The Relationship Between Bone Health Status of Post-Menopausal Women with Non-Functional Adrenal Tumours/Mild Autonomous Cortisol Secretion and Their Baseline Morning Adrenocorticotropic Level

<b>Background</b>. Glucocorticoid-induced osteoporosis represents a well-known type of secondary osteoporosis (SOp). While the most prevalent sub-category includes corticotherapy, another important contributor is represented by Cushing's syndrome. In this traditional landscape, adrenal incidentalomas do not involve a standard cause of SOp, since most of them are non-functioning adrenal tumours (NFATs). Yet, 30-40% of them are not entirely "non-functioning", due to mild autonomous cortisol secretion (MACS). Despite not being a guideline-based diagnosis, a lower ACTH might point to various NFATs/MACS complications. <b>Objective</b>. This study aimed to determine the relationship between the bone health status of post-menopausal women with NFATs/MACS and their baseline morning ACTH level. The bone health indicators were DXA, FRAX, and bone remodelling markers. <b>Methods</b>. This was a retrospective, real-life, transversal study in adult females who were hospitalized in a single tertiary centre of endocrinology. They were all anti-osteoporotic drug-naïve. The subjects underwent CT and DXA scanning and a 1 mg dexamethasone suppression test (DST). <b>Results</b>. The cohort (sample size of N = 84 patients, 61.49 ± 7.86 years) had a type 2 diabetes rate of 18%, arterial hypertension rate of 75%, and a dyslipidemia rate of 78%. Median ACTH was 11.89 pg/mL. The prevalence of MACS was 30.95%. The mean largest tumour diameter (LTD) was 2.25 ± 0.99 cm. ACTH correlated with second-day cortisol after the 1 mg DST (r = -0.301, <i>p</i> = 0.024), and LTD (r = -0.434, <i>p</i> < 0.001). ROC analysis for the bone resorption marker CrossLaps showed an AUC of 0.647 (<i>p</i> = 0.05), with the highest Youden index for the cut-off at 0.32 ng/mL (sensitivity 87.50%, specificity 39.50%). Bone impairment (osteoporosis + osteopenia) was found in 65% of patients, with an osteoporotic fracture prevalence of 4.76%. The lowest mean T-score (-1.12 ± 1.00) showed osteopenia, and the median trabecular bone score pointed a partially degraded microarchitecture [median (interquartile interval): 1.320 (1.230, 1.392)]. FRAX and FRAXplus estimations correlated with bone mineral density (BMD) at all three central DXA sites, regardless of the ACTH cut-off. Patients with a low ACTH (<10 pg/mL) displayed similar bone/adrenal features when compared to those with normal ACTH, except forbut they had a higher MACS rate (45.45% versus 21.57%, <i>p</i> = 0.021) and a larger LTD (2.67 ± 0.98 versus 1.98 ± 0.92 cm, <i>p</i> = 0.003). Fracture estimation showed that only in patients with a low ACTH, the 10-year fracture risk for major osteoporotic fractures (MOF) adjusted for lumbar BMD was lower than the risk for MOF adjusted for diabetes (<i>p</i> = 0.036), and the 10-year hip fracture risk was lower when adjusted for lumbar BMD (<i>p</i> = 0.007). ACTH correlated with lumbar BMD (r = 0.591, <i>p</i> = 0.002) only in the group with an ACTH < 10 pg/mL, suggesting its potential usefulness as a bone biomarker in these cases. On the other hand, MACS-negative subjects with a low ACTH versus those with a normal ACTH showed higher CrossLaps (0.60 ± 0.27 versus 0.42 ± 0.21 ng/mL, <i>p</i> = 0.022), indicating an elevated bone resorption even in patients with tumours that are regarded as true non-secretors. <b>Conclusions</b>. A subgroup of patients diagnosed with NFATs/MACS might be prone to skeletal damage, and biomarkers such as ACTH (specifically, suppressed ACTH) might serve as a surrogate pointer to help refine this higher risk in daily practice. Further research to address other ACTH cut-offs will place ACTH assays in the overall bone status evaluation in these patients, most probably not as a single biomarker, but in addition to other assays.