Parkinson's Disease Dementia

Parkinson's disease dementia (PDD) refers to a decline in thinking, reasoning and behaviour that eventually affects many people with Parkinson's disease.

Parkinson's disease is a fairly common neurological disorder, estimated to affect nearly two per cent of people older than age 65.

The prevalence of dementia in people with Parkinson’s disease at a given point of time (referred to as Point Prevalence) is estimated at around 25-35 per cent. Dementia frequency increases with disease duration and with age. Most individuals with Parkinson’s disease have cognitive impairment by 15 years of disease duration, either in the form of Parkinson’s disease dementia (PDD) 48 per cent or mild cognitive impairment (MCI) 36 per cent. In people with Parkinson’s disease surviving to 20 years with the disease, the prevalence of dementia increases to over 80 per cent, with most individuals showing evidence of dementia before death.

The brain changes linked to Parkinson's disease and PDD are abnormal microscopic deposits of alpha-synuclein protein, called Lewy bodies. Lewy bodies are also found in several other brain disorders, including dementia with Lewy bodies. Evidence suggests that dementia with Lewy bodies (LBD), Parkinson's disease and PDD may be linked to the same underlying abnormalities in brain processing of alpha-synuclein. 

Many experts now believe that PDD and LBD are two different expressions of the same underlying disease Lewy body dementia, associated with problems with brain’s processing of alpha-synuclein protein. 

Another confounding factor is that many people with both dementia with Lewy bodies and PDD also have the hallmark features of Alzheimer's disease – plaques and tangles.

What are the symptoms of Parkinson’s disease dementia? 

PDD is associated with cognitive and behavioural changes including features of psychosis. The fluctuating cognitive features include impaired attention, concentration and judgement, memory changes and difficulty learning new information, problems with visual perception, word-finding difficulties and difficulty understanding complex sentences.

Behavioural changes include apathy, depression, anxiety and visual hallucinations (complex and specific, involving people, animals or objects), having delusions (false, fixed belief that is maintained despite evidence to the contrary) and excessive daytime sleepiness.

How is Parkinson’s disease dementia diagnosed?

There is no single test or any combination of tests, that conclusively determines that a person has PDD. 

If people have established Parkinson’s disease and develop dementia in a pattern consistent with PDD, additional testing may not be required:

Since people with Parkinson's are at high risk for dementia as their disease progresses, doctors monitor those with Parkinson's closely for signs of cognitive changes. When someone with Parkinson's develops cognitive changes, doctors often order magnetic resonance imaging (MRI) of the brain to rule out tumours, structural changes and evidence for vascular disease.

If atypical features are seen in the history, examination or neuropsychological testing, the workup may include evaluations for overlapping processes, such as an MRI to look for features of Alzheimer’s disease, besides looking for vascular changes. Studies have shown that most people with Lewy body dementia are quite likely to have Alzheimer’s changes in the brain as well. This should not lead to exclusion of PDD diagnosis but should list Alzheimer’s changes as a comorbid process.

What are the factors that increase the risk of progression of Parkinson’s disease to Parkinson’s disease dementia?

Certain factors at the time of Parkinson's diagnosis may indicate a higher future dementia risk, including older age, greater severity of motor symptoms and having mild cognitive impairment.

  • Additional risk factors may include: 
    • Hallucinations in a person who doesn't yet have other dementia symptoms
    • Excessive daytime sleepiness and postural instability and gait disturbance (PIGD) including "freezing" in mid-step
    • Difficulty initiating movement,
    • Shuffling, problems with balance and falling


There are currently no treatments to slow or stop the brain cell damage caused by PDD. Current strategies focus on alleviating symptoms.

Treatment considerations involving medications include the following: 

  • Cholinesterase Inhibitors, the mainstay for treating Alzheimer's, may also help PDD symptoms.  Antipsychotic drugs should be used with extreme caution in PDD, since they may cause serious side effects in as many as 50 per cent of those with PDD and LBD. Side effects may include sudden changes in consciousness, impaired swallowing, acute confusion, episodes of delusions or hallucinations, or appearance or worsening of Parkinson's symptoms. 
  • L-dopa may be prescribed to treat Parkinson's movement symptoms but it could aggravate hallucinations and confusion in those with PDD and Lewy body dementia. 
  • Antidepressants may be used to treat depression, which is common in both PDD and Lewy body dementia. 
  • Clonazepam may be prescribed to treat sleep behaviour disorder if any.

Like other types of dementia, PDD may get worse over time and speed of progression can vary from person to person.

Nonpharmacologic approaches are an important aspect of treating individuals with Parkinson’s disease. Exercise and physical activity have been shown to very beneficial for people with PDD, often resulting in enduring benefits. Physical therapy, occupational therapy, and speech-language pathology assessments (addressing both speech and swallowing) are also important considerations of care. Therapy sessions should include both patients and caregivers to compensate for cognitive limitations of patients and to teach caregiver-specific skills. Swallow assessments are critical given that respiratory causes of death are common in people with Parkinson’s disease dementia.



Further Information