Solves some of the initial problems with muscle tremors and control, but does nothing for the dementia that sets in later.
“The average time from onset of movement problems to the development of dementia is about 10 years.”
https://memory.ucsf.edu/dementia/parkinsons/parkinson-diseas....
I've read that exercise, hard exercise, can mitigate or recover some of the effects of parkinsons.
The motor symptoms of Parkinson’s are caused by the loss of dopamine producing neurons in the motor cortex. The loss of those neurons for any reason would cause Parkinson style motor symptoms.
The cause of the loss of dopamine producing neurons in standard Parkinson’s is not understood, but appears to be related to a thing called Lewy bodies which are deposits of a protein called alpha-synuclein. The presence of Lewy bodies outside of the motor cortex is correlated with a disease called Lewy body dementia rather than Parkinson’s.
Most likely, there is a underlying process that causes neuron loss that slowly spreads. This process frequently starts in the motor cortex resulting in Parkinson’s, but sometimes starts elsewhere causing Lewy body dementia. Dementia in a person with Parkinson’s likely occurs when the process starts spreading beyond the motor cortex which effectively causes Lewy body dementia now that it is no longer isolated to the motor cortex.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007714/
It certainly had a significant impact on a Parkinson's patient I knew (from regular expressions of and involvement with delusional hallucinations to relatively normal, organized behavior).
Of course the loss of cells might be self reinforcing.