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Posterior cortical atrophy (PCA) is a type of young-onset dementia affecting vision that is caused not by problems with the eyes, but by damage to the back of the brain.

Eye test equipment

‘Posterior’ means back, ‘cortical’ means outer layer of the brain, and ‘atrophy’ means shrunken body part. Put together to give PCA, they mean the back, outer part of the brain has decreased in size. This shrinkage is the result of damage to brain cells, which can be caused by things like Alzheimer’s disease, Lewy bodies (small, obstructive proteins) or prion disease (tiny, aggressive proteins).

The back of the brain is in charge of vision and sensory processing. So, people with PCA have difficulty processing visual information, making tasks that rely on vision, like reading, very difficult. The symptoms each person with PCA experiences will differ depending on the exact pattern of damage to their brain.

Problems with vision that someone with PCA may experience include distortions, sensitivity to light, seeing unusual colours, and visual hallucinations. Some other symptoms could be difficulty spelling, identifying objects, recognising faces, and understanding numbers. People with PCA may also have trouble moving around in their surroundings due to disorientation, and experience challenges with coordination and manoeuvring.

Even though Alzheimer’s disease can be a cause of PCA, memory problems are not a symptom until the later stages of the condition – whereas memory loss is one of the first symptoms affecting people with typical Alzheimer’s disease.

PCA most commonly occurs at age 50-65, but there is often a long delay in reaching a diagnosis. This is because diagnosis usually starts with an eye test that shows no issue with the person’s eyes. If the eye specialist is aware of PCA, they may then refer the patient to a neurologist, a specialist brain doctor. However, if they are not experienced with PCA, the person may be misdiagnosed, or not receive their diagnosis until their symptoms are considerably worse.

These diagnosis issues are because PCA is so rare – estimates suggest that only 5% of people with Alzheimer’s have PCA, which itself is just one of many types of dementia. It could also be because the age PCA presents itself is young compared with most other dementias. There are also no standard criteria for diagnosis yet, meaning doctors must rule out other potential reasons for the symptoms before reaching a diagnosis of PCA – this uses up precious time.

A team at University College London has been running a long-term study of PCA since 2005 to improve characterisation and diagnosis of PCA. Through yearly assessments of their participants, including thinking tests and brain scans, the study aims to understand more about PCA and how symptoms could be treated.

Currently, we do not know why people develop PCA or what risk factors there are for it. There is also no medication that specifically treats PCA, although some people find that drugs designed for Alzheimer’s disease or Parkinson’s help their symptoms.

The charity Rare Dementia Support recommends people with PCA try visual aids like sensors that inform the user when a cup is full, talking clocks, and technology with big buttons and a simple display. Controlling light levels by switching lights on before it gets dark and using lampshades to soften harsh lights can also help people with PCA to understand their surroundings better. Rare Dementia Support also provides support for people diagnosed with PCA through support groups and thorough advice.

The late author Terry Pratchett, who lived with PCA for seven years, said: ‘It is a physical disease, not a mystic curse; therefore it will fall to a physical cure.’ You can read his full account of his experience with PCA here.