What happens later?
The apraxia and dystonia usually spread to the other arm within two or three years and can affect the legs and feet as well, which can cause unsteady walking. There can be slurring of speech and difficulty swallowing liquids, with coughing and even irritation of the lungs from fluids that drip down. Some people develop difficulty multitasking or organizing their thoughts. Some individuals can lose some behavioral inhibitions.
How common is CBD?
CBD is very rare: about five people per million, which comes to about 1,600 people in the United States, most of whom have not yet been accurately diagnosed. For Parkinson’ s, the figure is 700,000, and for Alzheimer’ s disease, 5.8 million.
How does CBD differ from the more common brain degeneration disorders?
Unlike Parkinson’ s, CBD usually has little tremor. Unlike PSP, CBD has only mild problems with balance and eye movements. However, CBD does have features that these other diseases usually lack, such as apraxia, dystonia, and myoclonus. Unlike all of these other diseases, CBD is highly asymmetric in its limb involvement, meaning that either the right or left limbs start to show problems well before the opposite side and remains the worse side throughout. Parkinson’ s disease is also asymmetric but not to the same degree.
In CBD, some degree of cognitive loss is present in half of individuals at the outset and in 70 % eventually. If it does occur, it does not feature the memory problem that is so apparent in Alzheimer’ s disease. Rather, the dementia of CBD is often characterized by trouble in planning, resisting impulses, and synthesizing information into a new idea. These mental functions are performed mostly by the front part of the brain( the“ frontal lobes”). In Alzheimer’ s, on the other hand, the problem is mostly in the part of the brain just above the ears( the“ temporal lobes”), where memory functions are concentrated. CBD may in some cases also feature difficulty in recalling or understanding words(“ aphasia”), loss of visual-spatial skills, loss of ability to order a complex manual task(“ apraxia”), disinhibited social behavior, and general loss of interest in one’ s problems or in one’ s environment(“ apathy”).
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What happens in the brain?
In people with CBD, some groups of brain cells break down and die off. Central to that process is the abnormal folding and clumping of a protein called tau, which is a normal component of the brain. Its job is to help maintain the microtubules, which are stiff rods that function as the brain cells’ internal transportation and skeletal system. It appears that the cells’ death is caused by the tau protein clumps themselves and not by the reduced availability of tau for its normal function. The clumps’ technical name is neurofibrillary tangles.
We know several reasons why tau might misfold, but we don’ t know which one( s) are relevant to CBD. Tau forms similar aggregates in about a dozen other diseases, including Alzheimer’ s disease, PSP, chronic traumatic encephalopathy( CTE), and about half of all cases of frontotemporal dementia. The specific disease depends on the chemical characteristics of the tau aggregate and which brain cells are involved. We don’ t yet understand what determines these.