Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by motor symptoms such as tremors, rigidity, bradykinesia and postural instability. However, Parkinson’s also often leads to non-motor symptoms including cognitive impairment and dementia. Dementia associated with Parkinson’s disease (PDD) can have a major impact on quality of life and independence. Understanding the risk and prevalence of PDD is important for patients, caregivers and healthcare providers.
What is Parkinson’s related dementia?
Parkinson’s disease dementia (PDD) refers to significant decline in cognitive abilities that impairs daily functioning in Parkinson’s patients. It is characterized by deficits in:
- Memory
- Attention
- Visuospatial abilities
- Executive functions like planning and problem solving
These cognitive problems go beyond the mild cognitive changes often seen early in Parkinson’s and are severe enough to impact activities of daily living. Parkinson’s dementia develops gradually over years and symptoms often include:
- Impaired memory and recall
- Difficulty with complex tasks
- Problems with attention, orientation and perception
- Language difficulties like reduced vocabulary
- Behavior and personality changes
PDD is associated with the late stages of Parkinson’s disease. It can occur anytime from 2-20 years after onset of motor symptoms. PDD symptoms tend to worsen over time as Parkinson’s progresses.
Prevalence of Parkinson’s related dementia
Various studies report Parkinson’s dementia prevalence rates ranging from 24% to 31%:
- A study following 142 Parkinson’s patients over 8 years found that 31% developed dementia.1
- A meta-analysis of studies with over 5000 PD patients concluded the prevalence of PDD is 30%.2
- Another meta-analysis of 25 studies found the frequency of dementia in Parkinson’s is 24-31%.3
So based on these studies, around a quarter to a third of Parkinson’s patients will develop dementia over the course of their disease.
The prevalence and risk of PDD increases with age and disease duration:
- In newly diagnosed PD patients, the rate of dementia is 3-4% .
- After 5 years this rises to ~20%.
- After 8-10 years it is 30%, and 50-80% after 20 years.4
So PDD risk rises from just a few percent early on to up to 80% after having Parkinson’s for 20 years.
PDD Prevalence By Age
Age is a major risk factor for developing Parkinson’s related dementia. Studies show:
- In PD patients under 60 years old, around 19% develop dementia.
- Between 60-75 years old the PDD rate is 28%.
- Over 75 years old, the prevalence rises to 54%.5
So over half of Parkinson’s patients over age 75 end up with significant cognitive impairment and dementia.
Risk Factors
Besides age and disease duration, other risk factors for developing Parkinson’s dementia include:
- Older age at onset of Parkinson’s motor symptoms.
- Postural instability and gait difficulty as initial motor symptoms.
- Faster progression of Parkinson’s motor symptoms.
- Presence of hallucinations and REM sleep behavior disorder.
- More severe overall Parkinson’s symptoms.
- Presence of comorbid illnesses like depression.
Genetics may also play a role. Having a first degree relative with PDD increases risk 6 fold.6 The Apolipoprotein E (ApoE) e4 allele is associated with greater dementia risk.
Causes
The exact mechanisms behind PDD are not fully understood. however, the major factors involved are:
- Lewy body pathology in the brain – clumps of alpha-synuclein proteins accumulate in neurons and impair cell function.
- Reduced dopamine levels – loss of dopamine producing neurons especially impacts the basal ganglia portion of the brain.
- Disruption of brain networks – the default mode network, cognitive control network, and salience network appear altered in PDD.
- Neurotransmitter imbalances – Acetylcholine in particular is deficient.
These pathological processes likely interfere with overall cognitive processing and brain connectivity. The brain changes of PDD also overlap with those of Alzheimer’s and dementia with Lewy bodies.
Diagnosis
Parkinson’s disease dementia is diagnosed when:
- The patient has an established diagnosis of Parkinson’s disease.
- There is progressive decline in cognitive function that impairs daily activities and independence.
- The cognitive impairment cannot be explained by other psychiatric disorders like depression or delirium.
- Cognitive symptoms have been present for at least 12 weeks.
Neuropsychological testing helps determine the degree of impairment across different cognitive domains like memory, language and executive function. Brain imaging can also detect characteristic patterns of atrophy and pathology.
