What is corticobasal degeneration?
Corticobasal degeneration (CBD) is a rare condition where brain cells become damaged over time and certain sections of the brain start to shrink.
CBD is a progressive condition. This means that the initial symptoms will become more severe over time, and new symptoms may also develop.
Initial symptoms of CBD include:
- sudden difficulties in controlling certain limbs
- loss of balance and co-ordination (the medical term for this is ataxia)
As the condition progresses, symptoms become more wide ranging and troublesome, such as:
- muscle spasms and stiffness
- ongoing decline of mental functions (dementia)
- difficulties swallowing food and liquid (dysphagia)
- difficulties speaking
Read more about the symptoms of corticobasal degeneration.
What causes CBD?
In CBD, brain damage occurs because a protein called tau, which is normally found in low levels in the brain, builds up and forms clumps which kill nearby brain cells.
This damages vital parts of the brain (such as the cortex and the basal ganglia) that are responsible for important functions including:
- higher thought processes such as planning and understanding
It is not known exactly why there is an excess of tau protein that forms clumps.
Read more about the causes of corticobasal degeneration.
There is no cure for CBD. Several medications, such as memantine, have been suggested to slow the progression of CBD symptoms and improve the function of the brain, but it is still unclear how effective they are.
Most treatments for CBD focus on relieving symptoms and helping people cope better with daily life. These include medication to relax muscles and using feeding tubes to overcome difficulties swallowing.
Read more about treating corticobasal degeneration.
Who is affected?
CBD is a rare condition.
It is difficult to know exactly how many people are affected as it is often misdiagnosed as another condition, such as a stroke or progressive supranuclear palsy, which share similar symptoms.
It was recently estimated that 1 person in 20,000 is living with CBD.
CBD mostly affects people who are 60 to 80 years old. It may be more common in women than in men, but because the condition is so rare, it is difficult to be certain.
The number of reported cases of CBD has risen sharply in the last twenty years. It is unclear whether this is due to CBD becoming more widespread or because doctors are better at diagnosing the condition.
Although CBD itself isn’t life-threatening, it can lead to serious complications. One of the most common complications is difficulty swallowing (dysphagia), which can cause a person to choke or inhale food or liquid into the airway (aspiration). Aspiriation can develop into pneumonia, which can be fatal.
Read more about the complications of CBD.
Most people with CBD will not live longer than ten years after symptoms start.
Symptoms of corticobasal degeneration
Corticobasal degeneration (CBD) is a progressive condition. This means that the symptoms develop gradually, before becoming more severe over many years.
However, it is important to realise that only a few people will experience all the symptoms outlined below. Also, individual symptoms can vary in severity from person to person.
The most common initial symptom of CBD is a sudden difficulty controlling one of your limbs. In most people, this is usually their hand or arm, but sometimes a person’s leg can be affected.
You may have muscle stiffness, rigidity and spasms in your limb, and you will probably find it increasingly difficult to use the affected limb. Some people with CBD have reported that it feels like the affected limb is no longer under their control, and does not belong to them. This is known as alien limb syndrome.
Another common initial symptom of CBD is that you begin to lose your sense of balance and co-ordination, which leads to walking difficulties.
As CBD progresses, it will affect other limbs, usually in both your arms and legs.
Balance and co-ordination will get worse and many people find it increasingly difficult to walk. Most people will have problems with their speech, which will become slow and slurred, making it difficult to understand.
Eye muscles are usually also affected. Many people have problems moving their eyes up and down and, less commonly, to the left and right. This can increase the risks of falls and cause problems carrying out everyday tasks, such as eating and reading.
At this stage, many people with CBD start to have symptoms of dementia, including:
- problems recalling words and expressing yourself using the correct language
- short-term memory loss and increasing forgetfulness
- problems doing tasks that require planning
- problems coping with sudden and unexpected situations, such as suddenly realising that you have forgotten the keys to your house
It is also common for someone with CBD to experience personality changes and become depressed, apathetic, irritable, agitated or anxious.
A small number of people with CBD also develop obsessive compulsive disorder (OCD).
As CBD reaches an advanced stage, the symptoms of muscle stiffness and rigidity will continue to get worse, and you may lose the ability to move one or more of your limbs. Some people with advanced CBD are unable to walk and need a wheelchair.
