He had Parkinson's disease which is a progressive neurological disorder. It is marked by rotary tremors of the hands and arms and by a masklike facial expression. It can cause depression and dementia in some people. He lost his ability to walk and speak clearly because Parkinson's is caused by damage to the substantia nigra region of the brain. This, in turn, causes a lack of dopamine which can be treated by taking L-dopa but this is only a temporary cure. Death occurs after 10-20 years because immobility and difficulty in coordination can cause choking(as happened to the Pope) or can cause the person to fall. Pope John Paul died due to septic shock brought on by a UTI. He was tube fed at the end because of the tracheostomy.