Braak staging refers to two methods used to classify the degree of pathology in Parkinson's disease and Alzheimer's disease. These methods are used both in research and for the clinical diagnosis of these diseases and are obtained by performing an autopsy of the brain.
The main pathological characteristic of Parkinson's Disease is cell death in the substantia nigra and more specifically the ventral part of the pars compacta, affecting up to 70% of the cells by the time the patient dies. The mechanisms by which the brain cells are lost are varied. One mechanism consists of an abnormal accumulation of the protein alpha-synuclein bound to ubiquitin in the damaged cells. This protein accumulation forms inclusions called Lewy bodies.
According to the Braak staging Lewy bodies first appear in the olfactory bulb, medulla oblongata and pontine tegmentum, individuals at this stage being asymptomatic. As the disease evolves, Lewy bodies later attain the substantia nigra, areas of the midbrain and basal forebrain, and finally reach areas of the neocortex.
Staging in Alzheimer's disease was described by Braak in 1991.
Braak stages I and II are used when neurofibrillary tangle involvement is confined mainly to the transentorhinal region of the brain, stages III and IV when there is also involvement of limbic regions such as the hippocampus, and V and VI when there is extensive neocortical involvement. This should not be confused with the degree of senile plaque involvement, which progresses differently.
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