If you have Parkinson’s disease, you may have heard that dementia is something to watch for. Around one in three people with Parkinson’s will develop it. But here is something that often gets overlooked: there are several different types of dementia that can affect people with Parkinson’s — and they are not all the same.

The type matters. It affects what symptoms to expect, which medications are safe, and what the future might look like. This post explains the main types in plain language.

Parkinson’s Disease Dementia

This is the most common type for people living with Parkinson’s. It develops after someone has already had Parkinson’s for a while — usually many years after motor symptoms like tremor or stiffness began.

As Parkinson’s progresses, the same protein clumps that cause motor problems — called Lewy bodies — spread further into the brain. When they reach areas involved in thinking, cognitive problems begin.

The main symptoms are:

• Thinking and processing more slowly than before
• Difficulty concentrating or multitasking
• Problems with visual tasks, like judging distances or reading a map
• Seeing things that aren’t there (visual hallucinations) — often people or animals

Memory is affected, but it tends to be less severely than in Alzheimer’s disease. The motor symptoms of Parkinson’s — tremor, stiffness, slowness — are still present and usually noticeable.

Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) is caused by the same type of protein clumps as Parkinson’s disease dementia. The difference is the timing. In DLB, thinking and psychiatric symptoms come first. Motor symptoms, if they appear at all, tend to be mild at the start.

The three main features are:

Fluctuating alertness. Attention and awareness can change a lot from day to day, or even hour to hour. Someone may seem perfectly clear one moment and confused the next.

Visual hallucinations. These are vivid and often very detailed — seeing people, children, or animals that are not there. They tend to occur regularly.

REM sleep behaviour disorder. This means acting out dreams during sleep — talking, shouting, or moving around. It can happen years before any other symptoms appear.

One very important point about DLB: people with this condition can have a serious — sometimes life-threatening — reaction to certain antipsychotic medications. These drugs are sometimes prescribed for hallucinations. If hallucinations are a symptom, it is essential that doctors consider DLB before prescribing anything. Always mention this to any doctor or hospital involved in your care.

Alzheimer’s Disease

Alzheimer’s is the most common dementia overall. It can also affect people with Parkinson’s disease.

The main early symptom is memory loss — specifically, difficulty forming new memories. This is different from the memory difficulties in Parkinson’s disease dementia, where the problem is more about retrieving information than storing it.

Typical early signs include:

• Asking the same questions repeatedly
• Forgetting recent conversations or events
• Getting lost in familiar places

Physical Parkinson’s symptoms are not a feature of early Alzheimer’s. They can appear in later stages but are not what drives the diagnosis.

Vascular Dementia

Vascular dementia is caused by reduced blood flow to the brain — either from strokes or from gradual narrowing of small blood vessels over time.

It tends to affect thinking speed and planning first. Memory may be less affected early on. Decline can happen in steps — noticeably worse after a stroke — or it can be more gradual.

A slow, shuffling walk is common because of damage to movement-related brain circuits. However, the classic Parkinson’s tremor is not usually a feature, which helps tell the two conditions apart.

Risk factors include high blood pressure, diabetes, and atrial fibrillation. Managing these well is one of the most important things anyone can do to reduce the risk of vascular dementia.

Genetic Frontotemporal Dementia with Parkinsonism (FTDP-17)

This is a rare inherited condition caused by a mutation in the MAPT gene, which controls a brain protein called tau. It runs in families and follows a clear pattern across generations.

In FTDP-17, personality and behaviour change first. Memory tends to be relatively preserved early on. The changes are often striking — a fundamental shift in how someone acts, how they treat others, or what they find appropriate.

Parkinsonism — stiffness, slow movement — develops as part of the same condition. It usually does not respond well to levodopa.

If dementia and Parkinsonism both appear in multiple family members across generations, it is worth asking a doctor about genetic testing.

Atypical Parkinsonism — PSP, CBD and MSA

These three conditions are sometimes called “Parkinson’s plus” syndromes. They cause Parkinsonism — similar motor symptoms to Parkinson’s — but they are distinct diseases with their own features.

Progressive supranuclear palsy (PSP) causes early falls, often backwards. Eye movement becomes difficult, particularly looking up or down. Balance and speech are affected. Levodopa — the standard Parkinson’s medication — gives little or no benefit.

Corticobasal degeneration (CBD) tends to affect one side of the body much more than the other. One arm or hand may become increasingly stiff and clumsy. Some people experience alien limb syndrome — the hand moves on its own and does not feel like it belongs to them. Again, levodopa typically does not help much.

Multiple system atrophy (MSA) combines Parkinsonism with problems in the autonomic nervous system — the system that controls blood pressure, bladder function, and digestion. Dizziness when standing up and bladder difficulties are common early symptoms. Balance and coordination can also be affected.

In all three conditions, a poor response to levodopa is an important clue that something other than typical Parkinson’s disease may be the diagnosis.

How to Tell Them Apart — Three Simple Questions

If you are trying to make sense of a diagnosis, these three questions are a useful starting point:

What came first? Motor symptoms before thinking problems suggest Parkinson’s disease dementia. Thinking or behaviour problems first suggest DLB or frontotemporal dementia. Memory loss first suggests Alzheimer’s.

What kind of cognitive problems? Difficulty with memory and forming new memories points toward Alzheimer’s. Difficulty with concentration, speed, and multitasking is more typical of Parkinson’s disease dementia, DLB, or vascular dementia. Personality and behaviour change, with memory relatively intact, points toward frontotemporal dementia.

How does the Parkinsonism behave? Classic Parkinson’s symptoms that respond well to levodopa suggest Parkinson’s disease dementia. Parkinsonism that does not respond to levodopa — or that comes with unusual features like early falls or one-sided symptoms — suggests one of the atypical conditions.

Why Does This Matter?

Getting the right diagnosis makes a real difference.

Some medications that are safe in Alzheimer’s or Parkinson’s disease dementia can be harmful — even dangerous — in DLB. Knowing which condition is present helps doctors choose treatments carefully.

Understanding the type of dementia also helps families know what to expect and what support is available. Different conditions have different timelines and different needs.

If you are worried about cognitive symptoms — in yourself or someone you care for — the most important step is to raise it with your neurologist or specialist nurse. Cognitive changes in Parkinson’s are common, they can be assessed properly, and there is support available.

Disclaimer & References

This post is for general information only. It is not a substitute for advice from your own medical team. Our team uses AI to assist in writing posts but the final check is always done by a human.

You can find more information on 

National Institute of Aging – What is dementia –

https://www.nia.nih.gov/health/alzheimers-and-dementia/what-dementia-symptoms-types-and-diagnosis

Dementia UK. Types of dementia https://www.dementiauk.org/information-and-support/types-of-dementia/parkinsons/

Alzheimer’s association – Different types of dementia – https://www.alz.org/getmedia/56ced842-e341-44fd-ad1b-7a5d8d23bf9d/differentialdiagnosishandout.pdf

National Institute of Aging – What is dementia –

https://www.nia.nih.gov/health/alzheimers-and-dementia/what-dementia-symptoms-types-and-diagnosis

Dementia UK. Types of dementia https://www.dementiauk.org/information-and-support/types-of-dementia/parkinsons/

Alzheimer’s association – Different types of dementia – https://www.alz.org/getmedia/56ced842-e341-44fd-ad1b-7a5d8d23bf9d/differentialdiagnosishandout.pdf