Dementia is not a disease in itself. It is a word used to describe a group of symptoms that occur when brain cells stop working properly. This happens inside specific areas of the brain and can affect how you think, remember, and communicate. The symptoms of dementia are caused by diseases that affect the brain, Alzheimer’s disease being the most common. Other common forms of dementia include vascular dementia, dementia with Lewy bodies and frontotemporal dementia.

A rare disease is defined by the UK Government as one that affects less than five in 10,000 people in the general population, or one in every 2,000 people.

If you’re worried about any of these conditions, a doctor can test for these conditions separately to ensure that a correct diagnosis is given.

This section of our website provides information about these rare conditions. The conditions have been divided into two categories: those that directly cause dementia, and those that can cause memory and cognitive problems similar to symptoms seen in dementia. We also provide information about organisations that offer specific help and support for people affected by these conditions.

Rare forms of dementia

Other conditions that can cause dementia symptoms

Chronic traumatic encephalopathy (CTE)

Chronic traumatic encephalopathy is a brain condition associated with repeated blows to the head. Early symptoms of CTE usually appear around 10 years after brain injuries occur, but changes can be gradual and not always noticeable at first.

Research suggests that people with a traumatic brain injury could be 1.5 times more likely to develop dementia. But head injuries can vary enormously, and so can the diseases that cause dementia, so the relationship is hard to unravel.

We do know, however, that CTE is one type of dementia specifically linked to head injury. In CTE, a protein called tau forms clumps that spread throughout the brain, damaging brain cells. Possible signs of CTE are problems with thinking and memory, personality changes, and behavioural changes including aggression and depression.

A definite diagnosis of CTE can only be made after someone dies. This is because the damage caused by CTE can only be confirmed by looking closely at the brain through a post-mortem. However, a doctor can make a probable diagnosis based on a conversation about any symptoms, and the results of some simple mental and physical tasks.


The Concussion Foundation provides some helpful information about CTE on their website.

The NHS provides more information about the condition that you may find useful.

older man outside

Corticobasal syndrome (CBS)

Corticobasal syndrome usually affects people aged between 50 and 70. The condition is estimated to affect five people in every 100,000 in the general population. You may also hear it called corticobasal degeneration (CBD).

CBS is a condition that can cause people to have problems with movement. This can include muscle stiffness, numbness, and jerky movements. One side of the body is often affected first, such as difficulty controlling an arm. This is sometimes known as ‘alien limb’. This can spread to other parts of the body over time.

Other symptoms include slow and slurred speech, difficulty swallowing, impulsive behaviour, and problems with balance.

People with CBS may struggle with planning or solving problems. They may also have difficulties with language. They may not be able to remember the names of objects or have increasing trouble finding the right word. CBS overlaps with frontotemporal dementia, and people might show similar behavioural symptoms.

CBS is caused by damage to cells on the surface of the brain, called the cortex, and a deep part of the brain called the basal ganglia.

We don’t know what damages the cells and causes them to die, but a number of different proteins may play a part. A protein called tau is most frequently involved. This protein occurs naturally in the brain, but it is usually broken down before it reaches high levels. In CBS, it isn’t broken down properly and forms harmful clumps in brain cells. This can cause the symptoms a person experiences.

There is no single test to diagnose CBS. Doctors will first try to rule out other conditions with similar symptoms, such as Parkinson’s disease. They may do this using a brain scan and memory and thinking tests.

There is no specific treatment available for CBS. Some people may be prescribed medication to help with muscle spasms, pain, or sleep. Physiotherapy and speech therapy can also be beneficial in some cases.

Due to the similarities between CBS and progressive supranuclear palsy (PSP), the PSP Association provides advice and support for people with CBS. Contact their helpline on 0300 0110 122 or email

Progressive supranuclear palsy (PSP)

PSP is thought to affect over 4,000 people in the UK, or roughly 5 people in every 100,000. It is caused by an abnormal build-up of tau protein, one of the proteins that is also involved in Alzheimer’s disease.

PSP affects eye movement and leads to problems with balance and walking. Some people with PSP experience personality changes, have difficulty swallowing and develop problems with speech and vision. It commonly overlaps with frontotemporal dementia.

PSP can be difficult to diagnose because the early symptoms can be similar to other conditions, such as Parkinson’s disease. There is no specific test for PSP, but doctors may use brain scans and memory and thinking tests to help make a diagnosis.

PSP gets progressively worse and there is currently no specific treatment or cure. Some people may be prescribed medication to help with stiffness and movement. Physiotherapy, speech therapy, walking aids and wearing special glasses may also help.

