Why don’t all the symptoms get better at once?
Sometimes the people who care for those with Alzheimer’s disease are surprised at how some symptoms can show so much improvement, while others seem to be staying the same or getting worse. How symptoms work in Alzheimer’s disease is complicated. While it is generally true that a lot of symptoms come about because of a decrease in the brain chemical acetylcholine, not all of the symptoms do. Because of this, there are some symptoms which simply will not respond to changes in acetylcholine. Of course the situation is more complex. The brain can adapt and get used to having lower levels of acetylcholine. When a drug is introduced to raise the level of acetylcholine, the brain then has to adapt all over again to the new increase amount of neurotransmitter.
A striking example of this is sometimes seen in patients who have dementia with Lewy bodies. In dementia with Lewy bodies, people have a mixture of low acetylcholine and low dopamine. Dopamine in Parkinson’s disease and other types of Parkinsonism In some people with Lewy body dementia, giving a drug that increases the amount of acetylcholine actually makes their Parkinsonism worse. This is because Parkinsonism sometimes comes about not just as a result of the absolute amount of dopamine, but the amount of dopamine in relation to acetylcholine. Thus, increasing the acetylcholine has an effect similar to lowering the amount of dopamine. Puzzlingly however, the response in dementia with Lewy bodies is very variable, so that in some people Parkinsonism gets better and in others Parkinsonism gets worse.