We recommend a new term, “primary age-related tauopathy” (PART), to describe a pathology that is commonly observed in the brains of aged individuals. Many autopsy studies have reported brains with neurofibrillary tangles (NFT) that are indistinguishable from those of Alzheimer's disease (AD), in the absence of amyloid (Aβ) plaques. For these “NFT+/Aβ−” brains, for which formal criteria for AD neuropathologic changes are not met, the NFT are mostly restricted to structures in the medial temporal lobe, basal forebrain, brainstem, and olfactory areas (bulb and cortex). Symptoms in persons with PART usually range from normal to amnestic cognitive changes, with only a minority exhibiting profound impairment. Because cognitive impairment is often mild, existing clinicopathologic designations, such as “tangle-only dementia” and “tangle-predominant senile dementia”, are imprecise and not appropriate for most subjects. PART is almost universally detectable at autopsy among elderly individuals, yet this pathological process cannot be specifically identified pre-mortem at the present time. Improved biomarkers and tau imaging may enable diagnosis of PART in clinical settings in the future. Indeed, recent studies have identified a common biomarker profile consisting of temporal lobe atrophy and tauopathy without evidence of Aβ accumulation. For both researchers and clinicians, a revised nomenclature will raise awareness of this extremely common pathologic change while providing a conceptual foundation for future studies. Prior reports that have elucidated features of the pathologic entity we refer to as PART are discussed, and working neuropathological diagnostic criteria are proposed.

Nelson et al. describe a recently recognized brain disorder that mimics the clinical features of Alzheimer’s disease: L imbic-predominant A ge-related T DP-43 E ncephalopathy (LATE). They review the literature and present consensus-based recommendations of an international, multidisciplinary working group, providing guidelines for diagnosis and staging of LATE neuropathological changes.

Objective Neurofibrillary pathology has a stereotypic progression in Alzheimer's disease (AD) that is encapsulated in the Braak staging scheme. Some AD cases do not fit the Braak staging scheme and are considered atypical. The purpose of this study was to compare clinical and pathological features of typical AD with atypical AD that had either hippocampal sparing (HpSp) and limbic-predominant (LP) neurofibrillary pathology. Methods A mathematical algorithm was devised to classify AD cases into typical, HpSp and LP according to the density and distribution of neurofibrillary tangle (NFT) counts from thioflavin S fluorescent microscopy in three cortical regions and two Hp sectors. The algorithm was applied to NFT counts of 889 cases of AD (409 men and 480 women; age at death: 37-103 years). Cases so classified were compared on clinical, demographic, pathological and genetic grounds. An independent series of 113 cases of AD were similarly evaluated to validate findings from the initial cohort. Findings In comparison to typical AD, HpSp (n=97) had higher NFT densities in cortical areas and lower NFT densities in hippocampus, while LP (n=127) had lower NFT densities in cortical areas and higher NFT densities in the Hp. HpSp had less Hp atrophy than typical AD (11%) and LP (14%). HpSp were younger, with a higher proportion of men, whereas LP was older, with a higher proportion of women. MAPT H1H1 genotype was more frequent in LP compared with HpSp, but not between LP and typical AD. APOE ε4 allele status differed among AD subtypes only when age of onset was considered. Clinical presentation, age of onset, disease duration, and rate of decline differed among the AD subtypes. The findings were confirmed in a replication cohort. Interpretation Our data supports the hypothesis of distinct clinicopathologic subtypes of AD. HpSp and LP AD account for about 25% of AD and are important to consider in clinical, genetic, biomarker and treatment studies.

The Dementia with Lewy Bodies (DLB) Consortium has refined its recommendations about the clinical and pathologic diagnosis of DLB, updating the previous report, which has been in widespread use for the last decade. The revised DLB consensus criteria now distinguish clearly between clinical features and diagnostic biomarkers, and give guidance about optimal methods to establish and interpret these. Substantial new information has been incorporated about previously reported aspects of DLB, with increased diagnostic weighting given to REM sleep behavior disorder and 123iodine-metaiodobenzylguanidine (MIBG) myocardial scintigraphy. The diagnostic role of other neuroimaging, electrophysiologic, and laboratory investigations is also described. Minor modifications to pathologic methods and criteria are recommended to take account of Alzheimer disease neuropathologic change, to add previously omitted Lewy-related pathology categories, and to include assessments for substantia nigra neuronal loss. Recommendations about clinical management are largely based upon expert opinion since randomized controlled trials in DLB are few. Substantial progress has been made since the previous report in the detection and recognition of DLB as a common and important clinical disorder. During that period it has been incorporated into DSM-5, as major neurocognitive disorder with Lewy bodies. There remains a pressing need to understand the underlying neurobiology and pathophysiology of DLB, to develop and deliver clinical trials with both symptomatic and disease-modifying agents, and to help patients and carers worldwide to inform themselves about the disease, its prognosis, best available treatments, ongoing research, and how to get adequate support.