The quality of your speech will probably continue to deteriorate and people may have difficulty understanding you.
Problems controlling your eye muscles are also likely to get worse. Some people with advanced CBD will not be able to change the direction of their gaze and will only be able to stare straight ahead.
For a small number of people with advanced CBD, dementia will worsen and they will require constant care.
Most people with advanced CBD will find it increasingly difficult to swallow food and liquid. This is known as dysphagia. At some point, people with CBD will need to consider the possible benefits and drawbacks of using a feeding tube.
As a result of dysphagia, many people with CBD will experience repeated chest infections caused by fluids or small particles of food that inadvertently fall down into their lungs. This can lead to a serious condition called aspiration pneumonia, which is the leading cause of death in cases of CBD.
Read more about aspiration pneumonia.
Corticobasal degeneration causes
Cortiocobasal degeneration (CBD) is caused by a progressive loss of brain cells. This shrinks parts of the brain responsible for movement, speech and higher thought processes, such as understanding and planning.
Researchers have found that the damage is caused by a protein called tau. Tau is found in low levels in healthy brains. But in CBD, the levels of tau protein increase, forming clumps that are thought to kill nearby brain cells.
CBD has similar symptoms to another condition called progressive supranuclear palsy (PSP). However, in PSP the pattern of brain damage is slightly different. It's possible that both CBD and PSP are two related syndromes that have the same underlying causes.
It is not known what leads to the over-production of the tau protein and the resulting death of brain cells.
One theory is that CBD could be the result of a mutation in the gene responsible for producing the tau protein. This is known as the MAPT gene (microtubule-associated protein tau gene).
A genetic mutation happens when the instructions found in all living cells become scrambled in some way. This leads to one or more of the processes in the body not working as it should.
Read more about genetics.
There is evidence the genetic mutations affecting the MAPT gene are responsible for conditions with similar symptoms, such as some types of dementia and progressive supranuclear palsy.
However, there is still no hard evidence to support the theory that mutations in the MAPT gene are responsible for CBD.
Also, as CBD does not run in families, it would appear that the condition is not wholly caused by the genes a person inherits from their parents.
One or more environmental factors may trigger the onset of CBD in people who are susceptible to it.
Possible factors could be:
- an as yet unidentified virus or other type of infectious agent, which may slowly infect the brain over many years
- an unidentified neurotoxin (a poison that damages the brain and nerve cells) that may be present in the environment
Corticobasal degeneration diagnosis
No single test can be used to diagnose corticobasal degeneration (CBD).
Instead, the diagnosis is based on the type and pattern of symptoms and ruling out other conditions that can cause similar symptoms, such as a stroke, Parkinson’s disease, motor neurone disease and more common types of dementia.
Because CBD shares symptoms with many other more common conditions, confirming the diagnosis can be challenging and may take several months or, in some cases, years.
If you have symptoms that suggest that there is something wrong with your brain, it is likely that you will be referred for brain imaging studies.
These may include:
- a magnetic resonance imaging (MRI) scan – strong magnetic fields are used to produce a detailed image of the inside of the brain
- a positive emission tomography (PET) scan – similar to an MRI scan, a PET scan has the added advantage that it can assess how different parts of the brain are functioning
These types of imaging studies can be useful in ruling out other possible causes, such as a brain tumour and stroke.
They can also detect abnormal changes to the brain that are consistent with a diagnosis of CBD, such as shrinkage in the cortex and basal ganglia.
Ruling out Parkinson’s disease
You may also be prescribed a medication called levodopa. This can help determine whether your symptoms are caused by CBD or Parkinson’s disease.
This is because people with Parkinson’s disease usually experience a marked improvement in their symptoms after taking levodopa. However, this is not the case for people with CBD, and levodopa usually only has a limited effect in improving symptoms.
It is also likely that you will be referred to a neurologist (nerve and brain specialist) for neuropsychological testing.
This involves having a series of tests that are designed to evaluate the full extent of your symptoms and their impact on your mental abilities.
The tests will look at abilities such as:
- ability to understand language
- the ability to process visual information, such as words and pictures
Most people with CBD have a distinct pattern in terms of their mental abilities.
They have poor concentration, a low attention span and problems with spoken language and processing visual information.
Their memory of previously learned facts, such as who was the last prime minister, is usually unaffected.
