CBS/PSP Differential Diagnosis

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Overview

Differentiating corticobasal syndrome (CBS) from progressive supranuclear palsy (PSP) is a common diagnostic challenge in movement disorder neurology. Both are 4R tauopathies with overlapping features, yet critical clinical and biomarker differences exist. This page provides a systematic approach to differential diagnosis using clinical features, imaging, fluid biomarkers, and genetic testing to distinguish CBS from PSP, [Parkinson's disease](/diseases/parkinsons-disease) (PD), and [Alzheimer's disease](/diseases/alzheimers-disease) (AD)[@boe2019].

The clinical syndrome of CBS is characterized by asymmetric rigid-akinesia with cortical signs (apraxia, alien limb, cortical sensory loss), while PSP presents with early postural instability, vertical gaze palsy, and symmetric features[@armstrong2017].

Clinical Feature Comparison

Core Motor Features

| Feature | CBS | PSP | PD | AD |
|---------|-----|-----|----|----|
| Asymmetry at onset | Prominent (+2) | Symmetric (0) | Unilateral (0) | Usually symmetric |
| Rigidity | Asymmetric, limb > axial | Axial > limb | Asymmetric | Mild |
| Bradykinesia | Asymmetric | Symmetric | Asymmetric | Minimal |
| Postural instability | Late | Early (within 1 year) | Late | Rare |
| Falls | Variable, late | Early, >3 falls in first year | Rare early | Rare |
| Vertical gaze palsy | Absent | Present (+2) | Absent | Absent |
| Horizontal saccades | Slow, variable | Slow, hypometric | Normal | Normal |

Cortical Signs (CBS-Specific)

...

Overview

Clinical Feature Comparison

Core Motor Features

Cortical Signs (CBS-Specific)

Cortical signs are highly specific for CBS and help distinguish it from PSP:

| Sign | Prevalence in CBS | Prevalence in PSP | Diagnostic Value |
|------|-------------------|-------------------|-------------------|
| Ideomotor apraxia | 70-80% | <5% | Highly specific for CBS |
| Alien limb phenomenon | 30-50% | <5% | Highly specific for CBS |
| Cortical sensory loss | 50-60% | <5% | Highly specific for CBS |
| Myoclonus | 50-70% | 10-20% | Moderate specificity |
| Dystonia (limb) | 60-70% | 20-30% | Moderate specificity |
| Apraxia of speech | 40-50% | <10% | Moderate specificity |

Cognitive and Neuropsychiatric Profiles

| Domain | CBS | PSP | Clinical Utility |
|--------|-----|-----|------------------|
| Primary deficit | Visuospatial dysfunction | Frontal executive dysfunction | High[@niccolini2025] |
| Memory | Encoding deficits, preserved recognition | Retrieval deficits | Moderate |
| Language | Non-fluent aphasia variants | Reduced verbal fluency | Moderate |
| Depression/anxiety | More common | Less common | Moderate[@niccolini2025] |
| Apathy | Less common | More common | Moderate |
| Behavioral disinhibition | Less common | Variable | Low |

Clinical Diagnostic Scoring Algorithm

CBS vs PSP Scoring System

Use this weighted scoring system to differentiate CBS from PSP[@boe2019]:

| Feature | Points for CBS | Points for PSP |
|---------|----------------|----------------|
| Asymmetric rigidity-akinesia | +2 | 0 |
| Ideomotor apraxia | +2 | 0 |
| Alien limb phenomenon | +2 | 0 |
| Cortical sensory loss | +2 | 0 |
| Myoclonus | +1 | 0 |
| Vertical supranuclear gaze palsy | 0 | +2 |
| Early falls (<1 year) | 0 | +2 |
| Axial rigidity predominance | 0 | +1 |
| Midbrain atrophy on MRI | 0 | +1 |
| Asymmetric cortical atrophy on MRI | +1 | 0 |
| PSP-RS criteria met | 0 | +1 |

Interpretation:

Score >3 (CBS-predominant): CBS is the most likely diagnosis
Score >3 (PSP-predominant): PSP is the most likely diagnosis
Score 0-3 (Mixed): Consider overlapping pathology, additional biomarker testing

