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.
Cell death occurs in the ventral part of the pars compacta, with up to 70% of the cells affected by the time the patient dies of PD.
Cells accumulate abnormal protein alpha-synuclein bound to ubiquitin and are damaged.
This protein accumulation forms inclusions called Lewy bodies.
The hypothesis is Lewy Bodies enter body via the nose or gastrointestinal system and travels to the central nervous system (CNS).
Lewy bodies are present in the enteric and peripheral nervous systems.
The Lewy body selectively travels through the CNS, targeting thin and largely unmyelinated neurons.
Braak system stages disease progression.
This system is divided into six different stages.
The type and severity of symptoms is correlated to progression through the Braak stages.
Early stages are characterized by non-motor symptoms, such as a lessened sense of smell or constipation.
Motor symptoms are often displayed around the mid-stage state, and cognitive symptoms arise as later Braak stages are reached.
Braak suggests that the disease begins in the enteric nervous system and gains entry to the CNS through the vagus nerve.
Stage 1
The disease begins in structures of the lower brainstem and the olfactory system, the dorsal motor nucleus of the vagus nerve in the medulla oblongata and anterior olfactory nucleus are affected.
Lewy neurites, alpha-synuclein aggregates, are more prevalent than globular Lewy bodies in this stage.
Stage 2
In addition to the pathology observed in Stage 1, Stage 2 is characterized by additional lesions in the raphe nuclei and gigantocellular reticular nucleus of the medulla oblongata.
The disease then moves up the brainstem, traveling from the medullary structures to the locus ceruleus in the pontine tegmentum.
Similar to Stage 1, Lewy neurites outnumber Lewy bodies in stage 2 disease.
Stage 3
With Stage 3, the disease has enters the substantia nigra and Lewy body lesions begin to form in the pars compacta.
The latter half of stage 2 involves disease progression into the basal nucleus of Meynert.
The basal nucleus of Meynert is a cluster of acetylcholine-rich neurons in the basal forebrain.
Structures affected in Stages 1 and 2 begin to develop more Lewy bodies.
Stage 4
Stage 4 is characterized by severe dopaminergic cell destruction in the pars compacta, mesocortex and allocortex involvement, amygdala, subnuclei of the thalamus, and anterior olfactory nucleus.
Stage 5
The disease has started to invade the neocortex and spreads into the structures of the temporal, parietal, and frontal lobes.
Cell death can be observed in the substantia nigra, the dorsal motor nucleus of the vagus nerve, the gigantocellular reticular nucleus, and the locus ceruleus.
Stage 6
The disease has fully invaded the neocortex, affecting the motor and sensory areas in the brain. The disease is at its most severe.
Staging in Alzheimer’s disease
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.