In plain English
Parkinson's Disease Dementia (ICD-11 6D85.0) develops in around 30 to 40 per cent of people with Parkinson's Disease at some point during the illness. By convention, dementia in this context is diagnosed when cognitive impairment develops more than a year after the onset of motor symptoms.
What Parkinson's Disease Dementia is
Parkinson's Disease Dementia (PDD) is a neurodegenerative dementia developing in the setting of established Parkinson's Disease. It shares the underlying alpha-synuclein pathology of Dementia with Lewy Bodies. The distinction between PDD and Dementia with Lewy Bodies is by convention timing: dementia developing more than a year after motor symptoms is PDD; dementia developing before or within a year of motor symptoms is Dementia with Lewy Bodies.
How common it is
Around 30 to 40 per cent of people with Parkinson's Disease develop dementia at some point. Risk rises with age, longer duration of Parkinson's Disease, and presence of Mild Cognitive Impairment earlier in the course.
How it presents
The cognitive profile differs from Alzheimer's Disease:
- Prominent attention and executive dysfunction;
- Reduced visuospatial skill;
- Fluctuating cognition over hours or days;
- Memory loss is often retrieval-type (better with prompts) rather than the dense storage failure of Alzheimer's;
- Visual hallucinations are common;
- REM Sleep Behaviour Disorder is often present.
How it is diagnosed
The diagnostic process emphasises history (with collateral), cognitive testing and clinical examination. Key elements:
- Established Parkinson's Disease (typically more than a year of motor symptoms);
- Significant cognitive impairment interfering with daily independence;
- Addenbrooke's Cognitive Examination with attention to attention, fluency, and visuospatial scores;
- Structural Magnetic Resonance Imaging to exclude other causes;
- Where uncertainty exists, DAT Scan showing reduced striatal dopamine transporter uptake supports the diagnosis.
Treatment
Several considerations are specific to PDD:
Cholinesterase Inhibitors
Rivastigmine is licensed for PDD and can produce meaningful improvement in attention, hallucinations and global function. Donepezil is also used. The benefit is often greater than in Alzheimer's Disease.
Memantine
May help in moderate to severe disease, though evidence is more limited than for Cholinesterase Inhibitors.
Parkinsonian medication
Levodopa typically remains the core treatment for motor symptoms. Dopamine agonists are generally avoided in PDD because they can worsen hallucinations. Anticholinergic Parkinson's medicines should be reviewed because of cognitive risk.
Antipsychotic medication
Used with extreme caution. Typical antipsychotics (Haloperidol) are contraindicated; severe sensitivity reactions can occur. Quetiapine at low dose, or Clozapine under specialist supervision, is preferred where antipsychotic medication is essential.
Autonomic and sleep features
PDD often involves autonomic dysfunction (postural drops in blood pressure, urinary symptoms, constipation, syncope) and sleep disturbance (REM Sleep Behaviour Disorder, daytime sleepiness, insomnia). Each needs specific management. See sleep disturbance and continence.
Falls and mobility
Falls are a major source of morbidity. Physiotherapy, occupational therapy, falls clinics and home assessment are valuable. See falls and mobility.
Where to be seen
PDD is typically co-managed between neurology (for Parkinson's motor management) and old age psychiatry or geriatric medicine (for dementia management). The Dementia Service can provide structured cognitive review where the cognitive picture is changing alongside established Parkinson's Disease.
Frequently asked questions
What is the difference between Parkinson's Disease Dementia and Dementia with Lewy Bodies?
By convention, timing: cognitive symptoms more than a year after motor symptoms is PDD; within a year is Dementia with Lewy Bodies. The underlying pathology and treatment overlap substantially.
Will everyone with Parkinson's Disease develop dementia?
No. Around 30 to 40 per cent develop dementia at some point. Risk increases with age and longer Parkinson's duration.
Are Cholinesterase Inhibitors effective in PDD?
Yes. Rivastigmine is licensed for PDD and often produces meaningful benefit, particularly for attention and hallucinations.
Should I stop my Parkinson's medication?
Not without specialist advice. Levodopa is usually continued. Dopamine agonists and anticholinergic Parkinson's medicines may need review because of cognitive effects.
Can antipsychotic medication be used for hallucinations?
Only with extreme caution. Typical antipsychotics (Haloperidol) are contraindicated. Quetiapine at low dose, or Clozapine under specialist supervision, is preferred where antipsychotic medication is essential.
References
- World Health Organization. ICD-11 6D85.0 Dementia due to Parkinson's Disease.
- Aarsland D et al. Parkinson's Disease-associated cognitive impairment. Nat Rev Dis Primers 2021.
- NICE NG71: Parkinson's Disease in adults.
- Parkinson's UK. Dementia and Parkinson's.