Primary age-related tauopathy (PART) is characterized by tau neurofibrillary tangles (NFTs) in the absence of amyloid plaque pathology.In the present study,we analyzed the distribution patterns of phosphorylated 43-kDa TAR DNA-binding protein (pTDP-43) in the brains of patients with PART.Immunohistochemistry and immunofluorescence double-labeling in multiple brain regions was performed on brain tissues from PART,Alzheimer\'s disease (AD),and aging control cases.We examined the regional distribution patterns of pTDP-43 intraneuronal inclusions in PART with Braak NFT stages ＞ 0 and ≤ Ⅳ,and a Thai phase of 0 (no beta-amyloid present).We found four stages which indicated potentially sequential dissemination of pTDP-43 in PART.Stage Ⅰ was characterized by the presence of pTDP-43 lesions in the amygdala,stage Ⅱ by such lesions in the hippocampus,stage Ⅲ by spread of pTDP-43 to the neocortex,and stage Ⅳ by pTDP-43 lesions in the putamen,pallidum,and insular cortex.In general,the distribution pattern of pTDP-43 pathology in PART cases was similar to the early TDP-43 stages reported in AD,but tended to be more restricted to the limbic system.However,there were some differences in the distribution patterns of pTDP-43 between PART and AD,especially in the dentate gyrus of the hippocampus.Positive correlations were found in PART between the Braak NFT stage and the pTDP-43 stage and density.