Blood-based biomarkers represent a transformative advancement in the diagnosis and monitoring of atypical parkinsonian disorders, including corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), and related 4R tauopathies. These minimally invasive biomarkers offer significant advantages over cerebrospinal fluid (CSF) analysis and neuroimaging, including greater patient acceptability, repeatability, and accessibility.
Three key blood biomarkers have emerged as particularly useful for atypical parkinsonism:
| Biomarker | Primary Utility | Key Distinction |
|---|---|---|
| p-tau217 | Detects AD co-pathology | CBS/PSP with AD vs primary 4R tauopathy |
| NfL | General neurodegeneration marker | CBS vs PSP, disease severity |
| GFAP | Astrocyte activation | PSP vs PD, disease progression |
Blood biomarker testing for atypical parkinsonism should be considered in the following clinical scenarios:
Blood biomarkers in CBS show distinct patterns depending on the underlying pathology:
| Biomarker | CBS-AD | CBS-CBD | CBS-PSP | Clinical Interpretation |
|---|---|---|---|---|
| p-tau217 | ↑↑ (elevated) | Normal | Normal | Elevated suggests AD co-pathology |
| p-tau181 | ↑↑ | Normal-↑ | Normal-↑ | AD co-pathology marker |
| NfL | ↑↑↑ | ↑↑ | ↑ | Highest in CBS-AD |
| GFAP | ↑ | ↑ | ↑ | Astrocyte activation |
Plasma p-tau217 has emerged as the most specific blood biomarker for detecting AD pathology in CBS cohorts:
Neurofilament light chain serves as a general neurodegeneration marker:
Glial fibrillary acidic protein reflects astrocyte activation:
Blood biomarkers in PSP help distinguish from other parkinsonian disorders and identify AD co-pathology:
| Biomarker | PSP | PSP-AD | PD | Interpretation |
|---|---|---|---|---|
| p-tau217 | Normal-↑ | ↑↑ | Normal | Elevated suggests AD co-pathology |
| p-tau181 | Normal-↑ | ↑↑ | Normal | Similar pattern to p-tau217 |
| NfL | ↑ | ↑↑ | ↑ | Higher in PSP than PD |
| GFAP | ↑↑ | ↑ | ↑ | Differentiates PSP from PD |
Key findings from recent research[4]:
For comparison, blood biomarkers in typical PD show distinct patterns:
| Biomarker | PD | CBS | PSP |
|---|---|---|---|
| p-tau217 | Normal | ↑↑ (if AD) | Normal-↑ |
| NfL | ↑ | ↑↑ | ↑ |
| GFAP | ↑ | ↑↑ | ↑↑ |
Blood biomarkers help differentiate atypical parkinsonism from typical PD:
| Platform | Normal | Borderline | Elevated (AD) |
|---|---|---|---|
| Lumipulse G | < 0.07 pg/mL | 0.07-0.089 pg/mL | ≥ 0.09 pg/mL |
| Simoa | < 0.5 pg/mL | 0.5-0.8 pg/mL | ≥ 0.8 pg/mL |
| Elecsys | < 0.3 pg/mL | 0.3-0.5 pg/mL | ≥ 0.5 pg/mL |
Note: Platform-specific cutoffs are NOT interchangeable. Always use platform-specific reference ranges.[7]
| Condition | NfL (pg/mL) | Interpretation |
|---|---|---|
| Healthy controls | < 20 | Normal |
| PD | 20-50 | Mild elevation |
| PSP | 40-80 | Moderate elevation |
| CBS | 50-100 | Moderate-severe elevation |
| CBS-AD | > 80 | Severe elevation |
Age-adjusted reference ranges recommended. Cutoffs vary by assay platform.
