Dementia prevalence in the general population
Most studies suggest that 5 to 8 percent of the over-65 population have some form of dementia and the number doubles every five years.
A study billed as the first of a nationally representative population in the U.S. found the prevalence of dementia among those age 71 and older was 13.9% and increased with age, from 5.0% of those aged 71-79 to 37.4% of those aged 90 and older.
A fairly recent study in Italy found the following prevalence of dementia in the specific age groups:
- 80-84 -- 14.6%
- 85-89 -- 32,8%
- 90-94 -- 40.6%
- 95+ -- 55.5%
Most studies have found the incidence of dementia to be higher among women than men, some finding the rate as much as 30% higher among women. But a caution is noted: Significantly fewer men reach these advanced ages.
And most studies find that almost three-quarters of all dementia is due to Alzheimer's.
Dementia prevalance among people with Parkinson's
The incidence of dementia is much higher among Parkinson's patients than in the general population. My neurologist, Dr. Laxman Bahroo at Georgetown University Hospital, said that 50% of Parkinson's patients experience some cognitive decline after 5 years with PD and 50% have dementia after 8 years.
The Parkinson Foundation's booklet on "Mind, Mood, & Memory" also says that 50% of people with PD end up experiencing some form of cognitive impairment. The booklet adds:
In the early stages of illness, many people with PD will complain of difficulties with attention and task completion . . . For example, the patient may complain of being easily distracted, losing their train of thought, or getting easily "knocked off track" when performing a task. In the middle stages of illness, difficulties with decision-making, problem-solving, memory and word-finding may become more apparent. In the latter stages of illness, a more serious cognitive disturbance can arise with confusion, visual hallucinations, delusions, and agitation. In general, mental and motor decline tend to occur in parallel as the disease progresses.One reason for the conflicting data on the prevalence of dementia is that some studies lumps people who have Dementia with Lewy Bodies (DLB) with those with Parkinson's dementia. Differentiating between the two is not clear cut. In Parkinson's, dementia usually develops years after the diagnosis of PD. In DLB, the dementia occurs at the same time, or shortly after, the development of Parkinson's.
Risk Factors for PD Dementia
The following factors make it more likely that someone with Parkinson's will develop dementia:
- Age 70 or older
- Score greater than 25 on the Parkinson's Disease rating scale (PDRS) that doctors use to check for PD progression
- Depression, agitation, disorientation, or psychotic behavior when treated with the PD med levodopa.
- Exposure to severe psychological stess
- Cardiovascular disease
- Low education level