OBJECTIVE: To investigate the prevalence and incidence of dementia in patients with non-overtly functional adrenal tumours (NOFATs). DESIGN: A national retrospective register-based study was conducted on patients diagnosed with NOFAT and controls diagnosed between 2005 and 2019, in Sweden. Individuals diagnosed with overt adrenal hormone excess or previous malignancies were excluded. Sensitivity analyses were performed in subgroups with a combination of gallbladder/biliary tract/pancreatic disease. and acute appendicitis, as well as 3- and 12-months of malignancy-free survival. MEASUREMENTS: Prevalence and incidence of dementia. The secondary outcomes were Alzheimer's disease and vascular dementia. RESULTS: Among 20,390 cases, 12,120 (59.4%) were women, and the median (IQR) age was 66 (57-73) years. Among the 125,392 controls, 69,994 (55.8%) were women and the median (IQR) age was 66 (57-73) years. Patients with NOFATs had a lower prevalence of dementia compared to controls (odds ratio [OR] 0.58, 95% CI 0.50-0.68, adjusted OR [aOR] 0.47, 95% CI 0.40-0.56). During the follow-up period (median 4.9 years, IQR 2.2-8.2), incidence of dementia was similar in NOFATs and controls (hazard ratio [HR] 1.05, 95% CI 0.97-1.15, adjusted HR [aHR] 1.06, 95% CI 0.97-1.15). Similar results obtained for Alzheimer's dementia (aOR 0.44, 95% CI 0.34-0.57
aHR 0.94, 95% CI 0.80-1.10) and vascular dementia (OR 0.71, 95% CI 0.52-0.94, aOR 0.48, 95% CI 0.35-0.64
HR 1.29, 95% CI 1.08-1.53, aHR 1.13, 95% CI 0.95-1.35) as well as in the sensitivity analyses. Adrenalectomy did not change the results. CONCLUSION: NOFAT was not associated with an increased risk of dementia.