Endocrine Abstracts

Introduction: According to the literature, the CRH test has the highest specificity in excluding ECS (ACTH 93.9%, cortisol 89.4%). A combination of the high dose dexamethasone test (HDDST) and CRH/desmopressin test (CRH/desmopressinT) is used to increase the discriminatory capacity in ACTH-dependent CS.

Objectives: This study aims to investigate the response to dynamic tests in ECS patients.

Methods: 35 consecutive ECS patients were analyzed (3 SCLC patients were excluded from further analysis). Neuroendocrine tumor (NET) constituted 47% of all EAS (60% gastroenteropancreatic, 40% thoracic (1 thymic and 5 pulmonary carcinoids (PC)), 4 cases were occult. The cut-off points for CRH/desmopressinT was >20% increase in cortisol concentration (Δcortisol%), >35% increase in ACTH (ΔACTH%) and for HDDST >50% decrease of cortisol (-Δcortisol%). The CRH/desmopressinT was performed in 18/32 (16 CRH/2desmopressin), HDDST in 25/32 patients.

Results: All patients responded to CRH/desmopressin (ACTH surge range: 12-197%), with average increase of cortisol and ACTH by 25.5% and 63%. The CRH/desmopressinT ΔACTH% and Δcortisol% were observed in 50% patients, in all PC and in 35.7% of other ECSs (P=0.02). The average percentage increase of ACTH in the CRH/desmopressinT was higher in the PC compared to other ECSs (98% vs 32% P=0.08). In HDDST -Δcortisol% was observed in 3 patients/12% (uterus clear cell carcinoma, PC and occult origin), 28% of the patients responded with a >30% decrease in cortisol. Positive results in both tests, indicative of Cushing’s disease was observed in two ECSs (PC, occult). Patients with ΔACTH%, compared to the remaining ECSs, were characterized by a significantly higher potassium concentration (3.69 vs 2.51 mmol P=0.02) and a higher baseline ACTH concentration (281 vs 214 pg/ml). Patients with -Δcortisol% in HDDST also had higher potassium concentration compared to the non-inhibition group (4.3 mmol/l vs 2.91 mmol/l, P=0.04). There were no significant differences in response to dynamic tests between men and women. There was a strong correlation between the increase in cortisol in the CRH/desmopressinT and the decrease in cortisol in the HDDST (Spearman’s correlation coefficient -0.89 P<0.05).

Conclusion: Half of ECS patients have Δcortisol% and ΔACTH% in CRH/desmopressinT and nearly one third in HDDST have cortisol decrease >30%. Our results also suggest that an increase in cortisol in the CRH/desmopressinT is associated with a decrease in cortisol in the HDDST. Further, multicenter studies are needed to understand the response of ECS patients to dynamic tests and to establish/improve diagnostic differential criteria.