Neuroimaging plays a crucial role in the diagnosis, differential diagnosis, and monitoring of progressive supranuclear palsy (PSP). Both conventional and advanced neuroimaging techniques provide valuable information about the structural and functional changes that characterize PSP.
Studies in Japanese, Korean, and Chinese populations have shown that midbrain to pons ratios may differ from Caucasian cohorts due to population-specific brain size variations. The MR parkinsonism index (MRPI) has been validated in Asian cohorts, showing similar diagnostic utility but with adjusted cutoffs for optimal sensitivity. Tau PET binding patterns in Chinese patients show comparable subcortical dominance to Western populations.
Conventional MRI findings in PSP include:
- Midbrain atrophy: The "Hummingbird sign" or "Penguin sign" on sagittal T1-weighted images, reflecting atrophy of the midbrain tegmentum
- Superior cerebellar peduncle atrophy: Visible on axial images, reflecting degeneration of efferent cerebellar pathways
- Third ventricle enlargement: Due to thalamic and hypothalamic atrophy
- Frontal lobe atrophy: Particularly in the precentral and superior frontal gyri
- Red nucleus hyperintensity: On T2-weighted images in the red nucleus
| Sign |
Description |
Sensitivity |
Specificity |
| Hummingbird sign |
Midbrain beak-like appearance |
50-70% |
High |
| Morning glory sign |
Flattened dorsal midbrain |
40-60% |
Moderate |
| Mouse sign |
Atrophic midbrain |
50-70% |
Moderate |
| Hot cross bun sign |
Pontine cross-shaped hyperintensity |
Variable |
Low (also in MSA) |
Advanced quantitative measures include:
- Midbrain to pons ratio: Reduced in PSP vs. other parkinsonian disorders
- Magnetic resonance parkinsonism index (MRPI): Combines multiple regional measurements
- Superior cerebellar peduncle width: Correlates with clinical severity
- Fronto-occipital fasciculus integrity: Assessed via diffusion tensor imaging
DTI reveals microstructural changes in PSP:
DTI metrics correlate with clinical measures of disease severity and progression.
Tau PET ligands provide insights into tau pathology distribution:
- ^18F-AV-1451 (Flortaucipir): Binds to paired helical filament tau, showing elevated binding inPSP subcortical regions
- ^18F-APN-1607: Second-generation tau PET ligand with improved sensitivity
Tau PET findings in PSP:
- Elevated binding in basal ganglia, thalamus, brainstem
- Less cortical binding compared to Alzheimer's disease
- Correlates with clinical phenotype and disease duration
FDG-PET reveals hypometabolism patterns:
The FDG-PET pattern helps differentiate PSP from:
- Parkinson's disease (predominant basal ganglia hypometabolism)
- Multiple system atrophy (cerebellar or brainstem hypometabolism patterns)
- DAT PET/SPECT: Shows reduced dopamine transporter binding in striatum
- Helps differentiate PSP from essential tremor
- Correlates with disease severity
DWI findings include:
- Restricted diffusion in the superior cerebellar peduncle
- ADC maps: Elevated ADC values in affected regions
- Utility in differential diagnosis: Helps distinguish PSP from other parkinsonian disorders
MRS reveals metabolic changes:
- Reduced N-acetylaspartate (NAA) in frontal cortex and basal ganglia
- Elevated choline in midbrain
- Reduced NAA/Cr ratio correlates with disease severity
- Iron deposition: Increased iron in basal ganglia and red nucleus
- Correlates with disease severity
- May serve as a biomarker of neurodegeneration
- Elevated free water in:
- Superior cerebellar peduncles
- White matter tracts
- Sensitive to early disease changes
- Disrupted functional connectivity in:
- Frontoparietal networks
- Salience network
- Default mode network
- Correlates with cognitive impairment
The MDS clinical diagnostic criteria for PSP incorporate neuroimaging:
- Probable PSP: Supportive MRI findings (midbrain atrophy, hummingbird sign)
- Possible PSP: Imaging findings supportive but not conclusive
Neuroimaging biomarkers serve as:
- Progression markers: Serial MRI/DTI measures track disease progression
- Biomarker endpoints: In clinical trials
- Predictive markers: Baseline imaging predicts clinical outcomes
- Treatment monitoring: Imaging endpoints for disease-modifying therapy trials
Neuroimaging biomarkers are increasingly used as endpoints in clinical trials for PSP:
- Anti-tau therapies: Tau PET serves as direct target engagement biomarker
- Neuroprotective agents: DTI and free water imaging track microstructural changes
- Symptomatic treatments: Structural MRI monitors for treatment-related brain changes
- Dose-finding: Imaging biomarkers help determine optimal biologic doses
¶ Cost and Accessibility Analysis
| Modality |
Approximate Cost (USD) |
Accessibility |
Clinical Utility Score |
| Structural MRI |
$500-1,500 |
Moderate-High |
High |
| DTI |
$800-2,000 |
Moderate |
High |
| FDG-PET |
$2,000-4,000 |
Moderate |
High |
| Tau PET |
$3,000-6,000 |
Low-Moderate |
High |
| DAT-SPECT |
$1,500-3,000 |
Moderate |
Moderate |
| QSM |
$800-2,000 |
Moderate |
Moderate |
| Free Water Imaging |
$800-2,000 |
Moderate |
Moderate |
- Structural MRI remains the most cost-effective first-line imaging modality for PSP diagnosis, with widespread availability
- DTI adds diagnostic specificity for differential diagnosis at moderate additional cost
- Tau PET provides highest specificity for tau pathology but at significant cost and limited availability
- FDG-PET offers good balance of diagnostic utility and cost for PSP characterization
- Automated imaging analysis for diagnosis
- Predictive models for disease progression
- Integration with clinical data
- Combined PET/MRI for comprehensive assessment
- Tau PET + structural MRI correlation
- Functional + structural integration