|Posterior Cortical Atrophy |
A topic in the Alzheimer’s Association series on understanding dementia.
Dementia is a condition in which a person has significant difficulty with daily functioning because of problems with thinking and memory. Dementia is not a single disease. It’s an overall term — like “heart disease” — that covers a wide range of specific medical conditions, including Alzheimer’s disease. Disorders grouped under the general term “dementia” are caused by abnormal brain changes. These changes trigger a decline in thinking skills, also known as cognitive abilities, severe enough to impair daily life and independent function. They also affect behavior, feelings and relationships.
Brain changes that cause dementia may be temporary, but they are most often permanent and worsen over time, leading to increasing disability and a shortened lifespan. Survival can vary widely, depending on such factors as the cause of the dementia, age at diagnosis and coexisting health conditions, as well as other currently unknown factors.
Posterior cortical atrophy (PCA) refers to gradual and progressive degeneration of the outer layer of the brain (the cortex) in the part of the brain located in the back of the head (posterior). It is not known whether PCA is a unique disease or a possible variant form of Alzheimer’s disease. In many people with PCA, the affected part of the brain shows amyloid plaques and neurofibrillary tangles, similar to the changes that occur in Alzheimer’s disease but in a different part of the brain. In other people with PCA, however, the brain changes resemble other diseases such as Lewy body dementia or a form of Creutzfeld-Jacob disease. Most cases of Alzheimer’s disease occur in people age 65 or older, whereas the onset of PCA commonly occurs between ages 50 and 65.
There is no standard definition of PCA and no established diagnostic criteria, so it is not possible to know how many people have the condition. Some studies have found that about 5 percent of people diagnosed with Alzheimer’s disease have PCA. However, because PCA often goes unrecognized, the true percentage may be as high as 15 percent. Researchers and physicians are working to establish a standard definition and diagnostic criteria for PCA.
The symptoms of PCA can vary from one person to the next and can change as the condition progresses. The most common symptoms are consistent with damage to the posterior cortex of the brain, an area responsible for processing visual information. Consistent with this neurological damage are slowly developing difficulties with visual tasks such as reading a line of text, judging distances, distinguishing between moving objects and stationary objects, inability to perceive more than one object at a time, disorientation, and difficulty maneuvering, identifying, and using tools or common objects. Some patients experience hallucinations. Other symptoms can include difficulty performing mathematical calculations or spelling, and many people with PCA experience anxiety, possibly because they know something is wrong. In the early stages of PCA, most people do not have markedly reduced memory, but memory can be affected in later stages.
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Misdiagnosis of PCA is common, owing to its relative rarity and unusual and variable presentation. Additionally, people with PCA frequently first seek the opinion of an ophthalmologist who may indicate a normal eye examination by their usual tests. Because the first problems are perceived as eye problems, cortical brain dysfunction initially may not be considered as a cause.
There are no standard diagnostic criteria for PCA, although diagnostic criteria are being developed. Physicians rely on a combination of neuropsychological tests, blood tests, brain scans and a neurological examination to diagnose the condition and rule out other potential explanations for symptoms. Characteristic features that are sometimes used for diagnosis include gradual onset of visual symptoms (described above) with preservation of normal eye function and preservation of memory. Age of onset between 50 and 65 years is another clue suggesting PCA. The diagnosis should rule out the possibility that the symptoms were caused by a stroke, tumor or other identifiable condition.
There is an ongoing discussion in the field whether PCA should be considered a form of Alzheimer’s disease or a distinct disease entity. Brain imaging has shown that the posterior cortex is thinner in people with PCA than healthy people of the same age. This indicates that the individual has experienced a decrease in brain volume. Furthermore, people with PCA have degeneration in different parts of the brain than people with typical forms of Alzheimer’s disease, although there is often overlap between the two conditions.
Similar to Alzheimer’s disease, the causes of PCA are unknown, and no obvious genetic mutations have been shown to be linked to the condition. It is also not known if the risk factors for Alzheimer’s disease are also risk factors for PCA.
There are no treatments for PCA known to slow or halt its progression. Because PCA resembles Alzheimer’s disease in some patients, it has been suggested that drugs used to temporarily alleviate brain dysfunction in Alzheimer’s disease may be helpful in PCA, but this is not proven. Some people with PCA may benefit from treatment to alleviate symptoms such as depression or anxiety, but the overall benefits and risks of such treatments are not established.