Receiving the diagnosis
Once all other possible causes of symptoms have been ruled out, a confident diagnosis of CBD can usually be made.
Being told that you have CBD can be an emotionally devastating experience, and the news can often be difficult to take in. Therefore, at this time, it is important that you have the support of your family and care team, who will be able to help you come to terms with the diagnosis.
A charity called the PSP Association provides help and support for people with CBD. The charity mainly helps people with progressive supranuclear palsy (PSP), but as the symptoms and treatments of CBD and PSP are similar, the PSP Association also supports people with CBD.
As your symptoms progress, you will require full-time care and most likely assistant technology, such as a wheelchair, to help with activities.
Corticobasal degeneration treatment
Corticobasal degeneration (CBD) is a rare condition, so you will probably be referred to a specialist centre that has experience in CBD, such as the Institute of Neurology in London.
After discussion with the staff, a treatment plan for your care should be drawn up. The plan will probably involve:
- providing relief from the symptoms of CBD when possible
- giving you support and advice to make your life easier
Your care team
As CBD can have an impact on many different aspects of your life and health, treatment is provided by a team of health and social care professionals working together. This is known as a multidisciplinary team (MDT).
Members of your care team may include:
- a neurologist – a specialist in treating conditions that affect the nervous system
- a physiotherapist – a therapist who helps people improve their co-ordination and range of movement
- a speech and language therapist
- an occupational therapist – a therapist who helps people improve the skills and abilities they need for daily activities, such as washing or dressing
- a psychologist
- a social worker – they will be able to advise you about the support available from social services
- an ophthalmologist or orthoptist – specialists in treating eye conditions
- a palliative care specialist – a healthcare professional who specialises in treating people with terminal conditions
- a specialist neurology nurse – they will usually be your first point of contact with the rest of the team
While there is no medication to treat CBD directly, there are some medications that can help control some of the condition’s symptoms. These are described below.
Memantine is a type of medication known as an NMDA antagonist, which was designed to treat Alzheimer’s disease. It helps reduce abnormal brain activity, which helps slow the progression of Alzheimer's disease and improves mental and physical functions.
Some experts have suggested that memantine may have a similar effect in people with CBD.
There is limited evidence that memantine is effective or safe in people with CBD. Therefore, you should discuss the potential pros and cons of treatment with memantine (or possibly other medications used to treat Alzheimer’s disease) with your care team.
Side effects of memantine include:
- shortness of breathe
Levodopa is a medication that is often used to treat Parkinson’s disease. While it is usually less effective for people with CBD, it may provide short-term improvement in muscle stiffness and rigidity in some people.
Levodopa works by increasing the levels of a brain chemical called dopamine, which transmits messages from your brain that control and co-ordinate your body’s movements. Therefore, an increase in dopamine levels may lead to a corresponding improvement in muscle control.
Common side effects of levodopa are:
However, these side effects usually pass within a few weeks, once your body becomes used to the medication. Other side effects can occur if you take levodopa on a long-term basis and include:
- involuntary physical movements, such as jerking
- mood changes – for example feeling more anxious
Baclofen is a type of medication that can be used to treat muscle stiffness and rigidity. It works by blocking some of the nerve signals that cause muscle stiffness.
Side effects of baclofen may include:
- an increased need to urinate
These side effects usually pass once your body becomes used to the medication.
Clonazepam is a type of medication that can be used to treat symptoms of muscle spasms.
Side effects of clonazepam may include:
- muscle weakness
- loss of co-ordination
As with baclofen, the side effects of clonazepam usually pass once your body has become used to the medication.
You should avoid drinking alcohol while you are taking clonazepam because it can make the side effects worse, as well as magnifying the effects of the alcohol.
A physiotherapist can give you advice about how to make the most of your remaining mobility by using exercise. Regular exercise can help strengthen your muscles, improve your posture and prevent stiffening of your joints.
Your physiotherapist will also be able to give you advice about any aids that could help you, such as a walking frame or shoes designed to reduce your risk of slipping and falling.
Cognitive stimulation is a type of therapy that is used to treat the symptoms of dementia. It involves taking part in activities and exercises that are designed to improve your memory, problem-solving skills and language ability.
Cognitive stimulation is provided by a trained carer and usually consists of two 45-minute sessions a week. During these sessions, you will be involved in discussions about a variety of topics, as well as taking part in word and memory games, and other activities, such as identifying pictures of famous people.
