Time-dependent Increase in Cortisol after 1-mg Overnight Dexamethasone Suppression Test in Adrenal Incidentalomas

Guidelines recommend the 1-mg overnight dexamethasone suppression test (ODST) for diagnosing mild autonomous cortisol secretion (MACS) in adrenal incidentalomas (AI). Age may influence cortisol levels after 1-mg ODST (post-ODST cortisol levels). This study investigated changes in post-ODST cortisol levels over time in Korean patients with AI.

This retrospective, multicenter cohort study included 1063 patients with AI from 4 tertiary hospitals between 2003 and 2022. Post-ODST cortisol changes were evaluated using the ODST ratio (last to baseline measurement). A generalized additive model assessed the association between age and post-ODST cortisol levels. Multivariable logistic regression estimated odds ratios (OR) for post-ODST cortisol progression by follow-up duration.

The ODST ratio increased with follow-up duration (β = .063, P < .001). Least-square mean ± SE of the ODST ratio was higher in the 2- to 5-year (1.20 ± 0.02, P < .001) and >5-year groups (1.66 ± 0.06, P < .001) than in the <2-year group (1.12 ± 0.03). Age showed a significant nonlinear effect on post-ODST cortisol levels (P < .001). The risk of post-ODST cortisol progression was higher in the >5-year group than in the <2-year group for nonfunctioning AI [OR = 5.44, 95% confidence interval (CI) = 2.90-10.23, P < .001] and MACS (OR = 3.86, 95% CI = 1.19-12.46, P = .024).

Cortisol levels after 1-mg ODST increased over time, suggesting an age-related effect and highlighting the need for age-tailored diagnostic and management strategies for MACS in older patients with AI.