Neurology

Diagnosing PCA: Scans, Tests, and Biomarkers

At a Glance

Posterior cortical atrophy is diagnosed by combining visual-processing symptoms with specialized cognitive testing, MRI or FDG-PET patterns, and sometimes amyloid, tau, or spinal-fluid biomarkers. No single test confirms PCA, and memory can remain relatively strong early on.

Diagnosing Posterior Cortical Atrophy (PCA) requires a shift in perspective. Because your symptoms are visual, standard dementia screenings that focus heavily on memory may not capture the full extent of your challenges, and you may struggle with them simply because they are visually demanding ^[1]. Instead, doctors use a combination of specialized mental exercises and advanced brain imaging to see how the back of your brain is functioning. No single scan definitively confirms PCA; the diagnosis relies on the clinical picture supported by testing.

Beyond Memory: Neuropsychological Testing

A standard memory test, such as the MMSE or MoCA, might not show much impairment in the early stages of PCA, or testing must be adapted to account for your vision ^[2]. To get an accurate picture, you will likely undergo neuropsychological assessment specifically designed for “higher-order” visual processing ^[3]. These tests look at:

Figure-Ground Discrimination: Your ability to identify a specific shape or object when it is hidden against a busy or cluttered background ^[4].
Visuospatial Construction: Tasks like the Rey-Osterrieth Complex Figure copy, where you are asked to draw a complicated geometric shape ^[5].
Visual Object and Space Perception (VOSP): Specialized subtests like Fragmented Letters (identifying a letter made of broken lines) or Dot Counting ^[3].
Praxis: Testing your ability to perform learned movements, such as mimicking how to use a hammer or a toothbrush, which can be impaired in PCA (a condition called apraxia) ^[4].

Mapping the Brain: MRI and FDG-PET

While eye exams check the health of your eyes, brain scans check the health of your “visual processor.”

Structural MRI: In PCA, an MRI typically shows atrophy (thinning or shrinking) in the back of the brain—the parietal, occipital, and posterior temporal lobes ^[6]. Crucially, the hippocampus (the brain’s primary memory center) may look relatively preserved early on, which is different from what doctors typically see in amnestic Alzheimer’s, though this sparing is not universal ^[7]^[8].
FDG-PET Scan: This scan uses a small amount of radioactive sugar to measure brain activity. In PCA, the scan often shows hypometabolism—areas where the brain is using less energy—in those same posterior regions ^[9]. This pattern of low activity in the back of the brain is a hallmark supportive sign ^[8].

The “Biology” of PCA: Biomarkers

While scans show where the brain is affected, biomarkers show why it is happening. Because Alzheimer’s pathology is the cause in the vast majority of PCA cases, doctors use these tests to investigate the underlying protein buildup ^[10].

Test Type	What it Measures	Why it Matters in PCA
Amyloid PET	Buildup of amyloid plaques.	Confirms the presence of Alzheimer’s biology ^[10].
Tau PET	Buildup of tau “tangles.”	In PCA, tau is heavily concentrated in the back of the brain, matching your visual symptoms ^[11]^[12].
CSF (Spinal Fluid)	Levels of amyloid and tau proteins.	Provides a “biological signature” of Alzheimer’s even if memory is preserved ^[10]^[13].

Differentiating PCA from Other Conditions

The diagnostic process also helps evaluate for look-alike conditions.

Typical Alzheimer’s: Differentiated by early, prominent memory loss and shrinking of the hippocampus on an MRI ^[7].
Dementia with Lewy Bodies (DLB): DLB can also cause visual issues and posterior hypometabolism, but it is diagnosed clinically by visual hallucinations, physical tremors (parkinsonism), REM-sleep behavior disorder, and fluctuations in alertness ^[14]. A specialized scan called a DAT-SPECT (which looks at dopaminergic loss) can provide supportive evidence for DLB, although it is not a definitive rule-out test for PCA ^[15].

By combining these tools, your medical team can move past the “eye problem” confusion and provide a clearer diagnosis of what is happening in your brain ^[16].

Common questions in this guide

Can I have PCA if my memory test is still fairly normal?

Yes. Early PCA often affects visual processing and spatial skills before memory, so standard memory-heavy screenings may miss important difficulties or be hard to complete because of vision problems. Doctors use specialized cognitive tests, brain imaging, and sometimes biomarker testing rather than relying on one memory score.

What does an MRI usually show in posterior cortical atrophy?

An MRI may show shrinkage in the parietal, occipital, and back portions of the temporal lobes. The hippocampus may be relatively preserved early, unlike the more typical memory-loss pattern of Alzheimer's disease, but this finding is not present in every person with PCA. MRI supports the diagnosis but cannot confirm it by itself.

Why might my doctor order an FDG-PET scan for PCA?

An FDG-PET scan measures how actively different brain regions use energy. In PCA, it often shows reduced activity in the back of the brain, where visual processing occurs. This pattern supports PCA and can help clinicians compare it with other conditions, but it is not a definitive test.

What do amyloid and tau tests tell doctors about PCA?

Amyloid and tau PET scans, or a spinal-fluid test, look for the protein changes associated with Alzheimer's disease. These results can show whether Alzheimer's biology may be driving PCA, even when memory is relatively strong. Doctors interpret biomarkers together with symptoms, cognitive testing, and imaging rather than using them alone to diagnose PCA.

How do doctors distinguish PCA from typical Alzheimer's or Lewy body dementia?

Typical Alzheimer's disease more often begins with prominent memory loss and hippocampal shrinkage. Dementia with Lewy bodies is more likely to include visual hallucinations, movement symptoms such as tremor or stiffness, dream-enactment during sleep, and changes in alertness. The overall symptom pattern, cognitive testing, scans, and sometimes a DAT-SPECT scan help clinicians compare these conditions.

Curated prompts to bring to your next appointment.

1.Based on my MRI, is there visible atrophy in my parietal or occipital lobes, and is my hippocampus relatively spared?
2.Which specific neuropsychological tests will be used to measure my visuospatial skills, such as figure-ground discrimination or dot counting?
3.Do you recommend an amyloid or tau PET scan, or a lumbar puncture, to confirm if Alzheimer's pathology is the cause?
4.How do my FDG-PET results help rule out other conditions like Dementia with Lewy Bodies?
5.If my memory is still relatively strong, why does the presence of amyloid or tau proteins mean I have a form of Alzheimer's disease?

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This page explains how posterior cortical atrophy is evaluated for informational purposes only and does not replace professional medical advice. Your neurologist and care team should interpret your scans, cognitive tests, and biomarker results in context.

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