The PSP Association is a charity that provides advice about living with PSP, and support to help people cope with the emotional impact of the condition. Contact their helpline on 0300 0110 122 or email

Huntington’s disease

Huntington’s disease may appear at any age, but usually develops between the ages of 30 and 55. It is thought that around 12 people in every 100,000 are living with the condition in the UK.

The condition is caused by a faulty gene. People who inherit the gene will develop Huntington’s, and their children have a 50% chance of developing the disease too. Genetic testing is available on the NHS for people with a family history. For people with symptoms of Huntington’s disease, their GP will refer them to a specialist who will carry out some tests to rule out other conditions. A blood test may also be carried out to check for the Huntington’s disease gene.

The symptoms of Huntington’s disease include involuntary movements, personality changes, thinking problems and mood swings. These symptoms will get worse over time.

The brain changes that occur in Huntington’s can sometimes cause dementia. People with dementia in Huntington’s disease generally have problems with attention, planning and problem solving. Short-term memory is often not affected until the later stages of the disease.

Although there is no cure for the condition, there are several medications, care strategies and cognitive therapies that can help to manage symptoms.

The Huntington’s Disease Association provides help and support to people affected by Huntington’s disease. Call 0151 331 5444 or email

Creutzfeldt-Jakob disease (CJD)

CJD is a very rare disease affecting no more than two in a million people in the UK per year. It is caused by a type of abnormal protein, called a prion. The prion proteins clump together and cause brain cells to die, resulting in sponge-like brain tissue. People with CJD may experience problems with memory and vision, personality changes, loss of balance and find muscle coordination harder. Jerky involuntary movements may also occur.

Although it can take some time for the symptoms of CJD to start to appear, once they do, the decline is usually far quicker than in other types of dementia. Sadly, most people with CJD will die within a year of their symptoms appearing,.

There are different types of CJD:

  • Sporadic CJD is the most common and develops spontaneously, for no known reason. In the UK, sporadic CJD usually starts in a person’s 60s.
  • Familial CJD develops because a person has inherited certain faulty genes from one of their parents. Typically, the disease starts between 30 and 55 years old.
  • Acquired CJD, also known as variant CJD, can happen when someone comes into contact with abnormal prion protein, for example by eating meat from a cow that had bovine spongiform encephalopathy (BSE or ‘mad cow disease’). The average age of symptoms of acquired CJD is 26 years and there have been only 178 confirmed cases in the UK between 1970 and 2017. These cases are extremely rare since measures to remove infected animals from the food chain came into force.


Diagnosing CJD can be difficult, and doctors will often need to perform tests such as MRI brain scans or take a sample of spinal fluid using a lumbar puncture.

There is no cure for CJD; current treatments aim to making the person as comfortable as possible.

The CJD Support Network offers support for people who have been affected by CJD. Contact their helpline on 0800 774 7317 or email

HIV-related cognitive impairment

HIV (human immunodeficiency virus) is an infection that weakens the body’s immune system. Around 105,000 people in the UK are thought to be living with HIV.

Antiretroviral drugs for the treatment of HIV have improved significantly in recent years. This means that the number of adults who progress to have AIDS (acquired immunodeficiency syndrome) has fallen dramatically. Because of this, there has also been a fall in the rate of HIV-associated dementia.

Long-term HIV can compromise brain function and lead to HIV-associated neurocognitive disorder (HAND). Approximately three in 10 people with the HIV infection, who do not have normal symptoms (called asymptomatic HIV), show some signs of mild neurological problems. HIV-related cognitive impairment symptoms can include emotional changes, depression and problems with attention and memory.

The Terrence Higgins Trust provides information, advice and support for people affected by HIV and their families. Call 0808 802 1221 or email

women together


The thyroid gland produces hormones that regulate the energy demands of every cell in the body. These hormones affect our metabolism, which is the process by which our body turns the food we eat into energy.

Hypothyroidism, otherwise known as an underactive thyroid, is a disorder in which the thyroid gland stops producing enough hormones. The condition is thought to affect two in 100 people in the UK, and is 10 times more common in women than men.

Hypothyroidism can give rise to many different symptoms, although some people do not experience any. Common symptoms of hypothyroidism include tiredness, increased sensitivity to the cold, weight gain, dry and scaly skin, and constipation.

Hypothyroidism can also give rise to dementia-like problems such as impaired memory, slower thinking, balance problems and difficulty concentrating. However, these symptoms can usually be reversed with the right treatment.

If you seek advice from a doctor because of memory problems, they can run a blood test to check whether your thyroid is working properly. This will help them decide if it is the cause of your symptoms. It is important to seek medical advice if you are concerned about yourself or someone you know.

The British Thyroid Foundation provides information and support on their website for people affected by thyroid problems.

