Multiple System Atrophy

Multiple System Atrophy (MSA)

Overview

Multiple System Atrophy (MSA) is a rare, rapidly progressive, fatal neurodegenerative disorder classified within the synucleinopathies — a group of diseases characterized by the abnormal accumulation of alpha-synuclein protein in neurons and glia[@fedorov2022]. MSA is distinguished from [Parkinson's disease](/diseases/parkinsons-disease) and other synucleinopathies by the predominant deposition of alpha-synuclein in oligodendrocytes, forming characteristic glial cytoplasmic inclusions (GCIs), rather than primarily in neurons as in PD[@jec2022].

MSA presents with a combination of:

• Parkinsonism (poor levodopa response, symmetric onset, early falls)
• Cerebellar ataxia (gait instability, limb incoordination, dysarthria)
• Autonomic failure (orthostatic hypotension, urinary dysfunction, erectile dysfunction)

The disease is classified into two main subtypes based on the predominant motor phenotype:

• MSA-P (parkinsonian-predominant): ~60-70% of cases, features bradykinesia, rigidity, and tremor resembling PD
• MSA-C (cerebellar-predominant): ~30-40% of cases, features prominent cerebellar ataxia

MSA progresses more rapidly than PD, with median survival of 6-10 years from symptom onset. Cognitive impairment, while less prominent than in [Dementia With Lewy Bodies](/diseases/dementia-with-lewy-bodies), occurs in a subset of patients.

Epidemiology

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Multiple System Atrophy (MSA)

Overview

Multiple System Atrophy (MSA) is a rare, rapidly progressive, fatal neurodegenerative disorder classified within the synucleinopathies — a group of diseases characterized by the abnormal accumulation of alpha-synuclein protein in neurons and glia[@fedorov2022]. MSA is distinguished from [Parkinson's disease](/diseases/parkinsons-disease) and other synucleinopathies by the predominant deposition of alpha-synuclein in oligodendrocytes, forming characteristic glial cytoplasmic inclusions (GCIs), rather than primarily in neurons as in PD[@jec2022].

MSA presents with a combination of:

• Parkinsonism (poor levodopa response, symmetric onset, early falls)
• Cerebellar ataxia (gait instability, limb incoordination, dysarthria)
• Autonomic failure (orthostatic hypotension, urinary dysfunction, erectile dysfunction)

The disease is classified into two main subtypes based on the predominant motor phenotype:

• MSA-P (parkinsonian-predominant): ~60-70% of cases, features bradykinesia, rigidity, and tremor resembling PD
• MSA-C (cerebellar-predominant): ~30-40% of cases, features prominent cerebellar ataxia

MSA progresses more rapidly than PD, with median survival of 6-10 years from symptom onset. Cognitive impairment, while less prominent than in [Dementia With Lewy Bodies](/diseases/dementia-with-lewy-bodies), occurs in a subset of patients.

Epidemiology

| Feature | Value |
|---------|-------|
| Prevalence | 2-5 per 100,000 |
| Annual incidence | 0.6 per 100,000 |
| Mean age at onset | 53-64 years |
| Gender distribution | Slight male predominance (1.3-1.5:1) |
| Geographic variation | MSA-C more common in Japan; MSA-P more common in Western countries |
| Disease duration | Median 6-10 years from onset |

MSA is often misdiagnosed as PD early in the disease course. Key distinguishing features include symmetric onset, poor levodopa response, early autonomic failure, and rapid progression.

Pathophysiology

Glial Cytoplasmic Inclusions (GCIs)

The pathognomonic feature of MSA is the presence of glial cytoplasmic inclusions (GCIs) — aggregated alpha-synuclein deposits within oligodendrocytes[@jec2022]. Unlike the Lewy bodies found in PD, which are neuronal, GCIs are the defining neuropathological hallmark of MSA:

Oligodendrocyte Dysfunction

Oligodendrocytes in MSA show a distinctive vulnerability to alpha-synuclein toxicity[@refahi2024]:

GCI accumulation: Alpha-synuclein aggregates form within the oligodendrocyte soma, displacing normal cytoplasm

Myelin protein disruption: GCIs contain not only alpha-synuclein but also tau, tubulin, and heat-shock proteins

Myelin instability: GCIs disrupt the normal myelin maintenance function of oligodendrocytes

axon-glial uncoupling: The oligodendrocyte-axon metabolic support relationship is impaired

Cell death: Oligodendrocytes eventually die, leading to demyelination and axonal degeneration

The oligodendrocyte dysfunction in MSA may follow a "dying-back" oligodendrogliopathy pattern, where distal axonal degeneration precedes myelin breakdown.

