Abstract
Type 2 diabetes mellitus (DM) has been shown to increase the risk for cognitive decline and dementia, such as Alzheimer’s disease (AD) and vascular dementia (VaD). In addition, there may be a dementia subgroup associated with specific DM-related metabolic abnormalities rather than with AD pathology or cerebrovascular diseases. This type of dementia, not showing hypoperfusion in the parietotemporal lobe on SPECT or cerebrovascular lesions on MRI, was characterized by old age, high hemoglobin A1c level, long duration of diabetes, high frequency of insulin therapy, low frequency of apolipoprotein E 4 carrier, less severe medial temporal lobe atrophy, impaired attention and executive function, less impaired word recall, and slow progression of cognitive impairment, and might be referred to as “diabetes-related dementia”. We studied PiB (amyloid) and PBB3 (tau) PET imaging in 20 subjects with diabetes-related dementia to assess amyloid and tau accumulations in the brain. We found that only 40% of subjects showed positive PiB, whereas 91% showed positive PBB3. Some patients showed PBB3 accumulation restricted to the medial temporal lobe, while some showed PBB3 accumulation in the widespread cerebral cortices beyond the medial temporal lobe in the negative PiB, indicating tauopathy. We concluded that diabetes-related dementia may be more associated with tau pathology rather than amyloid pathology, and with non-specific neuronal injury due to DM-related metabolic abnormalities.