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What is PCA?

Professor Sebastian Crutch and Dr Tim Shakespeare introduce posterior cortical atrophy.
PCA stands for posterior cortical atrophy, or literally back of the brain shrinkage. And it’s a progressive syndrome where people typically experience visual problems, so gradual loss of the ability to see what and where things are. And it’s not because there’s anything wrong with their eyes, it’s because the visual centres of the brain are slowly degenerating. So they can’t interpret the information coming in from the eyes. So, as I say, the primary problems are usually visual, and experienced often first by difficulties with driving, or reading, visually complex activities. But also other parts of the brain nearby which control function such as reading, writing, arithmetic, and the ability to make skilled and complex movements are often also affected.
There are no good answers to how common posterior cortical atrophy is. There are some estimates, but they’re only estimates for people who have an early onset dementia. So that’s before the age of 65. And posterior cortical atrophy tends to be before the age of 65. It is estimated there are about 65,000 people in the UK with an early onset. And another study has made an estimate of how many people with early onset dementia have PCA, and they reckon about 5%. So, it’s possible about 5% of those 65,000 people have PCA. But those are really just estimates based on studies that kind of aren’t looking to really answer that question. So it’s something that needs to be investigated.


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Professor Sebastian Crutch and Dr Tim Shakespeare introduce posterior cortical atrophy.
  • Posterior cortical atrophy literally means back of the brain shrinkage.
  • The primary symptoms are visual
  • These visual symptoms can cause difficulties initially with complex visual tasks like driving or reading
  • Other skills that rely on the back of the brain such as spelling and calculation may also be affected early
  • PCA tends to be ‘early onset’ (i.e. symptoms starting before age 65)
The number of people with PCA, and even the number of people who have any form of dementia starting before the age of 65 is not well established. The figure of 64,000 with young onset dementia mentioned in this video comes from a report from Alzheimer’s Research UK (formerly the Alzheimer’s Research Trust; DEMENTIA 2010, Table 2). These estimates were created by taking dementia prevalence estimates from a 1991 study including a number of different countries (but with little information on prevalence in the under 65s)1 and applying them to UK population estimates. It’s possible the estimates may not be entirely accurate as they are out of date and data was only available in a small number of the countries that were studied.
Other reports have given an estimate of 42,325 people with early onset dementia in the UK – the Dementia UK Second Edition report from the Alzheimer’s Society used a different approach in which a review of available literature was carried out, and the opinions of a number of experts were collected in a particular way to estimate prevalence. When it comes to estimating the number of people with PCA specifically, not just early onset dementia, the best estimate we have is that 5% of people with Alzheimer’s disease starting before age 65 have a visual presentation2.
As none of these studies directly set out to investigate how many people in the UK have PCA it’s very difficult to make a good estimate. How important do you think it is to have accurate estimates of how many people have dementia, and less common forms of dementia? A detailed study to find out would likely be expensive, would it be worth spending money on this kind of study, or is money better spent on care and research for better diagnosis and treatments?
[1] The Prevalence of Dementia in Europe: A Collaborative Study of 1980-1990 Findings. Hofman et al., International Journal of Epidemiology (1991).
[2] Cognitive phenotypes in Alzheimer’s disease and genetic risk. Snowden et al., Cortex (2007).
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