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Braak H, et al. Neuropathological stageing of Alzheimer-related changes. Acta Neuropathol. 1991;82:239-59. PMID 1759558

One-paragraph summary

Eighty-three autopsy brains from demented and non-demented individuals were examined for extracellular amyloid deposits and intraneuronal neurofibrillary changes. The distribution pattern and packing density of amyloid deposits turned out to be of limited significance for differentiating neuropathological stages. Neurofibrillary tangles and neuropil threads, by contrast, showed a characteristic distribution permitting six stages: transentorhinal stages I–II (mild or severe alteration of transentorhinal layer Pre-α), limbic stages III–IV (conspicuous affection of layer Pre-α in both transentorhinal and proper entorhinal cortex, plus mild involvement of the first Ammon's horn sector), and isocortical stages V–VI (destruction of virtually all isocortical association areas). The authors noted that recognising the six stages required qualitative evaluation of only a few key preparations (PMID 1759558).

Key findings

  • Six-stage tangle scheme: transentorhinal (I–II) → limbic (III–IV) → isocortical (V–VI).
  • Amyloid distribution and packing density had limited value for stage differentiation.
  • Neuritic plaque distribution varied widely both within architectonic units and between individuals; tangles and neuropil threads did not.
  • Staging is achievable from a small number of standard preparations, which is why the scheme became universally adoptable.

Limitations

  • Cross-sectional autopsy material; stage order is inferred from distribution, not observed longitudinally in individuals.
  • Pre-immunohistochemical-standardisation era; modern protocols (silver methods vs p-tau immunostaining) differ in sensitivity.
  • The scheme captures topography, not density. Quantitative work three decades later showed neocortical p-tau burden ranging from 0.2% to 53.7% within Braak stage V, with burden independently predicting cognitive outcome (Richardson 2026, PMID 42184025).
  • Tau-PET data show four distinct spatiotemporal trajectories with prevalences of 18–33%, so the stereotyped sequence describes an average rather than every individual (Vogel 2021, PMID 33927414).

Why it matters

Braak staging is the reason tau, not amyloid, became the pathological staging axis of Alzheimer's disease. It supplies the "B" of the NIA-AA ABC neuropathologic score (Montine 2012, PMID 22101365), the reference standard against which tau-PET was validated (Fleisher 2020, PMID 32338734), and the anatomical vocabulary in which every subsequent propagation model is expressed. Its central empirical claim — that amyloid distribution does not stage the disease while tangle distribution does — anticipated by two decades the finding that cognitive severity correlates best with neocortical tangle burden (Nelson 2012, PMID 22487856).

Cited by wiki pages

  • tau biology and spread
  • imaging and neuropathology