What are the rare forms of dementia?

This post is on the rarer forms of dementia, which make up the minority of dementia diagnoses. These also include reversible and treatable dementias, such as those resulting from infectious diseases or nutrition deficiencies. As Alzheimer’s disease is the most commonly diagnosed form of dementia, it receives the majority of focus in awareness raising, research, and funding for treatment and prevention. This can leave those with the rarer forms of dementia without much information on their dementia type or options for treatment, fewer disease-specific support options, and feeling frustrated and isolated. My hope is that this post will be informative and raise your awareness on other types of dementia that individuals and families face.  

A bit of information on reversible dementias from a 2009 research article in the Indian Journal of Psychiatry:

The reported frequency of dementia due to potentially reversible causes varies from 0 to 23%. Commonest among these causes are alcohol and medication related dementia, depression induced cognitive impairment, surgical brain lesions such as normal pressure hydrocephalus [NPH], tumors and chronic subdural hematomas, metabolic disorders such as hypothyroidism, hypoparathyroidism, vitamin B12 deficiency and central nervous system (CNS) infections such as neurosyphilis and HIV. The Indian study by Srikanth found reversible causes, especially neuroinfections and vitamin B12 deficiency to account for 18% of all dementias.

This first section of information largely comes from Alzheimer Europe. The second section comes from Alzheimer’s Society and provides more detailed information on symptoms and treatments.

This first set of information is based on the results of the Alzheimer Europe project “Rare forms of dementia” which was financed in the framework of the rare diseases programme of the European Commission. Rare diseases are described by the European Community Action programme as diseases of low prevalence “which is generally recognised as less than 5 per 10 000 in the Community”

While quite extensive work has been carried out on the prevalence of dementia, the same cannot be said for the various forms of dementia, which are covered in this report and for which epidemiological data are often either incomplete or missing. This presented us with an obvious problem at the outset of our project, in order to decide on which forms of dementia we should include and which fulfilled the criteria set out by the European Commission.

It is clear that dementia in itself is not a rare phenomenon under the Commission definition and neither are the two most frequent causes of dementia, Alzheimer’s disease or vascular disease. It it is far more difficult to find a breakdown of the various diseases covered by the definition of dementia. Often the percentages used vary quite considerable.

Alzheimer’s disease is considered to be the main cause of dementia and according to research, should amount to between 50 and 75% of all cases. Vascular dementia is the second most common form of dementia and it is generally accepted that it accounts for between 25 and 50% of all cases of dementia.

For the purpose of our report, we have therefore concluded that all other forms of dementia account for maximum 25% of all forms of dementia, which would give us a prevalence rate of 31.25 per 10 000.

Fronto-temporal degeneration and Lewy body diseases would be the commonest of these rarer forms of dementia and it is generally accepted that they account each for about 5% of all cases of dementia or 7.81 per 10 000. Both of these categories though cannot be considered as one single disease, but rather as a spectrum of different diseases, which would individually fall under the Commission definition of “rare diseases”

Similarly, all other causes of dementia are even rarer and have been included in our report, as well as the rare forms of both Alzheimer’s disease and vascular dementia.

We found some 30 diseases or disease groups which are either rare in themselves or which lead to dementia in rare cases. For each disease we provide general outline, describe the symptoms and course, the causes and risk factors, the genetics, the frequency, the diagnostic procedures, as well as information on care and treatment, ongoing research and available services.

The expert group discussed possible ways on how to present these diseases and we ultimately opted for a classification system based on the causes of dementia, as this system had the advantage of grouping related diseases.

The biggest group of diseases is made up of degenerative diseases , which are characterised by a progressive loss of nerve cells and synapses. For most of these diseases, the causes of this nerve loss are unknown and our knowledge about possible treatment or prevention remains limited. Thse would include:


Infectious diseases are caused by an infectious agent, such as a virus or prion. These would include:

Metabolic diseases are a group of often treatable diseases which may lead to dementia and which are caused by an under-activity or over-activity of a part of the human metabolism. These would include:


Traumatic diseases are caused by a trauma and in the disease described in this report by repeated head trauma. These would include:

  • REPEATED HEAD TRAUMA (Chronic traumatic brain injury associated with boxing – dementia pugilistica – occurs in approximately 20 % of professional boxers.)

