DETERMINING THE EXTENT OF ALZHEIMER’S DISEASE WITH BRAAK STAGING

Normally, tau protein is used by the brain's neurons as a kind of "scaffolding." But for reasons that are still unclear, as people age the tau protein starts to aggregate into filaments inside the neurons. These tau filaments soon grow out of control, eventually forming distinctive tau tangles. They fill up the neurons and cause them to burst. At this point, neuron death is unstoppable.

Braak staging - developed by German pathologist Heiko Braak - is a way to measure the severity of Alzheimer's disease based on how many tau tangles there are in the brain, and where they are, based on brain autopsy. 

Braak Stage 1 - Braak stage 1 is the point at which tau protein starts to clump into tau tangles. In stage 1 there are no external symptoms and it might take many years before there is noticeable dementia. Nearly everyone will reach Braak stage 1 between 40 and 90 years of age. About 30 percent of 50-year-olds will reach Braak stage 1.

Braak Stage 2 - Tau tangles have accumulated further and have caused some neurons to burst apart and die. Mental testing reveals minimal impairment. Tau tangles at this are found in the brains of about 60 percent of people over age 65. 

Braak Stage 3 - Tau tangles and neuronal death have likely caused some memory impairment, but only about 10 percent of patients will be diagnosed as suffering from dementia. About 45 percent of 80-year-olds have reached this stage. 

Braak Stage 4 - Tau tangles are beginning to form in the outer layers of the cerebral cortex. The patient is experiencing significant impairments in memory and other aspects of cognitive function. 70 percent of patients with this level of tau tangles in the brain will be diagnosed with dementia.

Braak Stage 5 - Tau tangles have caused extensive neuronal death, giving rise to severe memory and cognitive impairment. They are beginning to involve deep areas of the brain that control the initiation of movement. About 80 percent of patients with this level of tangles will be diagnosed with moderate to severe dementia.

Braak Stage 6 - Tau tangles have formed extensively throughout the brain and have caused extensive neuronal death. The outer layers of the brain that integrate activities and the deep areas of the brain that control movement are filled with tau tangles. All patients with this many tau tangles in the brain will be diagnosed as suffering from severe dementia. They will be completely unable to care for themselves and will have difficulty recognizing family members

(Source:  John Hopkins Health Alert, Memory on 29 July 2013)