Neuronal Involvement

While GCIs are the hallmark, MSA also involves neuronal alpha-synuclein pathology[@wu2025]:

• Neuronal cytoplasmic inclusions (NCIs): Neurons contain less abundant alpha-synuclein inclusions
• Neuronal loss: Particularly in basal ganglia, pontine nuclei, inferior olivary nucleus, and Purkinje cells of the cerebellum
• Axonal degeneration: Secondary to oligodendrocyte loss and demyelination
• Neural circuitry disruption: Motor and autonomic circuits are affected through multiple mechanisms

Propagation Hypothesis

The relationship between glial and neuronal alpha-synuclein in MSA is a subject of active investigation[@wu2025]:

Glial-to-neuronal propagation model (dominant hypothesis):

Oligodendrocytes accumulate alpha-synuclein from extracellular sources or intracellular aggregation

GCI-bearing oligodendrocytes become dysfunctional and die

Dying oligodendrocytes release alpha-synuclein aggregates into the extracellular space

Neurons take up extracellular alpha-synuclein, leading to neuronal pathology

This creates a feedforward cycle driving progressive neurodegeneration

Neuronal-to-glial propagation model (alternative):

Neurons are the primary site of alpha-synuclein aggregation

Aggregates are transferred to oligodendrocytes via extracellular vesicles

Oligodendrocytes cannot efficiently process the aggregate load

GCI formation ensues, followed by oligodendrocyte death and demyelination

Both models are supported by experimental data, and the truth may involve elements of both.

Clinical Features

Autonomic Failure

Autonomic dysfunction is a core feature of MSA and is often the earliest and most disabling manifestation[@krismer2023]:

Cardiovascular Autonomic Failure

• Neurogenic orthostatic hypotension (nOH): Sustained drop in systolic BP (>=20 mmHg) or diastolic BP (>=10 mmHg) upon standing, without appropriate compensatory tachycardia
• Post-prandial hypotension: Worsening of orthostatic hypotension after meals
• Supine hypertension: Paradoxically elevated BP when lying down
• Baroreflex failure: Impaired reflex-mediated heart rate and vasomotor responses

Urinary Dysfunction

• Early-stage urgency and frequency: Often misdiagnosed as prostate or bladder conditions
• Nocturia: Multiple nighttime awakenings to urinate
• Urge incontinence: Progressive loss of bladder control
• Retention: May progress to urinary retention requiring catheterization

Erectile Dysfunction

• Often an early symptom, preceding other MSA features by years
• Severe and treatment-resistant

Gastrointestinal Dysfunction

• Constipation: Very common, often severe
• Delayed gastric emptying: Nausea, early satiety
• Fecal incontinence: Occurs in advanced stages

Motor Features

MSA-P (Parkinsonian-Predominant)

• Bradykinesia: Slowness of movement, reduced amplitude
• Rigidity: Cogwheel or lead-pipe, typically symmetric
• Postural instability: Early falls (within 1-2 years of onset), in contrast to PD
• Tremor: May have tremor, but typically postural/action rather than resting tremor of PD
• Poor levodopa response: Unlike PD, MSA shows minimal or transient response to levodopa
• Rapid progression: Motor symptoms worsen faster than in PD

MSA-C (Cerebellar-Predominant)

• Gait ataxia: Wide-based, unsteady gait, frequent falls
• Limb ataxia: Incoordination, dysmetria on finger-nose and heel-shin testing
• Scanning dysarthria: Slow, slurred, monotonous speech with irregular rhythm
• Nystagmus: Horizontal, vertical, or downbeat nystagmus
• Dysphagia: Difficulty swallowing, risk of aspiration
• Oculomotor abnormalities: Impaired smooth pursuit, gaze-evoked nystagmus

Sleep Disorders

REM Sleep Behavior Disorder (RBD)

• Present in 50-70% of MSA patients[@graziollo2023]
• Often precedes motor symptoms by years
• More violent than in PD (patients may fall out of bed, injury themselves or partners)
• Phenomenology: complex movements during REM sleep, accompanied by vivid dreams

Sleep-Disordered Breathing

• Central sleep apnea
• Stridor (inspiratory sound due to laryngeal abductor dysfunction) — medical emergency
• Sleep fragmentation, excessive daytime sleepiness

Neuropsychiatric Features

• Depression: Common, often severe
• Anxiety: Generalized anxiety, panic attacks
• Cognitive impairment: Variable, typically subcortical pattern (slowed processing, executive dysfunction). Prominent dementia suggests DLB instead
• Apathy: Loss of motivation, interest

