Posterior cortical atrophy: symptoms and diagnosis

The name describes what happens. "Posterior" means the back of the brain, "cortical" refers to the outer layer where thinking and perception are processed, and "atrophy" means shrinkage through loss of brain cells. The regions most affected are the occipital and parietal lobes, which turn the signals sent by the eyes into a meaningful picture of objects and space.

PCA is best understood as a syndrome, a recognisable pattern of symptoms, rather than a single disease. The Alzheimer's Society places it among the "atypical" forms of Alzheimer's disease, which account for around 1 in 20 people with Alzheimer's who have different early symptoms from the usual memory problems.

Very little is known about why PCA affects some people and not others, and nobody can say with confidence how many people live with it. Ongoing research at the Dementia Research Centre in London is trying to improve that picture.

The first signs are often subtle and hard to put into words. Someone may find that lines of text seem to jumble, that a familiar face is not recognised until the person speaks, or that the stairs look flat. The brain is receiving the image correctly from the eyes but cannot interpret it.

Rare Dementia Support lists common early difficulties, and notes that language, spelling and arithmetic can sometimes be the first thing noticed instead.

• Trouble reading, such as losing the place in a line or words appearing to move together.

• Difficulty recognising objects and people, including faces on television.

• Poor judgement of distance and speed, for example when driving, crossing a road or stepping onto an escalator.

• Clumsiness with everyday tasks such as picking up objects, getting dressed or pressing the right telephone keys.

• Sensitivity to light and unusual colour effects, such as washes of colour when driving at night.

• Problems with spelling, handwriting, remembering the shape of letters or numbers, and mental arithmetic.

In the middle stages, people often still understand what everyday activities are for, but they need more help doing them as vision and spatial skills decline. Cooking, reading labels, handling money, telling the time and finding the way around a familiar house can all become hard. Many people keep considerable awareness of their situation, which can make the experience frustrating.

Later, vision can become severely affected. The world may look like pieces of a puzzle, with small details noticed but their relationship to each other lost. Walking safely can need supervision because the edges of pavements and steps are hard to detect. Rare Dementia Support says that at this stage many people are registered as blind.

Other senses can be involved too, including sensitivity to pain or temperature, changes in hearing, a feeling of imbalance and small jerky movements. Everyone's course is different, and people do not necessarily pass through any fixed order of stages.

In the large majority of cases the brain changes are those of Alzheimer's disease. The difference from typical Alzheimer's is where they begin: memory regions are particularly affected in the usual form, whereas in early PCA it is the skills controlled by the rear of the brain, such as vision, that suffer first.

A small number of other conditions can produce the same pattern. Rare Dementia Support names Lewy body disease, where visual hallucinations and slowed, stiffer movements may appear; corticobasal syndrome, which can cause difficulty using one side of the body; and very rarely prion diseases, which tend to progress quickly. Working out which underlying disease is responsible matters because it affects which treatments are likely to help.

Nothing a person did is known to cause PCA, and it is not currently possible to prevent it.

Most people first see an optician because sight seems to be the problem. An optician will usually find healthy eyes, which can lead to a long search. A GP who hears that someone has normal eye tests but real difficulty seeing, reading or judging space can consider referral to a specialist, usually a neurologist, psychiatrist or neuro-ophthalmologist.

There is no single test for PCA. Rare Dementia Support lists several investigations that together help build the picture and rule out treatable causes such as infection, inflammation or a tumour.

• Specialised visual tests arranged by eye specialists.

• Pen-and-paper and computer tests of thinking skills, including visual perception, literacy and memory.

• Blood tests.

• Brain scans, MRI or CT, which may show shrinkage at the back of the brain.

• In some people a lumbar puncture or an electroencephalogram (EEG).

The Alzheimer's Society states that there are no specific drugs to treat PCA. Some thinking and memory symptoms may improve slightly with donepezil, rivastigmine or galantamine, the medicines used for Alzheimer's disease. Rare Dementia Support stresses that these manage symptoms and are not a cure, and that anyone considering them should talk to their GP or specialist first.

Low mood and depression are common reactions and are treatable, with antidepressants or talking therapies. People with movement stiffness may be offered treatments used in parkinsonism. Occupational therapists, sight-loss services, social workers and community mental health teams can all contribute, even though PCA is rare enough that some local services have little direct experience of it.

Practical adaptations vary from person to person: clear contrast on stairs, uncluttered surfaces, large-print or audio material and help with driving decisions are examples people commonly discuss.

Receiving the diagnosis can be isolating for the person and for those close to them. Rare Dementia Support runs support groups for people with PCA, carers, family and friends, including a London group, smaller groups and regional hubs. Talking with others who have met the same problems can be a useful source of practical advice.

Many people with PCA retain insight and a strong sense of who they are, so planning ahead early can be empowering. Topics usually worth raising include driving, legal and financial arrangements, how and when to tell friends and colleagues, and what support might be needed at home. Some people also choose to take part in research, which is open to those with a diagnosis.

PCA itself does not usually cause an emergency, but sudden new symptoms need different thinking. A sudden loss of vision, a drooping face, new weakness or slurred speech should be treated as a possible stroke and 999 should be called. New confusion over hours or days, particularly with a fever or after a fall, should be assessed urgently, for example through NHS 111.

For slowly worsening problems with vision, reading or spatial tasks that an eye test does not explain, the usual first step is a GP appointment, then referral to a memory service, neurology or neuro-ophthalmology on the NHS. People who see a specialist privately can ask for the same range of assessments and should share the results with their GP so that care stays joined up. Facilities and services differ between providers, so it helps to check what a service offers before attending.