Determination of CUT-off value of 2 days 2MG dexamethasone suppression test in A single center patients with cushing syndrome

Aim: Cushing Syndrome (CS) is a rare disease that causes significant morbidity and mortality if not treated. In this study, we aimed to evaluate the demographic, clinical and laboratory features of CS patients, and to compare the values of dexamethasone suppression tests (DST) used for screening and diagnosis in different etiologies. It was also aimed to determine whether low-dose DST, which is used as a diagnostic test for CS in daily practice, has different cut-off values that will contribute to the determination of the etiology. Materials and Methods: A total of 46 patients with CS who were hospitalized in our hospital between 2015-2018 were evaluated retrospectively. The control group consisted of 21 patients with similar comorbid diseases (diabetes mellitus (DM) and / or hypertension (HT)) without adrenal and pituitary mass. Demographic and clinical characteristics of the patients, laboratory findings, test results used in screening and diagnosis for CS, imaging methods, whether or not surgery was performed, pathology results and etiology of patients who underwent surgical treatment were recorded. Results: 35 (76.1%) out of the 46 patients with CS and 16 (76.2%) out of the 21 control group patients had female gender (p = 1,000). Age and body mass index of the groups were similar (p>0.05). In the dynamic test results of the patients; the median of plasma cortisol levels after 2 days of 2 mg (low dose) DST was 2.70 μg/dl (min-max: 0.49-26.20 μg/dl), the median of plasma cortisol levels after 8 mg (high dose) DST was 2.40 μg/dl (min- max: 0.40-25.00 μg/dl). The median of plasma cortisol levels after dexamethasone-CRH test was 3.24 μg/dl (min-max: 1.12-35.23 μg/dl), the median of 24-hour urinary free cortisol (UFC) after low dose DST was 13.20 μg/24 hours (4.60-36.00 μg/24 hours). There was no statistically significant difference between the groups in terms of ACTH and DHEA-SO4 levels (p = 0.285 and p = 0.078). It was observed that midnight serum cortisol levels at 23:00 pm was higher in the patient group than in the control group (p = 0.018), and it was observed that the cortisol level at 06:00 am was similar in the two groups (p = 0.091). It was detected that19 patients (51.4%) had a mass in the pituitary and 35 (79.5%) had a mass in the surrenal region. The plasma cortisol levels after 1 mg DST and low dose DST of the patients who underwent operation were similar to those who did not undergo surgery. (p> 0.05). It was found that 1 mg DST was not significant in distinguishing patients with pituitary / adrenal masses from those without (p> 0.05). The cut-off value for low-dose DST was ≥4 μg/dl for the pituitary mass with 62.5% sensitivity (95% GA:38.6%-81.5%) and with 87.5% specificity (95% GA: 64.0% -96.5%), cut-off value were calculated as ≤4 μg/dl for adrenal mass with 81.2% sensitivity (95% GA: 64.7%-91.1%) and 85.7% specificity (95% GA: 48.7% -97.4%). Conclusion: It was seen that low-dose DST was significant in differentiating patients with pituitary and adrenal CS. In addition, the cut-off value for plasma cortisol level after low-dose DST was found to be ≥4 μg/dl for pituitary CS patients and ≤4 μg/dl for patients with adrenal CS. Key words: adrenal mass, cushing's syndrome, dexamethasone suppression test, pituitary mass