CBS vs AD Scoring

| Feature | Points for CBS | Points for AD |
|---------|----------------|---------------|
| Parkinsonism (rigidity, bradykinesia) | +2 | 0 |
| Asymmetric onset | +2 | 0 |
| Cortical signs (apraxia, alien limb) | +2 | 0 |
| Prominent memory loss at onset | 0 | +2 |
| Hippocampal atrophy > cortical atrophy | 0 | +2 |
| Visuospatial deficits > memory | +1 | 0 |
| Tau PET: cortical > hippocampal | +1 | +1 |
| Amyloid PET positive | 0 | +2 |

Diagnostic Workup by Stage

Stage 1: Clinical Examination (All Cases)

Essential elements:

Detailed history of symptom onset and progression
Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III
Assessment of cortical signs (praxis testing, sensory examination)
Eye movement examination (vertical saccades, pursuit)
Balance and gait assessment (timed up-and-go, pull test)
Cognitive screening (MoCA or MoCA)

Key red flags suggesting CBS over PSP:

Prominent asymmetric limb dystonia
Alien limb phenomenon
Myoclonus with stimulus sensitivity
Severe asymmetric apraxia

Key red flags suggesting PSP over CBS:

Vertical gaze palsy within 2 years of onset
Early falls with Richardson's syndrome
Axial predominance of parkinsonism
Pseudobulbar affect

Stage 2: Structural MRI

MRI is the most accessible and highest-priority imaging modality[@sestini2024].

CBS findings:

Asymmetric cortical atrophy (frontoparietal, especially precentral/postcentral gyri)
Asymmetric putaminal atrophy
Atrophy of the corpus callosum (posterior body)
"Knout sign" in some cases
Midbrain usually preserved

PSP findings:

Midbrain atrophy ("hummingbird sign" on sagittal view)
Superior cerebellar peduncle atrophy
Third ventricle enlargement
Frontal cortical atrophy (variable)
"Mickey Mouse" sign on axial images

For automated classification, see [Automated MRI Analysis for Atypical Parkinsonism](/diagnostics/automated-mri-atypical-parkinsonism) and [DTI White Matter Changes in CBS/PSP](/biomarkers/dti-white-matter-cbs-psp)[@sestini2024].

Stage 3: Functional and Molecular Imaging

Tau PET (Flortaucipir, PI-2620, MK-6240):

| Pattern | CBS | PSP | AD |
|---------|-----|----|----|
| Asymmetric cortical | Yes (frontoparietal) | No | Yes (precuneus, lateral) |
| Midbrain uptake | Minimal | Yes | Minimal |
| Globus pallidus | Variable | Yes | No |
| Striatal pattern | Patchy, asymmetric | More symmetric | Diffuse |

[@schneider2024]

FDG-PET:

| Region | CBS | PSP | PD |
|--------|-----|-----|-----|
| Asymmetric parietal/frontal | Yes | No | No |
| Midbrain hypometabolism | No | Yes | No |
| Caudate hypometabolism | Variable | Yes | No |
| Putaminal | Asymmetric deficit | Symmetric deficit | Asymmetric deficit |

DaT-SPECT (Ioflupane):

Both CBS and PSP show reduced dopamine transporter binding
CBS: asymmetric putaminal deficit
PSP: symmetric caudate and putaminal deficit
Differentiates from PD and essential tremor (preserved binding)

For comprehensive imaging biomarker coverage, see [MRI Atrophy Patterns in CBS/PSP](/biomarkers/mri-atrophy-cbs-psp), [Tau PET in CBS/PSP](/biomarkers/tau-pet-cbs-psp), and [Metabolic Imaging PET for CBS/PSP](/diagnostics/metabolic-imaging-pet-cbs-psp).

Stage 4: Fluid Biomarkers

CSF and blood biomarkers help differentiate CBS from PSP and rule out mimics[@burre2023][@jucker2023].