An occupational therapist (OT) can provide advice about the best ways to increase your safety and prevent trips and falls during your day-to-day activities.
For example, many people with CBD benefit from having bars placed along the sides of their bath to make it easier to get in and out.
The occupational therapist will also be able to spot potential hazards in your home that could lead to a fall, such as poor lighting, badly secured rugs and crowded walkways and corridors.
Speech and language therapist (SLT)
A speech and language therapist (SLT) can help improve your speech and swallowing problems. They can also teach you a number of techniques to make the most of your speech function by making your voice as clear as possible.
As CBD progresses, you may need some sort of assistive technology to help you communicate. A range of communication aids is available, and your SLT will be able to advise you about the devices that will be most suitable for you.
Your SLT should also be able to help you if you have difficulties swallowing food and water (dysphagia).
For example, they should be able to teach you exercises to help stimulate the nerves that are used to trigger your swallowing reflex and strengthen the muscles that are used during swallowing.
A number of physical techniques can also be used to make swallowing easier. For example, some people find that moving their chin forward while swallowing helps prevent any food from entering their airways.
Diet and severe dysphagia
As the symptoms of your dysphagia become more severe, you will require additional treatment to compensate for your swallowing difficulties.
You may be referred to a dietitian. They will advise you about making changes to your diet, such as incorporating food and liquids that are easier to swallow while ensuring you receive a healthy, balanced diet.
For example, mashed potatoes are a good source of carbohydrates, while scrambled eggs and cheese are high in protein and calcium.
Feeding tubes may be recommended in severe cases of dysphagia that increase your risk of developing malnutrition and dehydration. You should discuss the pros and cons of feeding tubes with your family and care team, preferably when your symptoms of dysphagia are at an early stage.
There are two types of feeding tubes:
- nasogastric tube – a tube is passed down your nose and into your stomach
- percutaneous endoscopic gastrostomy (PEG) tube – a tube is surgically implanted directly into your stomach, which passes through a small incision on the surface of your stomach or abdomen
Nasogastric tubes are designed for short-term use and last for 10–28 days before they need to be replaced. PEG tubes are designed for long-term use and last for up to six months before they need to be replaced.
Many people with CBD draw up an advanced directive. An advanced directive is where you make your treatment preferences known in advance in case you cannot communicate your decisions later because you are too ill.
Issues that can be covered by an advanced directive include:
- whether you want to be treated at home, in a hospice or in a hospital once you reach the final stages of CBD
- what type of painkillers you would be willing to take
- whether you would be willing to use a feeding tube if you were no longer able to swallow food and liquid
- whether you are willing to donate any of your organs once you die (the brains of people with CBD are particularly useful for ongoing research)
- if you experience respiratory failure (loss of lung function) due to aspiration pneumonia, whether you would be willing to be resuscitated by artificial means, such as having a breathing tube inserted into your neck
Your care team will be able to provide you with more information and advice about advanced directives.
Complications of corticobasal degeneration
One of the most potentially serious complications of corticobasal degeneration (CBD) is aspiration pneumonia.
Aspiration pneumonia is a lung infection that is triggered when a small piece of food enters the lungs.
People with CBD are particularly vulnerable to aspiration pneumonia. This is because their impaired swallowing reflexes mean that their larynx (voice box) does not close during swallowing, so their lungs are not protected.
The symptoms of aspiration pneumonia include:
- high temperature (fever) of 38C or above
- chest pain
- shortness of breath
- blue skin (cyanosis), due to a lack of oxygen
You may also have a cough that sometimes produces foul-smelling phlegm and may contain traces of blood and pus.
Contact your care team immediately if you are being treated for CBD and you develop these symptoms. If this is not possible, contact your local out-of-hours service, or call NHS Direct on 0845 4647.
The symptoms of aspiration pneumonia can range from mild to severe. Severe cases will require admission to hospital and treatment with intravenous antibiotics.
In particularly vulnerable or frail people, there is a chance that the infection could lead to their lungs becoming filled with fluid, preventing them from working properly. This is known as acute respiratory distress syndrome (ARDS).
As most people with advanced CBD are vulnerable and frail, repeated episodes of aspiration pneumonia often result in ARDS and then death.