We often talk more about the common forms of dementia, such as Alzheimer’s disease and Vascular dementia, which, together, account for ~70-80% of all people with dementia. The remaining ~20-30% of dementia get often overlooked and are therefore also commonly under-recognised or plainly misunderstood.
Time to change that.
In this series, we are going to explore some of those ‘rarer’ forms of dementia. First off, a rare form of Alzheimer’s disease – Posterior Cortical Atrophy.
What is Posterior Cortical Atrophy?
It may come as a surprise that Posterior Cortical Atrophy is a rare form of Alzheimer’s disease, as it does not even have ‘Alzheimer’s disease’ in its name. The reason for this is that for many decades Posterior Cortical Atrophy was not even recognised by the scientific and clinical world as a form of Alzheimer’s disease. It took until the 1990s until a consensus was reached that people with the symptoms of Posterior Cortical Atrophy have, in fact, Alzheimer’s disease.
What are the symptoms in Posterior Cortical Atrophy?
When we think of Alzheimer’s disease we mostly think of memory symptoms, such as forgetting recent events or becoming disorientated. However, people with Posterior Cortical Atrophy rarely have such memory problems at the beginning of the disease. Instead, they report problems with their vision, which we commonly do not associate with Alzheimer’s disease. Since these visual symptoms are unusual for the more common form of Alzheimer’s disease, they are also much harder to spot and verify. Indeed, most people with Posterior Cortical Atrophy report as first symptoms to ‘bump into furniture’, misjudging distances or having problems seeing parts of their visual field. Having such symptoms leads most people in the first instance to a visit to their optometrist or an opthalmologist to get their eyes checked. Maybe their eyesight got worse or they have developed a cataract (a common condition in ageing when part of the lens of the eye becomes cloudy restricting the vision) or glaucoma (when the nerve connecting the eye and the brain becomes damaged due to too much pressure in the eye)? All very reasonable explanation of why our vision might have changed when we age. But often the optometrist or ophthalmologist does not find any significant problems in their eyes and even if new glasses are prescribed or they undergo a cataract operation, the symptoms persist. This tells us that the visual problems in Posterior Cortical Atrophy are not caused by the eyes but the brain.
The name Posterior Cortical Atrophy already gives a hint that this a brain disease and not an eye disease, since ‘posterior cortical’ refers to the superficial areas at the back of the brain (Atrophy means ‘shrinkage’ of brain tissue because of the dementia disease process). The name tells us, therefore, that the changes in this disease are caused at the back of the brain. It is at the back of our brain where also our main vision areas are located. This comes often as a surprise to people who would expect that our visual brain areas must be close to our eyes, at the front of the brain, but it is exactly the opposite, the brain areas for vision are at the back of our brain. Blame our brain evolution for this strange arrangement.
The key to understanding the visual symptoms in Posterior Cortical Atrophy is to know how our vision brain areas work and ‘re-assemble’ the information they receive from our eyes. It might sound strange that the brain ‘re-assembles’ the visual information from our eyes, as one would assume that the brain simply is a mirror of what we see. But that is not correct. The visual information from the eyes arriving at the brain areas has to be ‘re-assembled’ so that we can actually see what our eyes see. It is somewhat comparable to our TV working, which is send data packages via our antenna or our internet router and then ‘re-assembles’ this information to show us the data packages as moving pictures on the screen. The process is very similar to the brain, where the eyes are similar to an antenna receiving the visual information and the visual areas in the brain to our TV which ‘re-assembles’ the visual information from our eyes.
Two brain structures are critical for the ‘re-assembling’ of our visual information, the occipital cortex and the parietal cortex, which lie both at the back of the brain. The occipital cortex is also referred to as the primary visual cortex, as it receives the raw data/input from our eyes. The occipital cortex starts to reassemble this information into simple shapes and patterns, which are then forwarded to other brain regions, for further processing. The parietal cortex is one of those regions receiving a lot of visual input from the occipital cortex. Conveniently, the parietal cortex lies next to and above to the occipital cortex, showing the strong relationship the two have with each other. However, the parietal cortex is not only processing visual information but many other information inputs from our senses, such as touch and hearing. The parietal cortex is therefore a more complex ‘beast’ as it integrates many different sensory components.
What has this all to do with Posterior Cortical Atrophy?
In Posterior Cortical Atrophy, the disease-specific changes for Alzheimer’s disease, namely the accumulation of two proteins (amyloid and tau) causes the nerve cells in the parietal and occipital cortex to be damaged. This damage of nerve cells in the parietal and occipital cortex causes, therefore, the reassembly of the visual information in the brain to be disrupted. People with Posterior Cortical Atrophy often report therefore having a blind spot, a part of their visual field where they just have a black spot and cannot see, others have problems seeing parts of their visual field, such as not being able to see things on your right or left side of your visual field. As we already know these changes are not caused by changes to the eyes, which are working perfectly well but instead are the damaged nerve cells in the parietal and occipital cortex which are causing the symptoms. Getting a new pair of glasses or having an assessment for a cataract or glaucoma will not help in these circumstances as the eyes are working perfectly fine.
However, since Posterior Cortical Atrophy is much rarer than the ‘classic’ form of Alzheimer’s disease, it is often later recognised, even by specialists. Instead, people getting often referred between optometrists, eye doctors, GPs and neurologists, until someone spots the actual cause of the visual changes in the person. Another key aspect of Posterior Cortical Atrophy is that it occurs often in younger people and is therefore referred to as Young-Onset Dementia. Young-Onset Dementias are types of dementia which occur more commonly before the age of 65, whereas Alzheimer’s disease and Vascular Dementia are often referred to as Later Onset Dementia. Having dementia before you are 65 is another unusual aspect of Posterior Cortical Atrophy and again causes people to get a later diagnosis, as family doctors would not assume for someone to have dementia in their 50s or 60s but that is exactly the case for Posterior Cortical Atrophy. I would recommend to anyone with Posterior Cortical Atrophy to seek out specific Young-Onset Dementia support groups, as they will provide more tailored support to their age group and symptoms.
It is important for us all to know that Alzheimer’s disease can not only cause memory problems but in rarer cases visual problems in younger people (before the age of 65). Posterior Cortical Atrophy should be, therefore, considered to be a ‘visual form’ of Alzheimer’s disease, which, in my opinion, would be a much better and less confusing label. This will also inform better care for those visual symptoms. People with Posterior Cortical Atrophy are clearly less interested in care targeting memory problems since they do not have any, but it is far more important for them and their carers to know how to deal with the visual problems. In particular, visual problems can have a major impact on the confidence of the people with Posterior Cortical Atrophy, as changes to our vision make us much more hesitant and less confident to move around or go outside. In turn, this might impact our independence, since our hesitation and loss of confidence will lead us to do fewer things by ourselves, including any outdoor activities.
But it’s not all bad news.
There has been over the recent years an effort been made to educate optometrists and ophthalmologists of Posterior Cortical Atrophy so that people with this rarer form of Alzheimer’s disease can be spotted and diagnosed earlier. The reason is to diagnose them earlier is that since Posterior Cortical Atrophy has underlying Alzheimer’s disease brain changes, the upcoming Alzheimer’s disease medication can be potentially used in Posterior Cortical Atrophy, as well to slow down the disease process. However, we need to make clear that this is at the moment a theoretical assumption, which needs to be confirmed by future clinical trials in Posterior Cortical Atrophy. Still, earlier detection of Posterior Cortical Atrophy would clearly help many people not only in receiving an earlier diagnosis but also better disease management – including saving us the money for new glasses.
Now, there is a vision!