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Q How does dementia associated with Parkinson's differ from dementia associated with Alzheimer's disease?
DR. JENNIFER G. GOLDMAN RESPONDS:
A Dementia is a general term that describes a decline in cognitive abilities that is severe enough to interfere with performing everyday activities and tasks. This decline can affect memory but also other cognitive abilities such as executive function (planning, organizing, multi-tasking, or solving problems), attention, language, and visual perception of spatial relationships. Dementia can occur in a number of neurologic conditions, including Alzheimer's disease (AD), stroke, Parkinson's disease (PD), dementia with Lewy bodies, and frontotemporal degeneration, among others. In each of these disorders, the person will experience symptoms of cognitive decline.
Dementia can occur with AD and PD. Both conditions are neurodegenerative, which means they involve gradual injury to cells in the brain. AD is the most common type of dementia, accounting for about 50–80 percent of dementias, especially in people over the age of 65 years. Patients with AD typically have difficulty remembering recent events, newly learned information, or names—particularly early in the course of the disease. Problems learning and retaining new information are common in early AD because the disease usually begins in the brain areas involved in memory and learning. AD can also cause confusion or disorientation, difficulty remembering directions from point A to point B, trouble communicating, difficulty with executive function, and poor judgment, especially as the disease progresses.
PD dementia, on the other hand, occurs later in the course of PD and in the setting of the motor symptoms associated with PD, such as resting tremor, slowness, stiffness, and gait or balance problems. Dementia in PD typically starts years after the onset of motor symptoms.
Certain dementia symptoms are more pronounced or unique to PD. The most common cognitive difficulties experienced in PD dementia are trouble with executive function, attention, and visual perception of spatial relationships. Problems with multi-tasking are common in PD dementia. Moreover, although “memory” complaints are often reported in PD, they may be due to underlying problems with attention, concentration, or executive function. PD patients with dementia perform better on memory tasks such as recognizing previously encountered events or items and when given clues or prompts to “retrieve” the event or item from their memory, even if they have trouble with tests of freely recalling items. This is in contrast to AD.
Both AD and PD are diseases associated with the accumulation of certain proteins in the brain and nervous system. However, the primary proteins involved—and disease processes—differ in the two conditions. In AD, a build-up of the proteins beta-amyloid and tau occurs, forming amyloid plaques and neurofibrillary tangles, respectively. In PD, an accumulation of the protein alpha-synuclein occurs, forming Lewy bodies.