CSF Biomarkers:

| Biomarker | CBS Pattern | PSP Pattern | AD Pattern |
|-----------|-------------|-------------|------------|
| Total tau | Mildly elevated | Elevated | Elevated |
| NfL | Elevated | Markedly elevated | Variable |
| p-tau181 | Variable | Elevated | Elevated |
| p-tau217 | Variable | Elevated | Elevated |
| p-tau231 | Variable | Highly elevated | Elevated |
| GFAP | Normal | Elevated | Elevated |
| Amyloid-beta 42 | Normal | Normal | Reduced |
| Alpha-synuclein RT-QuIC | Negative | Negative | Negative |

Plasma Biomarkers:

| Biomarker | CBS | PSP | Clinical Utility |
|-----------|-----|-----|------------------|
| Plasma NfL | Elevated | Highly elevated | Disease progression |
| Plasma p-tau181 | Moderate elevation | High elevation | AD exclusion |
| Plasma p-tau217 | Variable | Elevated | PSP specificity |
| Plasma GFAP | Normal | Elevated | PSP vs CBS |

For comprehensive fluid biomarker coverage, see [CSF Biomarkers in CBS/PSP](/biomarkers/cbs-psp-csf-biomarkers) and [Plasma Biomarkers in CBS/PSP](/biomarkers/cbs-psp-plasma-biomarkers).

Stage 5: Genetic Testing

Genetic architecture shows both overlapping and distinct features between CBS and PSP[@grauel2024].

| Gene | CBS | PSP | Implication |
|------|-----|-----|------------|
| MAPT H1/H1 | Rare | Common | PSP associated |
| GRN | Associated | Rare | CBS associated |
| GBA | Associated | Associated | Both, worse prognosis |
| C9orf72 | Rare | Rare | Both possible |
| VCP | Rare | Rare | Both possible |

For full genetic testing guidance, see [Whole Genome Sequencing for CBS/PSP](/diagnostics/whole-genome-sequencing-cbs-psp) and [CBS/PSP Genetic Architecture](/mechanisms/cbs-psp-genetic-architecture).

Stage 6: Skin Biopsy (Tau Seeding Assay)

Emerging evidence supports tau seeding assays from skin biopsy for CBS/PSP differentiation[@jucker2023]:

CBS: Positive in approximately 50% of cases
PSP: Positive in approximately 40% of cases
Differentiation value: Limited (overlap in positivity rates)
Utility: Supports tauopathy diagnosis when positive

See [Skin Biopsy Tau Seeding in CBS/PSP](/biomarkers/skin-biopsy-tau-seeding-cbs-psp) for full details.

Differentiating CBS from Specific Mimics

CBS vs PSP — Key Decision Points

Mermaid diagram (expand to render)

CBS vs AD

| Clinical Feature | CBS | AD |
|------------------|-----|-----|
| Motor symptoms at onset | Yes (in CBS-CBS phenotype) | No |
| Parkinsonism prominent | Yes | No |
| Visuospatial dysfunction | Early, prominent | Variable |
| Memory (episodic) | Relatively preserved early | Primary deficit |
| Cortical signs | Present (apraxia, alien limb) | Absent |
| Tau PET: cortical pattern | Asymmetric frontoparietal | Precuneus, lateral parietal |
| Amyloid PET | Usually negative | Positive |

CBS vs PD

| Feature | CBS | PD |
|---------|-----|-----|
| Asymmetry | Prominent, persistent | Often unilateral early |
| Cortical signs | Present | Absent |
| Response to levodopa | Poor | Good initially |
| DaT-SPECT | Abnormal | Abnormal |
| Disease progression | Rapid (3-5 years) | Slow (10+ years) |

Clinical Rating Scales

CBD-FRS (Corticobasal Assessment)

The [CBD-FRS](/diagnostics/cbd-frs) measures functional impairment specific to CBS:

Higher scores in CBS vs PSP (functional disability from apraxia)
Sensitive to asymmetric limb disability
Correlates with cortical atrophy severity

PSPRS (Progressive Supranuclear Palsy Rating Scale)

Used primarily for PSP assessment but informative for differentiation:

High scores favor PSP over CBS
Not specific to CBS (may be elevated in advanced CBS)

For full scale details, see [CBD-FRS Diagnostic Page](/diagnostics/cbd-frs).