Subtypes and Diagnosis

Clinical Subtypes

| Feature | MSA-P | MSA-C |
|---------|-------|-------|
| Motor predominant | Parkinsonism (bradykinesia, rigidity, tremor) | Cerebellar ataxia (gait, limb, speech) |
| Proportion | ~60-70% | ~30-40% |
| Geographic distribution | More common in Western countries | More common in Japan |
| MRI findings | Putaminal atrophy, hot cross bun sign | Pontocerebellar atrophy, hot cross bun sign |
| Autonomic failure | Present, often severe | Present, often severe |

Diagnostic Criteria

The 2022 International MSA Consensus Criteria:

Definite MSA: Autopsy confirmation Probable MSA:

• Autonomic failure with urinary dysfunction or orthostatic hypotension AND
• Parkinsonism (MSA-P) OR cerebellar syndrome (MSA-C)
• Additional features supporting diagnosis

Possible MSA:

• Autonomic failure with urinary dysfunction or orthostatic hypotension AND
• Parkinsonism (MSA-P) OR cerebellar syndrome (MSA-C)
• Less certain features (may be early disease)

Imaging Findings

MRI

| Finding | Description | Clinical Significance |
|---------|-------------|----------------------|
| Hot cross bun sign | Cross-shaped hyperintensity in pons on T2/FLAIR | Highly characteristic of MSA (but not specific) |
| Putaminal atrophy | Atrophy and hypointensity of posterior putamen | More prominent in MSA-P |
| Pontocerebellar atrophy | Atrophy of pons and cerebellar hemispheres | More prominent in MSA-C |
| Middle cerebellar peduncle atrophy | Reduced volume of MCP | Supports MSA-C |
| "Sleeping" substantia nigra | Loss of nigrosomal hyperintensity on SWI | Distinguishes MSA from PD[@sato2023] |

PET/SPECT

• Dopamine transporter imaging (DaTSCAN/I-123-FP-CIT): Reduced uptake in striatum, but cannot reliably distinguish MSA from PD
• FDG-PET: Hypometabolism in cerebellum (MSA-C), brainstem, and putamen
• Alpha-synuclein PET tracers: In development; may eventually allow specific imaging of GCI burden

Biomarkers

CSF Biomarkers

| Biomarker | Change in MSA | Utility |
|-----------|--------------|---------|
| Neurofilament light chain (NfL) | Elevated | Marker of neurodegeneration; correlates with disease severity and progression[@sekimoto2022] |
| Alpha-synuclein (total) | Reduced | May distinguish from PD, but not specific |
| Alpha-synuclein seed amplification (RT-QuIC) | Positive | Detects alpha-synuclein aggregation in CSF |
| Tau (total) | Elevated | Non-specific marker of neurodegeneration |
| Beta-amyloid 1-42 | Normal or reduced | Helps distinguish from AD co-pathology |
| 14-3-3 protein | May be elevated | Non-specific, sometimes elevated in rapid neurodegeneration |

Distinguishing from Parkinson's Disease

| Feature | MSA | Parkinson's Disease |
|---------|-----|---------------------|
| Levodopa response | Poor/minimal | Good (initially) |
| Onset symmetry | Symmetric | Often asymmetric |
| Disease progression | Rapid (6-10 yr) | Slow (15+ yr) |
| Autonomic failure | Early and severe | Late and mild |
| Postural instability | Early (within 1-2 yr) | Late |
| Cognitive impairment | Late, subcortical | Late (PDD) or early (DLB) |
| RBD | Common (50-70%) | Very common (60-80%) |
| MRI: Hot cross bun sign | Present in ~50-70% | Absent |
| MRI: Putaminal hypointensity | Present | Absent or less severe |

Molecular Mechanisms

Alpha-Synuclein Aggregation

The alpha-synuclein in MSA shows biochemical differences from PD alpha-synuclein:

• More phosphorylated at Serine-129 (pSer129-αSyn)
• Forms more compact, less fibrillar aggregates
• Shows greater tendency to form oligomers rather than large fibrils

The structural differences between MSA and PD alpha-synuclein may explain the different cell types primarily affected (oligodendrocytes vs. neurons).

