Progressive Supranuclear Palsy — Richardson Syndrome (PSP-RS) and Corticobasal Syndrome (CBS) are the two most clinically impactful 4-repeat (4R) tauopathies, representing opposite ends of a phenotypic spectrum in the 4R tauopathy family. While both disorders share the fundamental pathology of 4R tau hyperphosphorylation and aggregation, their clinical presentations, anatomical vulnerabilities, and prognostic trajectories differ substantially. This comparison page provides a detailed analysis of the distinguishing features between these two conditions.
Both PSP-RS and CBS share a core molecular pathology that grounds their comparison:
| Feature | PSP Richardson Syndrome | Corticobasal Syndrome |
|---|---|---|
| Onset symmetry | Typically symmetric | Marked asymmetry, especially early |
| Postural instability | Early, frequent falls in year 1 | Variable, typically later onset |
| Eye movement | Vertical supranuclear gaze palsy (VSGP) — hallmark | Absent or mild (slow saccades only) |
| Akinesia pattern | Axial rigidity predominates | Asymmetric limb rigidity, apraxia |
| Cortical signs | Usually absent | Alien limb, apraxia, cortical sensory loss — cardinal |
| Myoclonus | Rare | Common (stimulus-sensitive) |
| Dystonia | Axial, cervical | Asymmetric, often focal (hand/limb) |
| Response to levodopa | Poor to modest (~20-30%) | Minimal to transient [6] |
PSP-RS follows a brainstem-predominant pattern[1:1]:
CBS follows a cortical-subcortical asymmetric pattern[7][8]:
The anatomical distinction is critical: PSP-RS is a subcortical syndrome with brainstem predominance, while CBS is a cortical-subcortical syndrome with asymmetric parietal-motor involvement[7:1].
PSP-RS cognitive features[9]:
CBS cognitive features[10]:
Recent research using seed amplification assays and cryo-EM has revealed distinct tau "strains" between PSP and CBD/CBS[4:1]:
The tau strains propagate through different neural networks[4:2]:
Both disorders show unexpected TDP-43 involvement[11][12]:
| Phase | Time | Characteristic Features |
|---|---|---|
| Prodromal | 1-2 years before diagnosis | Subtle balance issues, reduced blink rate, vague personality changes |
| Early RS | 1-3 years | Classic triad emerges: VSGP, early falls, axial akinesia-rigidity. Independent ambulation |
| Established | 3-6 years | Frequent falls, dysphagia, dysarthria. Wheelchair may be needed |
| Advanced | 6-9 years | Wheelchair-bound, severe dysphagia, minimal verbal output |
| End-stage | >7-9 years | Bedridden, nearly mute, severe cognitive decline |
Key progression features: Early falls (>2-3 in first year) are the single most reliable prognostic indicator. Vertical gaze palsy typically develops within 1-3 years of onset and is never absent in classic RS[5:1].
| Phase | Time | Characteristic Features |
|---|---|---|
| Asymmetric onset | Year 0-1 | One limb affected (usually hand), apraxia, alien limb |
| Lateralized | 1-3 years | Same side remains dominant; may spread to ipsilateral leg |
| Generalization | 3-5 years | Bilateral involvement, cognitive decline accelerates |
| Global | 5-7 years | Symmetric motor involvement, severe cognitive impairment |
| End-stage | 6-9 years | Bedridden, severe dementia |
Key progression features: The asymmetry that defines CBS can persist for years before generalization. Cognitive decline is more prominent earlier than in PSP-RS. The alien limb may evolve from "one limb" to "whole side"[10:1].
Neurofilament Light Chain (NfL)[13]:
Phosphorylated Tau (p-tau181, p-tau217)[14][15]:
MRI characteristics[7:3][8:1]:
FDG-PET patterns[8:2]:
Tau PET (flortaucipir):
Levodopa[6:1]:
For myoclonus (CBS-specific):
For dystonia:
Both conditions face identical challenges in disease-modifying therapy development[9:1]:
Key distinction in trial design: PSP-RS trials can use VSGP as a specific endpoint, while CBS trials must rely on more general motor/cognitive scales. The asymmetry of CBS complicates rating scale design.
When evaluating a patient with features overlapping both conditions, consider:
1. Does the patient have vertical supranuclear gaze palsy?
→ YES: Strongly favors PSP-RS
→ NO: Continue evaluation
2. Are there asymmetric cortical signs (alien limb, apraxia, cortical sensory loss)?
→ YES + no VSGP: Strongly favors CBS
→ NO: Continue to step 3
3. Is the rigidity axial > limb?
→ YES: Favors PSP-RS
→ NO: Favors CBS
4. Are falls within the first year?
→ YES: Favors PSP-RS
→ NO: Favors CBS
5. MRI shows midbrain atrophy with hummingbird sign?
→ YES: Supports PSP-RS
→ NO: Look for asymmetric parietal-motor atrophy → supports CBS
6. CSF NfL very high (>2000 pg/mL)?
→ YES: Suggests AD co-pathology in CBS or aggressive phenotype
→ NO: Consistent with primary 4R tauopathy (either)
The relationship between PSP-RS and CBS reflects the broader 4R tauopathy spectrum:
| Reference | Key Contribution |
|---|---|
| [5:3] | First systematic comparison of PSP-RS vs PSP-P phenotypes |
| [10:3] | Modern CBS diagnostic criteria (Armstrong criteria) |
| [16] | Movement Disorder Society criteria for PSP |
| [1:4] | Comprehensive neuropathology comparison of PSP variants |
| [2:2] | Definitive characterization of CBD as distinct 4R tauopathy |
| [7:4] | Imaging distinction of parietal vs brainstem involvement |
| [4:3] | Tau strain differences between CBS and PSP |
| [13:1] | CSF biomarker differentiation of CBS from PSP |
| [14:1] | p-tau181 in differential diagnosis of CBS vs PSP |
| [8:4] | MDS-PSP criteria predicting amyloid negativity in CBS |
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