Lower Insulin Secretion Is Associated with Hippocampal and Parahippocampal Gyrus Atrophy in Elderly Patients with Type 2 Diabetes Mellitus.

Aims/introduction We aimed to examine the association between diabetes-related parameters and hippocampal and parahippocampal gyrus atrophy (HPGA) in patients with type 2 diabetes mellitus (T2DM) to elucidate the risk factors for HPGA, which is often accompanied by Alzheimer's disease (AD). Materials and methods A total of 137 patients aged ≥ 50 years with T2DM (mean age: 67.8 ± 9.8 years) underwent brain magnetic resonance imaging (MRI) scans and comprehensive health examinations. We measured the volume of interest (VOI)-a portion of the inner temporal lobe that includes the hippocampus, amygdala, and entorhinal cortex (frontal part of the parahippocampal gyrus)-using the voxel-based specific regional analysis system for AD in each patient. The diabetes-related parameters included HbA1c, fasting plasma glucose (FPG), C-peptide (CPR) index (serum CPR/FPG x 100), and duration of diabetes. Results The mean HbA1c was 9.3 ± 2.2 %, the median CPR index (interquartile range) was 1.29 (0.85-1.74), and the median duration of diabetes was 10 years (interquartile range: 3-20 years). The severity score of VOI atrophy was more than 1.0 in 36 patients. Using multivariate logistic regression analysis, we found that age (OR=1.09, 95% CI=1.02-1.15) and CPR index (OR=0.451, 95% CI=0.216-0.940) were significantly associated with HPGA. Conclusions Lower insulin secretion was significantly associated with HPGA in patients with T2DM. The results of this study support the hypothesis that insulin-signaling abnormalities are involved in the pathophysiology of AD.