Myelin Dysfunction

Oligodendrocyte dysfunction leads to myelin pathology[@refahi2024]:

• Myelin basic protein (MBP): May be reduced in areas of GCI accumulation
• Myelin-associated glycoprotein (MAG): Affected by oligodendrocyte dysfunction
• CNPase activity: Reduced in regions with high GCI burden
• White matter hyperintensities: Visible on MRI in advanced disease

Mitochondrial Dysfunction

• COQ2 mutations: Variants in the coenzyme Q10 biosynthetic gene COQ2 increase MSA risk[@fan2019]
• Complex I deficiency: Observed in MSA brain tissue
• Oxidative stress: Elevated markers of oxidative damage in MSA brain
• Coenzyme Q10 deficiency: May contribute to neurodegeneration; trials of CoQ10 supplementation in MSA ongoing

Genetic Risk Factors

• COQ2: Mitochondrial coenzyme Q10 biosynthesis gene; variants associated with increased MSA risk
• SNCA: Alpha-synuclein gene; multiplications and point mutations associated with rare MSA cases
• GBA: Glucocerebrosidase gene; variants increase risk of both PD and MSA
• MAPT: Tau gene; H1 haplotype associated with increased risk in some cohorts
• SCARB2: Lysosomal receptor for alpha-synuclein uptake; variants may influence MSA risk

Therapeutic Approaches

Symptomatic Treatment

Parkinsonism

• Levodopa/carbidopa: Modest, often transient benefit; many patients discontinue due to lack of response or complications (dyskinesias, hallucinations)
• Dopamine agonists: Limited benefit, more side effects than in PD
• MAO-B inhibitors: May provide modest benefit

Autonomic Failure

• Orthostatic hypotension: Salt and fluid intake, head-up tilt during sleep, compression garments, fludrocortisone, midodrine, droxidopa
• Supine hypertension: Head elevation during sleep, short-acting antihypertensives at night
• Urinary dysfunction: Bladder training, antimuscarinics (oxybutynin, tolterodine), intermittent catheterization
• Constipation: High-fiber diet, adequate hydration, laxatives (polyethylene glycol), prokinetics

Sleep Disorders

• RBD: Clonazepam (0.25-0.5 mg), melatonin (3-15 mg), sleep hygiene
• Stridor: Continuous positive airway pressure (CPAP), vocal cord augmentation in severe cases, tracheostomy as last resort

Disease-Modifying Approaches

Alpha-Synuclein Targeting

• Immunotherapy: Active and passive vaccines targeting alpha-synuclein in clinical trials
• Small molecule aggregation inhibitors: Modulating alpha-synuclein aggregation pathways
• Nucleic acid approaches: ASO and siRNA targeting SNCA mRNA (in early development)

Neuroprotection

• Coenzyme Q10: Clinical trials showed some slowing of disease progression at high doses (300 mg/day)[@ahmed2024]
• Riluzole: glutamate release inhibitor; trials in MSA
• Mesenchymal stem cells: Investigational approach for neuroprotection

Supportive Care

• Physical therapy: Gait training, balance exercises, fall prevention
• Occupational therapy: Adaptive equipment, home modifications
• Speech therapy: For dysarthria, dysphagia
• Nutritional support: Dietary modifications, PEG feeding in advanced disease
• Psychological support: For patient and caregivers

Research Challenges and Open Questions

Early diagnosis: How can MSA be distinguished from PD in the first 2-3 years, before classic features emerge?

GCI vs. NCI: Chicken or egg?: Does oligodendrocyte pathology drive neuronal loss, or vice versa? What is the primary insult in MSA?

Why oligodendrocytes?: What makes oligodendrocytes particularly vulnerable to alpha-synuclein accumulation in MSA compared to PD?

Biomarker development: Can we develop a specific diagnostic biomarker for MSA before autopsy? Alpha-synuclein seed amplification shows promise but needs validation.

Therapeutic targets: What pathways beyond alpha-synuclein are most promising for disease modification? CoQ10, mitochondrial function, myelin repair?

Heterogeneity: MSA-P vs MSA-C represent different clinical manifestations of the same disease or distinct subtypes? Can we understand the molecular basis of this subtype variation?

Co-pathology: How common is co-occurrence of MSA pathology with AD or DLB pathology? How does co-pathology affect clinical presentation and progression?

Propagation mechanisms: Can we determine the cell-to-cell transmission pathways for alpha-synuclein in MSA? Can we block them therapeutically?

See Also

• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Dementia With Lewy Bodies](/diseases/dementia-with-lewy-bodies)
• [Alpha-Synuclein and Synucleinopathies](/mechanisms/alpha-synuclein)
• [Oligodendrocyte Dysfunction in Neurodegeneration](/mechanisms/oligodendrocyte-dysfunction)
• [Autonomic Failure in Neurodegeneration](/mechanisms/autonomic-dysfunction)
• [Neurodegeneration with Brain Iron Accumulation](/mechanisms/iron-dysregulation)
• [REM Sleep Behavior Disorder](/mechanisms/rem-sleep-behavior-disorder)
• [Cerebellar Ataxia in Neurodegeneration](/mechanisms/cerebellar-ataxia)
• [Glial Cells in Neurodegeneration](/mechanisms/neuroinflammation)