You can also read my post on boxing and dementias here, and on American football and other sports and dementias here, and my post on how 95% of NFL players have brain injury here. You can also read my post about a soldier who suffered head trauma due to an explosion and later developed dementia here.


Toxic diseases are caused by the consumption of substances, which are harmful to the human body. These would include:

  • WERNICKE-KORSAKOFF SYNDROME (WKS) (The main cause of Wernicke-Korsakoff syndrome is chronic alcohol abuse which results in severe deficiency of the vitamine thiamine (vitaminE B1). Total population figures for the prevalence have proved very difficult to estimate; in the Hague, The Netherlands has an estimated prevalence of 48 per 100 000 of the total population and in Queensland, Australia, estimated incidence is 6.5 per 100 000 new cases each year.)
  • HEAVY METAL POISONING (Exposure to heavy metals, such as arsenic, mercury, aluminum, lithium, or lead, can cause cognitive decline, particularly after acute exposure.)


Cerebrovascular diseases are diseases of the blood vessels in the brain, which are the second most common cause for dementia. These would include:

  • CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy. Prevalence is less than 1 in 100 000)
  • BINSWANGER DISEASE (also known as Subacute arteriosclerotic encephalopathy)
  • CEREBRAL AMYLOID ANGIOPATHY (CAA) (CAA at a subclinical level can occur in up to 98% of AD and 85% of aged brains.)


Other rare causes of dementia include:

You can also read my post on the link between MS and dementia here and my post on normal pressure hydrocephalus and dementia here.

The rest of this information comes to us from Alzheimer’s Society, the UK’s leading dementia support and research charity for people living with dementia, their families, and care partners. And also one of my favorite sites to find news and information on Alzheimer’s disease and other dementias.

Alzheimer’s disease is the most common cause of dementia, but there are many rarer diseases and conditions that can lead to dementia, dementia-like symptoms or mild cognitive impairment. Rarer forms of dementia account for only around 5% of all dementia cases in the UK. This factsheet outlines some of these rarer causes and gives some suggestions for where to go for more specialist advice and information.

This factsheet covers the following rarer causes of dementia:

  • corticobasal degeneration (CBD)
  • Creutzfeldt-Jakob disease (CJD)
  • HIV-associated neurocognitive disorder (HAND)
  • Huntington’s disease
  • multiple sclerosis (MS)
  • Niemann-Pick disease type C
  • normal pressure hydrocephalus (NPH)
  • Parkinson’s disease dementia (PDD)
  • posterior cortical atrophy (PCA)
  • progressive supranuclear palsy (PSP).

Being told that you or a loved one has dementia can be very difficult and you may experience a range of different emotions as time goes on. Support is available if you need it. Alzheimer’s Society’s National Dementia Helpline (0300 222 11 22) can provide information, support, guidance and signposting to other organisations.

Corticobasal degeneration

Corticobasal degeneration (CBD) is a rare disease in which parts of the brain become damaged and begin to shrink. The outer layer of the brain, known as the cortex, and deep parts of the brain, called the basal ganglia, are both affected. It is not yet known what causes CBD but producing too much of an abnormal form of a protein called tau is thought to play a role. The disease usually affects people between the ages of 60 and 80.

The first symptoms that people with CBD experience are problems with movement, such as stiffness and jerkiness in one or more of their limbs and a failure to control hand movement on one side (known as ‘alien hand syndrome’). As the disease progresses, these problems will often spread to other limbs. Many people experience symptoms of dementia, including problems with memory and thinking. A small proportion of people with frontotemporal dementia also develop CBD as an ‘overlapping’ condition. Other symptoms of CBD include loss of balance and co-ordination, and difficulties speaking and swallowing.

Currently, there is no cure or treatment available to slow the progression of CBD, but drugs may help some symptoms and physiotherapy, occupational therapy and speech and language therapy may be beneficial. On average, people live for around eight years after their symptoms first appear.

For further information and support contact the Frontotemporal Dementia Support Group (see ‘Other useful organisations’).

You can also read my post about CBD here and my post about Frontotemporal dementia here.

Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) is caused by an abnormally shaped protein called a prion infecting the brain. Sporadic CJD, which normally affects people over 40, is the most common form of the disease. It is estimated that the disease affects about one out of every 1 million people each year. It is not known what triggers sporadic CJD, but it is not known to be inherited or otherwise transmitted from person to person.

