November 18, 2015

Parkinson's Disease and Dementia: An Overview

My effort to recap the connection between Parkinson’s disease (PD) and dementia -- including Alzheimer’s disease (AD) -- encountered one main complication: different writers define important key terms in different, sometimes inaccurate, ways. I’ve done my best here to untangle those complications.  

Mild Cognitive Impairment (MCI) 
Mild cognitive deficits that do not impair one's ability to carry out routine daily activities have been labeled "mild cognitive impairment." Estimates on the prevalence of cognitive changes in people with Parkinson's disease (PD) vary greatly, mainly because reviewers have used different means to identify and define impairments. They’ve also selected study participants at different stages of the disease.

Estimates suggests that one quarter to one third of all people with PD will suffer some mild cognitive impairment. Attention, working memory, executive function, and visuospatial function are the most frequently affected cognitive domains for those of us with the disease.

Doctors used to believe that cognitive changes did not develop until mid- to late-stage Parkinson's, but recent research suggests that mild changes may be present as early as the time of diagnosis.

recent study reported that nearly half of all PD patients develop cognitive impairment within about a decade, and progress rapidly to dementia.

Dementia isn’t a specific disease; instead, it’s a general term for a decline in mental ability severe enough to interfere with daily life. It indicates problems with brain functions like memory, judgment or language. It can also make some regular daily activities – like paying bills or driving – impossible.

Although memory loss generally occurs in dementia, memory loss alone doesn't mean you have dementia. To a certain extent, memory loss is a normal part of aging.

Symptoms of dementia have many causes. Alzheimer's disease is the most common cause of progressive dementia, accounting for 60-80% of cases. Vascular dementia, which occurs after a stroke, is the second most common dementia type.

But there are many other conditions that can cause symptoms of dementia, including some that are reversible, such as thyroid problems and vitamin deficiencies.

Dementia is often incorrectly referred to as "senility," which reflects an early, incorrect belief that serious mental decline is a normal part of aging.

At least two of the following core mental functions must be significantly impaired to be considered dementia:
  • Memory
  • Communication and language
  • Ability to focus and pay attention
  • Reasoning and judgment
  • Visual perception

Alzheimer's Disease  
AD is a progressive, degenerative disorder that attacks the brain's nerve cells (neurons), resulting in behavioral changes, loss of memory, and compromised thinking and language skills.

Two types of abnormal lesions clog the brains of individuals with AD:
  • Beta-amyloid plaques -- sticky clumps of protein fragments and cellular material that form outside and around neurons,
  • Neurofibrillary tangles -- insoluble twisted fibers composed largely of the protein tau that build up inside nerve cells.
Although these structures are hallmarks of the disease, scientists are unclear whether they are a cause or a byproduct.

Parkinson's Disease and Dementia
The changes caused by PD begin in a brain region that plays a key role in movement. As those brain changes gradually spread, they often begin to affect mental functions like memory, and the ability to pay attention, make sound judgments and plan the steps needed to complete tasks.

The key brain changes linked to PD and Parkinson's disease dementia are abnormal microscopic deposits composed chiefly of alpha-synuclein, a protein found in the brain whose function isn't yet clearly understood. These deposits are called "Lewy bodies."

Lewy bodies are also found in several other brain disorders, including dementia with Lewy bodies (DLB). Evidence suggests that DLB, PD, and Parkinson's disease dementia may be linked to the same underlying brain abnormalities caused by alpha-synuclein.

There's another complication: many people with DLB and Parkinson’s dementia also have plaques and tangles, the hallmark brain changes linked to Alzheimer's disease.

Estimates suggest that 50-80% of people with PD eventually experience dementia as their disease progresses. The average time from PD onset to development of dementia is about 10 years.

Tomorrow, we’ll take a closer look at Parkinson's disease dementia and dementia with Lewy bodies.

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