While NFT frequency is reportedly reduced in AD+DLB, we often encounter abundant neocortical NFTs in such cases and decided to investigate this discrepancy. Objective: To compare neurofibrillary tangle (NFT) fre-quencyinAlzheimerdiseasewithconcomitantdementiawith Lewy bodies (AD+DLB) with NFT frequency in "pure" AD. Methods: Neurofibrillary tangle frequency, as well as regional staging of neurofibrillary degeneration modified from Braak, was scored in 160 autopsy cases of primary dementia (80

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... +DLB cases and 80 pure AD cases). Results: Neurofibrillary tangle and modified Braak scores were lower in AD+DLB, as reported previously. Yet, neo-cortical NFT scores assumed markedly different patterns in the 2 groups (P = .001). In pure AD, NFT scores of "frequent" were predominant: more cases exhibited frequent than moderate or sparse NFTs. In AD+DLB, the distribution of NFT scores was bimodal: NFTs were either frequent or few to absent. Neocortical NFT scores in the AD+DLB group tended to parallel the severity of other types of tau cytopathology (neuropil threads and tau-positive plaque neurites). Conclusions: Cases of AD+DLB may be divided into 2 subgroups based on the extent of neocortical neurofibrillary pathology. These findings could have implications for disease pathogenesis and treatment.