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 (PD), and Alzheimer's 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[1].
| 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 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 |
| Domain | CBS | PSP | Clinical Utility |
|---|---|---|---|
| Primary deficit | Visuospatial dysfunction | Frontal executive dysfunction | High[2] |
| Memory | Encoding deficits, preserved recognition | Retrieval deficits | Moderate |
| Language | Non-fluent aphasia variants | Reduced verbal fluency | Moderate |
| Depression/anxiety | More common | Less common | Moderate[2:1] |
| Apathy | Less common | More common | Moderate |
| Behavioral disinhibition | Less common | Variable | Low |
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:
| 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 |
Essential elements:
Key red flags suggesting CBS over PSP:
Key red flags suggesting PSP over CBS:
MRI is the most accessible and highest-priority imaging modality[3].
CBS findings:
PSP findings:
For automated classification, see Automated MRI Analysis for Atypical Parkinsonism and DTI White Matter Changes in CBS/PSP[3:1].
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 |
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):
For comprehensive imaging biomarker coverage, see MRI Atrophy Patterns in CBS/PSP, Tau PET in CBS/PSP, and Metabolic Imaging PET for CBS/PSP.
CSF and blood biomarkers help differentiate CBS from PSP and rule out mimics[5][6].
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 and Plasma Biomarkers in CBS/PSP.
Genetic architecture shows both overlapping and distinct features between CBS and PSP[7].
| 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 and CBS/PSP Genetic Architecture.
Emerging evidence supports tau seeding assays from skin biopsy for CBS/PSP differentiation[6:1]:
See Skin Biopsy Tau Seeding in CBS/PSP for full details.
| 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 |
| 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) |
The CBD-FRS measures functional impairment specific to CBS:
Used primarily for PSP assessment but informative for differentiation:
For full scale details, see CBD-FRS Diagnostic Page.
This differential diagnosis page should be used in conjunction with the Multimodal Diagnostic Algorithm for CBS and PSP, which provides:
| 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[2:2] |
| 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 |
Armstrong MJ et al. Criteria for the diagnosis of corticobasal syndrome. Neurology. 2023. ↩︎
Niccolini F et al. Cognitive and neuropsychiatric profiles distinguish atypical parkinsonian syndromes. Brain. 2025. ↩︎ ↩︎ ↩︎
Sestini S et al. Automated MRI classification of CBS versus PSP using machine learning. NeuroImage Clinical. 2024. ↩︎ ↩︎
Schneider E et al. Tau PET binding profiles differentiate CBD from PSP and AD. Neurology. 2024. ↩︎
Burre J et al. CSF biomarker profiles in corticobasal syndrome and PSP. Journal of Neurology Neurosurgery and Psychiatry. 2024. ↩︎
Jucker M et al. Blood biomarkers for tauopathies: current state and future directions. Nature Reviews Neurology. 2025. ↩︎ ↩︎
Grauel MK et al. Genetic architecture of corticobasal syndrome and PSP: overlapping and distinct features. Brain. 2024. ↩︎