree of suppression must be considered for the final diagnosis.