What is Parkinson's disease dementia?

Parkinson's disease dementia is a decline in thinking and reasoning that develops in some people with Parkinson's at least a year after diagnosis. The Alzheimer's Association explains that Parkinson's brain changes begin in a region that controls movement and gradually spread, affecting memory, attention, judgment and planning. Common symptoms include visual hallucinations, paranoid ideas, muffled speech, depression and sleep problems.

It often does, but not always. The Parkinson's Foundation says recent research suggests up to 70 percent of people with Parkinson's will develop dementia as the disease progresses. It usually appears after many years of movement symptoms. Symptoms can include memory loss, confusion, mood changes, hallucinations, delusions and trouble with visual perception and language. Raise any change in thinking with the doctor.

The difference is timing. The Alzheimer's Association says the diagnosis is Parkinson's disease dementia when dementia begins at least one year, and usually several years, after Parkinson's movement symptoms. It is dementia with Lewy bodies when dementia comes before, at the same time as, or within a year of movement symptoms. Both involve Lewy bodies and are grouped as Lewy body dementia.

It varies widely. The Alzheimer's Association reports that some studies put the average time from the start of Parkinson's to dementia at about 10 years, and one large study found about three quarters of people living with Parkinson's for more than 10 years develop dementia. Once it begins, the speed of decline differs from person to person, so a doctor is the guide.

No treatment slows the brain cell damage, so care focuses on symptoms. The Alzheimer's Association says cholinesterase inhibitors may help with hallucinations, sleep and thinking, while carbidopa-levodopa for movement can sometimes worsen hallucinations and confusion. It advises avoiding antipsychotics such as haloperidol: about 60 percent of people with dementia with Lewy bodies who receive them have serious reactions. Work closely with the doctor on every medicine.