Skip Navigation

Parkinson's disease dementia

Dementia is a disorder characterised by memory and thinking problems that may occur in a group of diseases: Alzheimer's disease, frontotemporal dementia, vascular dementia, Dementia with Lewy Bodies (DLB), and also Parkinson's disease dementia.

In Parkinson's, dementia may manifest at least a year after initial motor symptoms, or later. Most people with Parkinson’s who have dementia develop it as a result of their Parkinson’s though, rather than because of other underlying cognitive causes.

Image by ©JonnyAcheson2019

What is dementia?

Dementia is characterised by deterioration in cognitive abilities – it can affect concentration, memory and thinking which can in turn impact on many aspects of daily life and quality of life. Initially, difficulties can be quite mild and so the term ‘mild cognitive impairment' (MCI) is used.

There are different forms of dementia caused by variety of diseases, affecting each person in an individual way. As initial symptoms appear gradually, a person with dementia may be unaware of their difficulties. Friends, family, and colleagues are likely to notice first and often to take the initial steps towards managing problems.

Dementia with Lewy bodies (DLB) is a similar condition to Parkinson's. This is diagnosed when someone has the symptoms of dementia either before or at the same time as developing Parkinson’s-like problems with movement (motor symptoms). In some cases, no motor symptoms may develop at all.

The most common form of dementia is Alzheimer’s disease, accounting for approximately two thirds of all dementia cases.

Parkinson's disease dementia

Many people with Parkinson’s complain of changes in their thinking and mental abilities but comparatively few go on to develop dementia. However, it is thought that most people with Parkinson’s experience some degree of mild cognitive impairment (MCI).

MCI is a disorder that may occur at any time in the course of Parkinson’s. Key features that may be experienced are problems with sustained attention, working memory, verbal memory and fluency. MCI occurs more frequently in older people and when motor symptoms are more advanced.

Dementia symptoms vary widely from one person to another and may fluctuate in severity throughout the day. Common symptoms include:

  • reduced concentration, forgetfulness and slow thought processes. This can make it hard to follow a conversation and communicate
  • reduced short term memory span, making it hard to recall names or when events occurred. Long term memory may still be good though, so events from the past may be clearly recalled
  • difficulties with decision making, planning activities and problem solving. This can make everyday activities such as dressing or preparing meals increasingly difficult
  • difficulties doing more than one thing at a time, for example walking and talking
  • reduced energy levels, reduced appetite and altered sleeping patterns. Daytime napping may increase as a result
  • a lack of interest in things that were previously enjoyed and a general lack of motivation
  • changes in personality, for example anxiety, irritability, obsessive tendencies, or difficulty controlling emotions
  • visual hallucinations and delusions in some people.

In Parkinson’s disease dementia, impairment of memory is less severe than in Alzheimer’s, and the ability to carry out daily activities is usually retained. More characteristic signs are poor perception, reduced vocabulary and difficulties with complex sentences, behavioural disorders with personality and mood changes, sometimes hallucinations and delusions, or apathy, anxiety, and excessive daytime sleepiness.

What causes Parkinson’s dementia?

The mechanisms of dementia are not yet fully understood, although we know that the process involves neurodegeneration (loss of cerebral neurons). It is not possible to predict who will be affected. The most notable risk factors are:

  • advancing age – there is a much lower incidence of dementia in people under 50 years of age. Usually a number of years pass from being diagnosed with Parkinson’s to the onset of dementia, maybe up to 15 years in some cases
  • poor motor response to levodopa treatment
  • falls
  • changes in the structure and chemistry of the brain - the process that causes of the loss of dopamine cells in the brain is thought to be responsible for cognitive changes
  • microscopic deposits, or Lewy bodies, in the nerve cells of the brain stem
  • hallucinations or delusions early on in the condition increases the risk of developing dementia
  • non-motor symptoms: hyposmia (loss of sense of smell), dysautonomias (disorders of the autonomic nervous system which regulates involuntary or unconscious processes in the body), REM-sleep disorder
  • a higher risk of dementia in people who were diagnosed with Parkinson’s late in life and have had the condition for a long time, or who have relatives with dementia.


Diagnosis is generally based on clinical symptoms, medical history and examination. Dementia is diagnosed by neuropsychological tests involving concentration, memory, language and problem-solving skills, but also imaging can help assess the extent of structural and molecular changes in the brain; laboratory testing of cerebrospinal fluid or genetic factors may give additional clues. Information from family members or carers may also be helpful in understanding how difficulties affect daily life.

Recognised 'rating scales’ are often used, with responses to carefully chosen questions rated to quantify cognitive problems. Rating scales are also useful in monitoring any improvement or decline during and after treatment.

For more subtle or complex difficulties a neuropsychologist  a psychologist with expertise in how behaviour and cognitive abilities are affected by brain diseases – may also make a more detailed assessment. This can be particularly helpful in differentiating Parkinson’s dementia from other conditions such as Alzheimer’s, stroke or dementia with Lewy bodies.

A neurologist will also rule out other medical conditions which may cause dementia-like symptoms, such as infection, medication side effects or depression.