A more recently identified form of CJD, called new variant CJD, was caused by eating meat from cattle infected with bovine spongiform encephalopathy (BSE). This typically affected younger adults. In new variant CJD, there may be many years between a person being infected and the development of symptoms.

In sporadic CJD, the disease usually progresses within a few months. Early symptoms include minor lapses of memory, mood changes and loss of interest. Within weeks the person may complain of clumsiness and feeling muddled, become unsteady walking, and have slow or slurred speech. Symptoms progress to jerky movements, shakiness, stiffness of limbs, incontinence and loss of the ability to move or speak. By this stage the person is unlikely to be aware of their surroundings or disabilities.

People affected by CJD usually die within six months of their early symptoms developing. In a small number of patients the disease may take longer to run its course.

Diagnosis can often be difficult as a range of causes including Alzheimer’s disease and vascular dementia need to be ruled out. (See factsheets 401, What is Alzheimer’s disease? and 402, What is vascular dementia?). If no immediate diagnosis is obvious, the neurologist may conclude that the person has a rare neurodegenerative disease – a type of disease that affects the nervous system and gets worse over time – and may refer them to the National Prion Clinic in London for further assessment (see ‘Other useful organisations’).

There is no known cure for CJD, however it is an area which is being actively researched.

You can also read my post about CJD here.

HIV-associated neurocognitive disorder (HAND)

HIV (human immunodeficiency virus) causes an infection that weakens the immune system, making it harder for the body to fight infections and disease. HIV infection can cause a number of different problems in the brain, which affect up to half of people with HIV. This is known as HIV-associated neurocognitive disorder (HAND).

Difficulties with memory, thinking and reasoning (aspects of cognition) are common with HIV, but they are usually mild and dementia is much rarer. Before the use of antiretroviral drugs (medication that helps to control HIV), around 20-30 per cent of people with advanced HIV infection previously developed dementia. This figure has now decreased to around 2 per cent.

Neurocognitive disorders in people with HIV may be caused by the virus directly damaging the brain. They may also be the result of a weakened immune system enabling infections and cancers to attack the brain.

Symptoms may include problems with short-term memory, learning, speed of thinking, difficulties with concentration and decision making, unsteadiness and mood changes. People may also have problems with their sense of smell.

Some people with HIV may experience only a few very mild symptoms, such as a decline in the ability to think quickly or clearly. These mild impairments do not amount to dementia.

HIV is easily overlooked as a possible cause of dementia. Even when someone is known to have HIV infection, cognitive impairment can sometimes be difficult to diagnose. This is because the symptoms are similar to those of other conditions, such as depression.

Treatment with a combination of at least three antiretroviral drugs often prevents cognitive impairments worsening and, for many people, can reverse the cognitive damage caused by HIV. Rehabilitation programmes may also help people with HAND to re-learn skills.

The Mildmay Hospital provides holistic inpatient and day care services for people with HAND (see ‘Other useful organisations’).

You can also read my post about HAND here.

Huntington’s disease

Huntington’s disease is an inherited disease causing abnormal movements and problems with coordination. Other symptoms include mood problems and cognitive impairment that gets progressively worse over time. The age of onset and the course of the disease varies for each person, and dementia can occur at any stage of the illness.

Symptoms of dementia associated with Huntington’s disease mainly include difficulties with concentration, planning and organisational skills. A loss of short-term memory may also occur. People with Huntington’s disease may also develop obsessive behaviour. This form of dementia differs from Alzheimer’s disease in that those affected continue to recognise people and places until the very late stages of the illness.

At present, there is no cure for dementia associated with Huntington’s disease, but research is being carried out to try to find treatments for the future.

For more information contact the Huntington’s Disease Association (see ‘Other useful organisations’).

You can also read my post about Huntington’s disease here.

Multiple sclerosis

Some people with multiple sclerosis (MS) experience a loss of some of their mental abilities. This happens if damage caused by the MS occurs in certain parts of the brain. People may be affected to different degrees, and in different ways, over a period of time. The mental abilities most likely to be affected are memory, concentration and problem solving. They may also experience emotional problems, such as mood swings and personality changes.

The term ‘dementia’ is not generally used in association with multiple sclerosis because the decline is not usually as severe as it is in other forms of dementia, such as Alzheimer’s disease. It is more usual to describe the person as ‘experiencing cognitive difficulties’. For more information contact the MS Society (see ‘Other useful organisations’).

