The rare condition posterior cortical atrophy (PCA) involves strange, troubling issues with vision and spatial awareness – including difficulty judging distances, seeing movement, and recognizing objects – and a new study highlights its close relationship to Alzheimer's disease in more detail than ever before.
PCA and Alzheimer's have long been linked with each other, because they share a lot of the same pathological changes in the brain. However, the rarity of PCA has made it hard for researchers to fully assess it in relation to Alzheimer's.
To address that, an international team of researchers analyzed data on 1,092 individuals with PCA, finding that it was a very strong predictor for Alzheimer's: in 94 percent of cases, tell-tale Alzheimer's brain changes were observed, and were most likely contributing to PCA.
"We need more awareness of PCA so that it can be flagged by clinicians," says neuropsychologist Marianne Chapleau from the University of California, San Francisco (UCSF).
"Most patients see their optometrist when they start experiencing visual symptoms and may be referred to an ophthalmologist who may also fail to recognize PCA. We need better tools in clinical settings to identify these patients early on and get them treatment."
One positive effect this study could have is getting people with PCA symptoms checked out as early as possible. The average onset age for the disorder is 59 – several years younger than it is for Alzheimer's – and the average time between symptom onset and the first diagnostic visit is 3.8 years.
The study noted plenty of similarities between PCA and Alzheimer's in terms of the levels of amyloid and tau in the brain, with build-ups of these proteins long associated with the onset of dementia.
However, there were also some differences, which could give researchers clues as to the best courses of treatment.
"Patients with PCA have more tau pathology in the posterior parts of the brain, involved in the processing of visuospatial information, compared to those with other presentations of Alzheimer's," says neuropsychologist Renaud La Joie from UCSF. "This might make them better suited to anti-tau therapies."
The researchers behind the new study are hopeful that their work can lead to a greater understanding of how Alzheimer's can manifest itself, and how both Alzheimer's and PCA start to get a grip on the brain.
With this research covering people in 16 different countries, it's the most comprehensive review of PCA yet – and because of its close links to Alzheimer's, it gives us a different perspective on dementia than we otherwise get.
"From a scientific point of view, we really need to understand why Alzheimer's is specifically targeting visual rather than memory areas of the brain," says neurologist Gil Rabinovici from UCSF.
"Our study found that 60 percent of patients with PCA were women – better understanding of why they appear to be more susceptible is one important area of future research."
The research has been published in Lancet Neurology.