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What is PCA?

Professor Sebastian Crutch and Dr Tim Shakespeare introduce PCA, and why it's so difficult to know how many people in the UK have it.

What is PCA?

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

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It’s possible the estimates may not be entirely accurate as they are out of date and data was only available in a small number of the countries that were studied.

The Dementia UK Second Edition

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.

Why it is so difficult to know how many people have PCA

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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