You can also read my post about how MS and dementia are related here.

Niemann-Pick disease type C

Niemann-Pick disease type C is one of a group of rare inherited disorders. It is not related to frontotemporal dementia, which is also sometimes called Pick’s disease. It mainly affects school-age children but can occur at any time, from early infancy to adulthood. It is caused by an inherited inability to deal with cholesterol and other fats, causing them to accumulate in cells, including those in the brain. This can lead to progressive loss of movement and difficulties with walking and swallowing.

People who first show symptoms in late adolescence or early adulthood are more likely to experience dementia as part of the disease. The dementia symptoms include confusion, memory problems and difficulties in concentrating and learning.

There is currently no treatment for the disease, and life expectancy varies. However, researchers have identified the responsible gene and there is continuing research into this area. For further information and support contact the Niemann-Pick Disease Group (see ‘Other useful organisations’).

You can also read my post on Niemann-Pick Disease here and my post about a young girl with this rare disease and her dementia.

Normal pressure hydrocephalus

Normal pressure hydrocephalus occurs when excess fluid accumulates in the brain, but without causing pressure to build up in the brain tissue. Symptoms include difficulties with walking, dementia and urinary incontinence. In most cases the cause is unknown, but it sometimes develops after recovery from a head injury, brain haemorrhage (a bleed in the brain) or severe meningitis (an infection of the tissue surrounding the brain).

Treatment involves surgery to drain excess fluid. The success of this treatment varies depending on how early the condition is diagnosed, but symptoms may improve after surgery and some people make an almost complete recovery.

For further information and support, contact Shine (see ‘Other useful organisations’).

You can also read my post on Normal pressure hydrocephalus here.

Parkinson’s disease

People with Parkinson’s disease have a higher-than-average risk of developing dementia, although around two thirds of people are unaffected. When dementia does occur, it is typically not until late in the course of the illness. Parkinson’s disease dementia accounts for around 2 per cent of all cases of dementia in the UK.

Symptoms of dementia associated with Parkinson’s disease vary from person to person. The most common are memory loss and loss of the ability to think quickly and carry out everyday tasks. The person may become obsessive, and there may be a loss of emotional control, with sudden outbursts of anger or distress. Visual hallucinations – seeing things which are not really there – may also occur. The person’s symptoms vary and can seem better or worse at different times.

It is thought that Parkinson’s disease dementia results from microscopic deposits known as Lewy bodies, located in nerve cells in the brain stem (the lower part of the brain just above the spinal cord). As Parkinson’s disease progresses, Lewy bodies spread beyond the brain stem into other parts of the brain, causing dementia.

Lewy bodies are also seen in dementia with Lewy bodies (DLB). Parkinson’s disease dementia appears very similar to dementia with Lewy bodies. The main difference is that problems with movement occur before cognitive symptoms in dementia associated with Parkinson’s disease. In dementia with Lewy bodies, cognitive symptoms occur before, or at the same time as, problems with movement (see factsheet 403, What is dementia with Lewy bodies?).

You can also read my post on DLB here.

The side-effects of certain drugs for Parkinson’s may make symptoms of dementia worse, so adjusting a person’s medication accordingly can sometimes be of benefit. Some of the drugs used in Alzheimer’s disease may also be helpful, especially if the person is experiencing hallucinations or delusions.

For further information contact Parkinson’s UK (see ‘Other useful organisations’).

Posterior cortical atrophy

You can also read my post on PCA here.

Posterior cortical atrophy (PCA), also known as Benson’s syndrome, is a rare degenerative condition in which damage occurs at the back (posterior region) of the brain. In the vast majority of people, the cause of PCA is Alzheimer’s disease.

The first symptoms of PCA tend to occur when people are in their mid-50s or early 60s. However, the first signs are often subtle and so it may be some time before a formal diagnosis is made.

Initially, people with PCA tend to have a relatively well-preserved memory but experience problems with their vision, such as difficulty recognising faces and objects in pictures. They may also have problems with literacy and numeracy. These tasks are controlled by the back part of the brain, where the initial damage in PCA occurs.

As damage in the brain spreads and the disease progresses, people develop the more typical symptoms of Alzheimer’s disease, such as memory loss and confusion. There are no specific medications for the treatment of PCA but some people find medications for Alzheimer’s disease helpful.

For further information and support contact the Posterior Cortical Atrophy Support Group (see ‘Other useful organisations’).

Progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a rare progressive movement disorder, sometimes known as Steele-Richardson-Olszewski syndrome. It affects many areas of the brain and people typically have symptoms similar to those of Parkinson’s disease. As with Parkinson’s disease, there may be a tremor (involuntary shaking of the body and limbs), but this is much less prominent in PSP. The specific parts of the brain that are damaged include the regions that control eye movements and those that keep a person steady when they are walking, resulting in frequent falls. The cause of the damage that occurs in PSP is unknown, but is linked to abnormal deposits of a protein called tau.

PSP mainly occurs in people over the age of 60, although it occasionally affects younger people. One striking symptom is paralysis of eye movements and problems with double vision. Other symptoms include stiff or slow movements, difficulties walking and speaking, swallowing problems and personality changes.

Although the person may also have problems with their speed of thinking and memory, they will remain aware of what is going on around them. In most cases, the person is more likely to be described as ‘experiencing cognitive difficulties’ rather than ‘having dementia’. However, a small proportion of people with frontotemporal dementia also develop PSP as an ‘overlapping’ condition. There is no cure for PSP but there are medications available to help control some symptoms.

For further information and support contact the PSP Association (see ‘Other useful organisations’).

You can also read my post about PSP here.

Other useful organisations

Frontotemporal Dementia Support Group

Provides information, advice and support for people with frontotemporal dementia and their carers. Was formerly the Pick’s Disease Support Group.

T 07592 540555
E jill.walton@ucl.ac.uk
W www.ucl.ac.uk/drc/support-groups/FTD-support-Group


Huntington’s Disease Association

Association that provides information, advice, support and publications for families affected by Huntington’s disease in England and Wales. They can put you in touch with a regional adviser and your nearest branch or support group.

T 0151 298 3298
E info@hda.org.uk
W http://www.hda.org.uk/


Mildmay Hospital

Provides holistic inpatient and day care services for people affected by HIV-related cognitive impairment. Referrals must be made by other hospital or community services.

T 020 7613 6300
E info@mildmay.org
W http://www.mildmay.org/


MS Society

Charity providing information and support to anyone affected by MS. Has a national helpline and a network of over 350 local branches.

T 0808 800 8000 FREE (free helpline, weekdays 9am-9pm)
E helpline@mssociety.org.uk
W http://www.mssociety.org.uk/


National Prion Clinic

Clinic based at the National Hospital for Neurology and Neurosurgery. It provides diagnosis, care and support for patients with, or suspected of having, diseases caused by prions such as CJD.

T 020 7692 2397
E help.prion@uclh.org
W http://www.nationalprionclinic.org/


Niemann-Pick Disease Group (UK)

Not-for-profit organisation that supports and promotes research to find a cure or treatments for all types of Niemann-Pick Disease and provides support services to individuals and families affected by the disease.

T 0191 415 0693
E niemann-pick@zetnet.co.uk
W http://www.niemannpick.org.uk/


Parkinson’s UK

Charity that provides information, advice, support and publications for people with Parkinson’s disease. They can put you in touch with your nearest branch, offering information, support and social contact for people with Parkinson’s and their families.

T 0808 800 0303 FREE (helpline 9am-8pm Monday to Friday, 10am-2pm Saturday)
E hello@parkinsons.org.uk
W http://www.parkinsons.org.uk/


Posterior Cortical Atrophy Support Group

Provides information and support to people with PCA, and their families, friends and healthcare professionals.

T 07592 540 55507592 540 555
E jill.walton@ucl.ac.uk
W www.ucl.ac.uk/drc/support-groups/PCA-support-group


PSP Association

Charity that provides information and support for families affected by progressive supranuclear palsy.

T 01327 322 41001327 322 410
E psp@pspeur.org
W http://www.pspeur.org/



Charity that provides information and advice for people with hydrocephalus (and spina bifida).

T 01733 55598801733 555988
W http://www.shinecharity.org.uk/


Factsheet 442

Last reviewed: March 2015
Next review due: March 2018

Reviewed by: Professor Tony Bayer, Professor of Geriatric Medicine, Institute of Primary Care and Public Health, Cardiff University, and Dr Claudia Metzler-Baddeley, Cardiff University Brain

Research Imaging Centre, School of Psychology, Cardiff University

This factsheet has also been reviewed by people affected by dementia. A list of sources is available on request.


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