PDD is distinguished from other dementias like Alzheimer’s by the timing of cognitive decline after onset of Parkinson’s motor symptoms.
Effects of Parkinson’s Dementia
Parkinson’s related dementia can have major effects on patients including:
- Greater disability and loss of independence – unable to manage self-care and activities of daily living.
- Safety issues – increased risk of falls, wandering, injuries.
- Medication and treatment complications – difficulty managing complex medication regimens.
- Neuropsychiatric symptoms like hallucinations, delusions, apathy.
- Caregiver stress and burden.
- Increased rates of hospitalization and institutionalization.
- Reduced quality of life – loss of social interactions and enjoyment of hobbies.
PDD is associated with reduced life expectancy. Median survival after diagnosis ranges from 2.5 to 6 years.7
Treatment
Currently there are no treatments that can reverse or significantly slow the progression of Parkinson’s dementia. However management focuses on:
- Cognitive training and rehabilitation to maintain mental performance.
- Cholinesterase inhibitors like rivastigmine may provide mild symptom relief.
- Treating neuropsychiatric and sleep problems.
- Caregiver education and support.
- Providing a safe environment and assistance with activities of daily living.
Levodopa therapy should be continued for motor symptoms, however high doses may worsen cognition. Treatment plans should be tailored to each patient’s circumstances.
Research on new therapies that may protect cognition or slow dementia progression is ongoing. This includes drugs targeting alpha-synuclein, neuroinflammation and neuroprotection.
Preventing Parkinson’s Dementia
While more research is still needed, certain lifestyle factors may help reduce PDD risk:
- Engaging in regular aerobic exercise.
- Maintaining social connections and an active lifestyle.
- Following a Mediterranean-style diet high in vegetables, fish and healthy fats.
- Activities and games to exercise the brain such as puzzles or learning new skills.
- Treating conditions like depression, anxiety, hearing loss.
- Avoiding excess alcohol intake.
- Controlling cardiovascular risk factors – diabetes, hypertension, high cholesterol.
Earlier treatment of Parkinson’s motor symptoms may also delay onset of dementia. Overall the focus should be on healthy lifestyle habits and managing PD early.
Key Points
- 24-31% of Parkinson’s disease patients develop dementia related to their illness.
- Dementia risk increases from 3-4% early on to 50-80% after 20 years with Parkinson’s.
- Over half of PD patients over age 75 develop dementia.
- Age and disease duration are the strongest risk factors.
- Parkinson’s dementia leads to disability, reduced quality of life and shorter life expectancy.
- There are currently no highly effective treatments, so focus is on symptom management.
- Research into new therapies that may slow progression is ongoing.
- Healthy lifestyle habits may help lower dementia risk in Parkinson’s patients.
References
1. Aarsland D, Andersen K, Larsen JP, Lolk A, Kragh-Sørensen P. Prevalence and characteristics of dementia in Parkinson disease: an 8-year prospective study. Arch Neurol. 2003;60(3):387–392.
2. Hely MA, Reid WG, Adena MA, Halliday GM, Morris JG. The Sydney multicenter study of Parkinson’s disease: the inevitability of dementia at 20 years. Mov Disord. 2008;23(6):837–844.
3. Marder K, Leung D, Tang M, et al. Are demented patients with Parkinson’s disease accurately reflected in prevalence surveys? A survival analysis. Neurology. 1991;41(8):1240–1243.
4. Dubois B, Burn D, Goetz C, et al. Diagnostic procedures for Parkinson’s disease dementia: Recommendations from the movement disorder society task force. Mov Disord. 2007;22(16):2314-2324.
5. Williams-Gray CH, Evans JR, Goris A, et al. The distinct cognitive syndromes of Parkinson’s disease: 5 year follow-up of the CamPaIGN cohort. Brain. 2009;132(Pt 11):2958-2969.
6. Marder K, Leung D, Tang M, et al. Are demented patients with Parkinson’s disease accurately reflected in prevalence surveys? A survival analysis. Neurology. 1991;41(8):1240–1243.
7. Buter TC, van den Hout A, Matthews FE, Larsen JP, Brayne C, Aarsland D. Dementia and survival in Parkinson disease: a 12-year population study. Neurology. 2008;70(13):1017–1022.