Other factors, such as the onset of dementia in the early stages of living with Parkinson’s or unusual symptoms, could suggest that Parkinson’s is not the sole cause of dementia. In such cases, brain scans and blood tests may be recommended to search for other treatable causes, for example thyroid disease or vitamin B12 deficiency.


Treatment for dementia is complex and should be managed by the various members of the healthcare team who are experienced in treating both Parkinson’s and dementia. Non-medication management of Parkinson’s disease dementia includes cognitive training, exercise and physical interventions, adapting the person’s environment to ensure it does not aggravate problems, and appropriate information for patients and their carers.


Current medications will first be reviewed as some may have side effects that can worsen cognitive function. However, treating dementia often requires a careful balance between managing Parkinson’s symptoms and problems caused by dementia.

Depending on the severity of dementia and overall general health, dementia medications may be prescribed, including cholinesterase inhibitors or NMDA antagonists. These cannot cure dementia but help to preserve cognitive functions as long as possible. For behavioural problems, such as agitation, confusion, hallucinations or delusions, neuroleptic medications may be considered but these should be monitored carefully as they are not suitable for everyone. Medications improving attention and reducing daytime sleepiness may be helpful in some cases, which can improve quality of life.

Often several medications will be needed, to treat motor difficulties, cognitive problems, psychiatric symptoms, and autonomic dysfunction, always giving consideration to the risk-benefit ratio before starting new medications. Usually, one drug is started at a time, at a low dose, and then increased as needed.

Dementia can affect the ability to drive, so regular assessments should be carried out to establish if it is still safe to drive.

Advice for carers, family and friends

Living with or caring for someone with Parkinson’s disease dementia can be challenging. Sometimes help and support will be relied on heavily but there will be times when it will be better to step back and allow the person with dementia to do things for themselves. This balance will be difficult to judge at first, but with time and patience new routines and approaches to day-to-day living can be established.

It is important to encourage, stimulate and help the person with dementia, but remember too that rest is important.

Practical advice

Keep to a daily routine as much as possible. This will help with remembering when regular things, such as mealtimes, happen.

Adapting the home environment can play an important role, for example removing clutter can reduce the number of visual distractions as well as make it easier to move around. It generally helps to keep furniture in the same place and at night it may be useful to keep a low-level night light on to minimise any possible disorientation if the person you care for wakes.

As time passes and memory worsens, try using memory aids around the home such as large-print calendars and newspapers, clocks, alarms and easy to follow lists displayed on a pin-board or white-board. Labels on cupboards and boxes can also help.


A combination of both cognitive difficulties and some Parkinson’s symptoms can make speech and conversation difficult. Over time, the ability to remember words may be affected, vocabulary can become limited and humour less understood. Automatic responses, such as ‘hello’ or ‘goodbye’ tend to be retained for longer, while responses that require more careful thought processing are lost sooner.

Responses may be given out of sequence, or appear self-centred as it becomes more difficult for the person to relate to others in a conversation. Someone with dementia will find it harder to follow a conversation and sometimes things they say may not make sense and become confused, or perhaps they will repeat a few limited phrases over and over as they forget what they have already said.

The following communication tips may help if you are communicating with someone who has dementia:

  • Make sure you have the person’s attention before you communicate.
  • Minimise distractions such as the television or radio, or crowded places.
  • Be calm, speak very clearly and be patient, giving the person plenty of time to understand and respond.
  • Keep information simple, repeating if necessary, or break things down into manageable chunks and make one point at a time.
  • Use names rather than ‘he’ or ‘she’ as this will remind the person who you are talking about.
  • Try not to ask questions that require complicated answers.
  • Make eye contact and use gestures, facial expressions or touch as these can provide additional cues. Look out for their body language too as this can help you interpret what they want to communicate.
  • Remember that too many people taking part in a conversation can make it confusing for them to follow.
  • Try to communicate important information when medication is working well and the person with dementia is ‘on’.
  • Listen well, and don’t interrupt or finish sentences for the person.
  • Show respect and remember that the person still has the same feelings as they did before they developed dementia; don’t be patronising and do include them in social groups still.
  • Avoid talking about the person as if they were not there.
  • If the person confuses fact with fantasy, try to find ways around the situation rather than contradicting them completely.
  • Remember that humour helps relieve tension. Sometimes laughing about misunderstandings helps!

For further tips to help with communicating with people with Parkinson’s, see Caring and Parkinson’s.

Getting support

As dementia advances, support and respite will be essential for the spouse or carer. There are many trained professionals who can provide expert help and advice, as well as organisations such as carer support groups. Your doctor, neurologist or social workers can help with suggestions, or you may find contacts online.

For further information on carers and helpful organisations see Caring and Parkinson’s.

Content last reviewed: June 2020


We would like to thank Professor Pille Taba (University of Tartu, Estonia) for her help in reviewing this information.

Our thanks to Parkinson's UK for permission to use the following source(s) in compiling this information:

Related reading

Articles from Parkinson's Life online magazine

Back to top