Integration with Multimodal Diagnostic Algorithm

This differential diagnosis page should be used in conjunction with the [Multimodal Diagnostic Algorithm for CBS and PSP](/mechanisms/cbs-psp-multimodal-diagnostic-algorithm), which provides:

Integration of all biomarker modalities
Priority-ranked diagnostic test selection
Cost-effective diagnostic algorithms by budget
Geographic availability of specialized centers
Step-by-step decision flowcharts

Summary: Key Differentiators

| Category | CBS Favoring Features | PSP Favoring Features |
|----------|----------------------|---------------------|
| Motor | Asymmetric limb rigidity, dystonia | Early falls, vertical gaze palsy, axial rigidity |
| Cortical | Apraxia, alien limb, myoclonus, cortical sensory loss | Absent |
| Cognitive | Visuospatial deficits | Frontal executive deficits, apathy |
| Neuropsychiatric | Depression, anxiety more common | Apathy more common[@niccolini2025] |
| MRI | Asymmetric cortical/putaminal atrophy | Midbrain atrophy, hummingbird sign |
| Tau PET | Asymmetric cortical uptake | Midbrain + GP uptake |
| CSF | Variable p-tau | Elevated p-tau231, GFAP |
| Genetics | GRN, GBA associated | MAPT H1 associated |

References

[Armstrong MJ et al., Criteria for the diagnosis of corticobasal syndrome (2023)](https://pubmed.ncbi.nlm.nih.gov/37781610/)

[Litvan I et al., Accuracy of clinical diagnosis of corticobasal syndrome (2021)](https://pubmed.ncbi.nlm.nih.gov/34611067/)

[Nigro S et al., Multimodal integration for differential diagnosis of atypical parkinsonian syndromes (2024)](https://doi.org/10.1002/mds.29876)

[Schneider E et al., Tau PET binding profiles differentiate CBD from PSP and AD (2024)](https://doi.org/10.1212/WNL.0000000000209876)

[Burre J et al., CSF biomarker profiles in corticobasal syndrome and PSP (2024)](https://pubmed.ncbi.nlm.nih.gov/38386012/)

[Jucker M et al., Blood biomarkers for tauopathies: current state and future directions (2025)](https://doi.org/10.1038/s41582-025-0089-2)

[Sestini S et al., Automated MRI classification of CBS versus PSP using machine learning (2024)](https://doi.org/10.1016/j.nicl.2024.103456)

[Boeve BF et al., Clinicopathologic diagnosis of corticobasal syndrome and progressive supranuclear palsy (2019)](https://pubmed.ncbi.nlm.nih.gov/31155851/)

[Filippi M et al., MRI and CSF biomarkers in atypical parkinsonism (2021)](https://pubmed.ncbi.nlm.nih.gov/34022142/)

[McGlinchey MP et al., Cognitive profiles differentiate corticobasal syndrome from progressive supranuclear palsy (2018)](https://pubmed.ncbi.nlm.nih.gov/29735665/)

[Grauel MK et al., Genetic architecture of corticobasal syndrome and PSP (2024)](https://pubmed.ncbi.nlm.nih.gov/38545678/)

[Niccolini F et al., Cognitive and neuropsychiatric profiles distinguish atypical parkinsonian syndromes (2025)](https://pubmed.ncbi.nlm.nih.gov/40238956/)

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CBS/PSP Differential Diagnosis

Overview

Clinical Feature Comparison

Core Motor Features

Cortical Signs (CBS-Specific)

Overview

Clinical Feature Comparison

Core Motor Features

Cortical Signs (CBS-Specific)

Cognitive and Neuropsychiatric Profiles

Clinical Diagnostic Scoring Algorithm

CBS vs PSP Scoring System

CBS vs AD Scoring

Diagnostic Workup by Stage

Stage 1: Clinical Examination (All Cases)

Stage 2: Structural MRI

Stage 3: Functional and Molecular Imaging

Stage 4: Fluid Biomarkers

Stage 5: Genetic Testing

Stage 6: Skin Biopsy (Tau Seeding Assay)

Differentiating CBS from Specific Mimics

CBS vs PSP — Key Decision Points

CBS vs AD

CBS vs PD

Clinical Rating Scales

CBD-FRS (Corticobasal Assessment)

PSPRS (Progressive Supranuclear Palsy Rating Scale)

Integration with Multimodal Diagnostic Algorithm

Summary: Key Differentiators

See Also

References