Amyloid-negative dementia in the elderly is associated with high accumulation of tau in the temporal lobes

Background: We previously reported that among cases clinically diagnosed with Alzheimer’s disease, the proportion of amyloid beta (Aβ) -negative case increases in the elderly population. Tauopathy including Argyrophilic Grain Disease (AGD) and Neurofibrillary Tangle-Predominant Dementia (NFTPD), may be the leading causes of such dementia. Objective: To evaluate the involvement of tau, we studied tau accumulation in Amyloid-Negative Dementia Cases in the Elderly (ANDE) with Positron Emission Tomography (PET). Methods: Seven cases with slowly progressive dementia who were older than 80 years and were negative for Aβ were studied. In one case, autopsy obtained 2 years after the PET examination revealed neurofibrillary tangles limited around the parahippocampal gyrus. Four cases showed strong laterality in magnetic resonance imaging atrophy (clinical AGD), while the other three cases had no significant laterality in atrophy (clinical NFTPD). Agecorrected PET data of healthy controls (HC; n = 12) were used as control. Tau accumulation was evaluated with [¹¹C]PBB3-PET. Results: High accumulation was found in the lateral temporal cortex in ANDE. In autopsy case, scattered neurofibrillary tangles were found in the parahippocampal gyrus. In addition, there was a very high accumulation of PBB3 in the large area of bilateral parietal lobes, although no corresponding tau component was found in the autopsied case. Conclusion: Relatively high burden of tau deposition was commonly observed in the lateral temporal cortex and parietal cortex of ANDE, part of which may explain dementia in these subjects. [¹¹C]PBB3 may be useful in detecting tauopathy in ANDE.