Endocrine Abstracts

Background: The lack of circadian rhythm is a marker of Cushing’s syndrome (CS). Therefore, salivary cortisol rhythm has been suggested for studies on the hypothalamic–pituitary–adrenal (HPA) axis. Late-night salivary cortisol has been used recently by many centers as a first line diagnostic test for CS, yet its accuracy is still on debate.

Aim: To evaluated the performance of morning and late night salivary cortisol in patients with CS and adrenal incidentaloma (AI).

Patients and methods: We performed a case-control study including asymptomatic patients with AI in whom CS was rule out (with other screening and diagnosis tests) and patients with confirmed CS and analyzed morning (MSC) and late-night salivary cortisol (LNSC) levels and MSC-to-LNSC difference. We assessed the accuracy of LNSC in the CS screening, considering as a cut-off a 0.350 μg/dl, previously validated by our laboratory. Statistical analysis was performed using SPSS v22.0, considering statistical significance at the 0.05 level.

Results: We included 81 patients with AI and 11 patients with CS (ten patients with active Cushing’s disease and one patient with ectopic CS). The majority of patients were female in both groups (61.7% and 81.8%, P=0.167 in AI and CS, respectively), but patients with AI were older than CS patients (66 years, min-máx 38–92 vs 55 years, min-máx 28–75; P<0.05). The LNSC median level was significantly higher in the group of patients with CS (0.634 μg/dl (min-máx 0.192–1.280) vs 0.230 μg/dl (min-máx 0.054–1.140); P<0.001) but no significant differences were found in median MSC levels among the two groups (0.735 μg/dl (min-máx 0.266–2.210) vs 0.506 μg/dl (min-máx 0.054–2.590); P=0.084). The median MSC-to-LNSC difference was 0.740 μg/dl (min-máx −0.46–0.93) in CS patients and 0.322 μg/dl (min-máx −0.78–2.46) in AI patients (P=0.051). LNSC above 0.350 μg/dl achieved a sensibility of 90.9% and a specificity of 77.8% in the diagnosis of CS, with positive and negative predictive values of 35.7% and 98.4%.

Conclusions: In this population, patients with CS presented LNSC levels significantly higher than patients with AI, but MSC levels and the MSC-to-LNSC difference weren’t significantly different between the two groups. The cut-off of 0.350 μg/dl to the LNSC presented a good accuracy with a very high NPV and it’s a useful tool for the diagnosis of CS.