Multiple sclerosis (MS)

Multiple sclerosis is a neurological condition affecting the brain and spinal cord. The condition is thought to affect over 100,000 people in the UK. It causes damage to the white matter in the brain,, which is made up of nerve fibres covered by a protective layer of fat called myelin. In MS, the immune system attacks the myelin, exposing the nerve fibres which affects the way they work.

The symptoms of MS can vary a lot. Some people with MS experience memory and thinking problems similar to those experienced by people with dementia.

Though there is currently no cure for MS, there are various treatments available depending on the stage of the disease and the specific symptoms someone has.

The  MS Society runs a helpline that provides information and support to people affected by MS. Contact them on 0808 800 8000 or email


Niemann-Pick disease type C

Niemann-Pick disease type C is thought to affect one in 120,000 people in the UK. It is a rare, inherited condition that prevents cholesterol and other fats from moving around the body properly. This leads to a build-up of fat inside cells in the liver, spleen, and brain.

Signs of the disease can appear at any time in children or young adults and differ from person to person. Symptoms include learning difficulties, problems with walking, swallowing and speech, an enlarged liver or spleen, and dementia.

There is no cure for the disease, but some people find certain therapies and medications helpful to manage the symptoms.

Niemann-Pick UK provides advice and support to families affected. Contact them on 0191 415 0693 or email

Normal pressure hydrocephalus (NPH)

Normal pressure hydrocephalus occurs when cerebrospinal fluid, the substance that circulates around the brain and spinal cord, begins to build up abnormally in the brain’s ventricles. The ventricles are hollow, fluid-filled spaces. As they enlarge, they can damage the surrounding brain tissue.

In most cases there is no obvious cause, and this is known as idiopathic NPH. However, the condition can arise as a result of bleeding on the brain, head injury or meningitis.

Symptoms can include difficulty walking, incontinence, and problems with thinking. NPH can be difficult to diagnose because the symptoms overlap with other neurodegenerative conditions.

In many cases, NPH can be treated with surgery. A shunt (fine tube) is inserted into one of the ventricles in the brain to drain the excess fluid and reroute it to another part of the body, usually the abdomen.

Shine is a charity that helps individuals and families affected by NPH and related conditions. For more information call 01733 555988 or email

Vitamin B12 deficiency

Vitamin B12 deficiency is thought to affect around six in 100 people under 60 years old and around 20 in 100 older people in the UK. Low levels of vitamin B12 can lead to a variety of symptoms, including numbness and tingling in the limbs, lack of coordination, unsteadiness, and vision problems. If a vitamin B12 deficiency is left untreated it can also cause dementia-like symptoms.

Some people are unable to absorb vitamin B12 due to certain genetic disorders, medical conditions such as pernicious anaemia, or as a result of taking prescription drugs like metformin.

People who limit consumption of meat and dairy, for example vegetarians and vegans, may not get enough B12 through their diet. Common sources include meat, eggs, and dairy. Alternative sources include some soy products and fortified breakfast cereals-.

Many people can be effectively treated with changes to their diet, injections or supplements of vitamin B12. If diagnosed and treated early, the symptoms of B12 deficiency are reversible.

The Pernicious Anaemia Society provides support, help and information to those affected. Contact their helpline on 01656 769717

Alcohol related cognitive impairment

Long-term, moderate to heavy alcohol consumption can have a negative effect on brain function, memory, and our ability to process information. Research has found that excessive alcohol consumption may cause the brain to shrink and become damaged.

Long-term, heavy drinkers are at risk of developing irreversible alcohol-related brain syndromes, such as Wernicke-Korsakoff syndrome.

Wernicke-Korsakoff syndrome

Wernicke-Korsakoff syndrome (WKS) is a form of dementia most commonly brought on by long-term alcohol abuse. It often follows an episode of Wernicke’s encephalopathy, a medical emergency caused by a sudden lack of thiamine (vitamin B1).

The symptoms of WKS include difficulties with balance, confusion, and memory problems. People may also spontaneously make things up to fill in the gaps in their memories, which is sometimes called confabulation.

Unlike many causes of memory problems, WKS doesn’t necessarily get worse, and symptoms can often improve after being treated with thiamine  and reducing the amount of alcohol a person drinks.

It is not clear how many people in the UK may be living with Wernicke-Korsakoff syndrome. Anyone at risk of developing this condition through alcohol misuse may wish to contact Alcohol Concern on 0300 123 1110.

This information was updated in February 2022 and is due for review in February 2024. It was written by Alzheimer’s Research UK’s Information Services team with input from lay and expert reviewers. It does not replace any advice that doctors, pharmacists, or nurses may give you. Please contact us if you would like a version with references.

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