What is progressive supranuclear palsy?

What is Progressive Supranuclear Palsy?

Progressive supranuclear palsy (PSP), also known as Steele-Richardson-Olszewski syndrome, is the most common atypical Parkinsonism—a neurodegenerative tauopathy characterized by abnormal tau protein accumulation in the brain, presenting classically with unexplained falls, gait instability, and vertical supranuclear gaze palsy 1.

Disease Classification and Pathophysiology

PSP belongs to the "Parkinson-plus" syndromes or atypical Parkinsonisms, distinguished from typical Parkinson's disease by:

• Pathologic mechanism: PSP is a tauopathy where tau proteins abnormally accumulate in different brain regions, fundamentally different from Parkinson's disease (which is a synucleinopathy with Lewy body deposits) 1
• Affected brain regions: Neuronal death, gliosis, and tau aggregates appear as globose neurofibrillary tangles primarily in the subthalamic nucleus, substantia nigra, globus pallidus, basal ganglia, brainstem, and cerebellum 2, 3

Epidemiology

• Prevalence: Approximately 5-6.4 per 100,000 population, making it the most common atypical Parkinsonism 1, 4
• Age of onset: Typically presents in the sixth or seventh decade of life, with mean age of onset at 63 years 1
• Geographic variation: Influenced by genetic predispositions (notably the MAPT H1 haplotype), environmental factors, and healthcare infrastructure 4

Clinical Presentation

Early Disease Features

The hallmark early presentation is a lurching gait with axial dystonia manifested as unexplained falls—this is the key distinguishing feature from typical Parkinson's disease 1. Patients present with:

• Postural instability and frequent falls: Often the first and most prominent symptom
• Early ocular symptoms: Blurred vision and slow saccades (eye movements)
• Axial rigidity: Stiffness predominantly affecting the trunk and neck

Classic Later Features

• Vertical supranuclear gaze palsy: The pathognomonic finding, but typically appears later in the disease course, not at onset 1
• Pseudobulbar palsy: Difficulty with speech and swallowing
• Dysarthria: Speech difficulties
• Cognitive impairment: Frontal lobe dysfunction, dementia, amnesia, irritability, loss of interest 3, 5

Motor Symptoms

PSP demonstrates classic Parkinsonian features (bradykinesia and rigidity) but with critical differences 1:

• Tremor is less prominent than in typical Parkinson's disease
• Postural instability occurs much earlier
• Poor or absent response to levodopa therapy 5

Clinical Phenotypes

PSP manifests in multiple variants 4, 6:

• PSP-Richardson's syndrome (PSP-RS): Classic presentation with rapid progression and shorter survival (5-7 years)
• PSP-Parkinsonism (PSP-P): More Parkinson-like features with milder course (8-12 years survival)
• PSP-Progressive gait freezing (PSP-PGF): Predominant gait dysfunction
• PSP-Corticobasal syndrome (PSP-CBS): Overlapping features with corticobasal degeneration

Diagnostic Approach

Clinical Diagnosis Challenges

Diagnosis is challenging because clinical features alone are insufficient—definitive diagnosis requires postmortem pathological confirmation 2, 6. The 2017 Movement Disorders Society PSP criteria have improved recognition of diverse phenotypes 6.

Imaging Findings

MRI is the optimal imaging modality 1:

• Regional volume loss patterns characteristic of PSP
• Midbrain atrophy
• Superior cerebellar peduncle atrophy

FDG-PET/CT shows characteristic patterns 1:

• Hypometabolism in medial frontal and anterior cingulate cortices
• Striatal and midbrain hypometabolism

Important Caveat

Biomarkers in imaging and CSF are not sufficient to support diagnosis alone—they help rule out similar pathologies but lack specificity for PSP 2, 7.

Prognosis

• Disease duration: Mean survival approximately 5-7 years for PSP-RS, 8-12 years for PSP-P 4
• Progressive course: Relentlessly progressive with no current disease-modifying therapies 7
• Cause of death: Often related to complications of immobility, dysphagia, and aspiration

Treatment Approach

There is no curative therapy for PSP—all available treatments are palliative and symptomatic 3, 6:

• Levodopa trial: May be attempted but typically shows absent or only transient response 5
• Symptomatic management: Serotonin antagonists, α2 receptor antagonists have been tried 3
• Multidisciplinary supportive care: Physical therapy, speech therapy, swallowing evaluation
• Emerging therapies: Current clinical trials target tau aggregation through immunotherapy and gene therapy, though prior trials have been disappointing 7

Key Distinguishing Features from Parkinson's Disease

1. Early falls and postural instability (not late-stage as in PD)
2. Vertical gaze palsy (absent in PD)
3. Poor levodopa response (PD typically responds well)
4. Axial > limb rigidity (PD shows more limb involvement)
5. Tau pathology (PD has synuclein/Lewy body pathology)