CBD - Diagnosing corticobasal degeneration

There's no single test to help 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.

As 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.

Imaging scans

If you have symptoms that suggest there's something wrong with your brain, it's likely you'll be referred for brain imaging studies.

These may include a:

magnetic resonance imaging (MRI) scan – where strong magnetic fields are used to produce a detailed image of the inside of the brain
DatSCAN – a test that involves using a small amount of radioactivity to obtain images of an area of your brain; it can help differentiate between brain disorders
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 of CBD, such as a brain tumour or 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 isn't the case for people with CBD, and levodopa usually only has a limited effect in improving symptoms.

Neuropsychological testing

It's also likely you'll be referred to a neurologist (a nerve and brain specialist) and you may need to have neuropsychological testing.

This involves having a series of tests to evaluate the full extent of your symptoms and their impact on your mental abilities. The tests will look at abilities such as:

memory
concentration
understanding language
processing visual information, such as words and pictures

Most people with CBD have a distinct pattern in terms of their mental abilities. They often have what's known as subcortical dementia which affects their planning 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 your 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's 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'll need full-time care and you may also need assistant technology, such as a wheelchair, to help with activities.

Read more about practical support and adjusting to a disability.