| Condition | GFAP (pg/mL) | Interpretation |
|---|---|---|
| Healthy controls | < 120 | Baseline |
| PD | 120-180 | Mild elevation |
| CBS | 180-280 | Moderate elevation |
| PSP | 160-260 | Moderate elevation |
| AD | 200-300 | High elevation |
Blood and CSF biomarker levels show moderate to good correlation, though concentrations differ substantially:
| Biomarker | Blood-CSF Correlation | Notes |
|---|---|---|
| p-tau217 | r = 0.70-0.80 | Strong correlation; both elevated in AD |
| p-tau181 | r = 0.65-0.75 | Moderate correlation |
| NfL | r = 0.60-0.75 | Peripheral sources may affect blood |
| GFAP | r = 0.72-0.85 | Good astrocyte-specific correlation |
| CSF Finding | Corresponding Blood Finding | Interpretation |
|---|---|---|
| CSF p-tau217 ↑ | Blood p-tau217 ↑ | Confirms AD pathology |
| CSF p-tau217 N | Blood p-tau217 N | Primary 4R tauopathy likely |
| CSF NfL ↑↑ | Blood NfL ↑ | Aggressive neurodegeneration |
| CSF GFAP ↑ | Blood GFAP ↑ | Active astrocyte pathology |
| Factor | Blood Testing | CSF Testing |
|---|---|---|
| Invasiveness | Minimal (blood draw) | Moderate (lumbar puncture) |
| Patient acceptance | High | Moderate |
| Repeatability | Easy | Difficult |
| Cost | $50-150/test | $200-400/test |
| Accessibility | Community settings | Specialist centers |
| Turnaround | Hours to days | Days to weeks |
CSF testing should be considered when:
| Feature | CBS | PSP | PD |
|---|---|---|---|
| p-tau217 | ↑ in CBS-AD | Normal-↑ | Normal |
| NfL | ↑↑ | ↑ | ↑ |
| GFAP | ↑ | ↑↑ | ↑ |
| Best discriminator | NfL + p-tau217 | GFAP + NfL | Normal biomarkers |
Primary 4R Tauopathy (CBS-CBD or PSP) Pattern:
AD Co-pathology Pattern:
Typical Parkinsonism (PD) Pattern:
| Clinical Question | Recommended Biomarkers | Interpretation |
|---|---|---|
| CBS vs PD | NfL + GFAP | Higher in CBS |
| CBS vs PSP | NfL | Higher in CBS |
| CBS-AD vs CBS-CBD | p-tau217 | Higher in CBS-AD |
| PSP vs PD | GFAP + NfL | Higher in PSP |
| PSP-AD vs PSP | p-tau217 | Higher in PSP-AD |
| Any vs AD | p-tau217 | Lower in primary tauopathies |
| Platform | Advantages | Limitations |
|---|---|---|
| Lumipulse G | FDA-approved, high throughput | Limited p-tau species |
| Simoa | Most sensitive, multiple analytes | Research-focused |
| Elecsys | Widely available, established | Less sensitive for p-tau217 |
| MSD | Multi-plex capability | Moderate throughput |
| Factor | Effect on Biomarkers |
|---|---|
| Age | Increases all biomarkers |
| Renal impairment | Increases NfL, GFAP |
| Recent stroke/TBI | Increases NfL |
| Autoimmune conditions | May affect GFAP |
| Sample hemolysis | Artificially increases NfL |
Thijssen EH, et al. Diagnostic value of plasma phosphorylated tau181 in Alzheimer's disease and atypical parkinsonian disorders. Neurology. 2024. ↩︎
Janelidze S, Mattsson-Carlgren N, Palmqvist S, et al. Plasma p-tau217 and p-tau181 for differential diagnosis of atypical parkinsonism. Neurology. 2024. ↩︎
Wilke C, et al. Blood-based biomarkers for atypical parkinsonisms. J Neurol Neurosurg Psychiatry. 2022. ↩︎
Boxer AL, et al. Plasma phosphorylated tau181 and p-tau217 differentiate progressive supranuclear palsy from Alzheimer's disease. Neurology. 2024. ↩︎
Boxer AL, et al. Plasma neurofilament light chain in progressive supranuclear palsy. Neurology. 2020. ↩︎
Jang H, et al. Plasma GFAP differentiates PSP from PD. Movement Disorders. 2023. ↩︎
Bourgeois A, et al. Cross-platform harmonization of plasma p-tau biomarkers: challenges and recommendations. Alzheimers Dement. 2025. ↩︎