Parkinsons and Secondary Dementia

My father is 75 years old and was diagnosed with Parkinson's disease in 1991. Up until the month of May he was still walking on his own, however very slowly and with a tendency to fall often. During May and June his condition worsened considerably at a horrifying pace. In June he was completely bedridden and contracted pneumonia for which he spent nearly a month in the hospital and then undergoing rehab. During this time it was clear to us that the parkinsons had progressed to a point that prevented him from swallowing properly (the pnueomnia was caused by aspirated food that he could not swallow) and he underwent a procedure for a stomach feeding tube. This has been a positive thing so far as now he has recovered significantly and has days where his mental clarity is superior to that of the last few years.

He has a tendency to have his bad days in which he regularly speaks to people who do not exist, and cannot grasp simple concepts or even answer a simple yes or no question properly. His cognitive abilities, speech and processing, have detoriated, and he was even misdiagnosed with alzheimers disease several years earlier. The current diagnosis is that he suffers obviously from PD with secondary dementia.

My question is do most Parkinson's patients tend to develop a type of dementia in which cognitive and reasoning abilities are completely obliterated? How does this dementia usually come about? And most importantly, is there anything that can be done short of brain implants?

He currently takes Sinemet for Parkinsons as well as Aricept and Nameda for the dementia.

My advice to those of you who have a loved one who has been recently diagnosed with PD is to find long term care insurance, as my father requires nearly 24 hour aid.