Striatonigral degeneration (SND) is the neuropathological hallmark of the parkinsonian variant of multiple system atrophy (MSA-P) and represents one of the most distinctive patterns of neurodegeneration in the atypical parkinsonian disorders [1]. The term describes the progressive degeneration of the striatum (caudate nucleus and putamen) and the substantia nigra pars compacta, leading to severe dopaminergic deficits that underlie the parkinsonian features of MSA [2].
Multiple system atrophy is a progressive neurodegenerative disorder characterized by varying combinations of parkinsonian features, cerebellar ataxia, and autonomic dysfunction. The disease was first described by Graham and Oppenheimer in 1969 as a condition encompassing striatonigral degeneration, olivopontocerebellar atrophy, and autonomic failure. Modern classification recognizes two main subtypes: MSA-P (parkinsonian) and MSA-C (cerebellar), with SND being the pathological substrate of MSA-P.
The nigrostriatal dopaminergic pathway originates in the substantia nigra pars compacta (SNc) and projects to the striatum (caudate nucleus and putamen). This pathway is critical for: [2:1]
The nigrostriatal pathway represents the primary motor circuit connecting the basal ganglia to cortical regions. Dopaminergic neurons in the SNc send dense projections to the striatum, where they modulate the activity of medium spiny neurons through D1 and D2 dopamine receptors. This modulation is essential for initiating and controlling voluntary movements, with degeneration of this pathway resulting in the bradykinesia and rigidity characteristic of parkinsonian disorders.
In MSA, this pathway undergoes severe degeneration, leading to the characteristic parkinsonian syndrome [3]. The pattern of degeneration differs from Parkinson's disease, with more widespread involvement of both the striatum and substantia nigra, reflecting the underlying oligodendroglial pathology that drives neuronal loss in MSA.
The striatum is the primary input nucleus of the basal ganglia and receives: [4]
The striatum contains two major populations of medium spiny neurons:
In SND, both populations are affected, leading to profound motor dysfunction. The striatum integrates information from multiple brain regions and uses this integration to modulate movement through the direct and indirect pathways. Loss of dopaminergic input disrupts this balance, favoring the indirect pathway and resulting in the hypokinetic movement disorder seen in MSA-P.
The primary pathological hallmark of striatonigral degeneration is the abnormal accumulation of phosphorylated alpha-synuclein (pSer129) in oligodendroglial cells, forming glial cytoplasmic inclusions (GCIs) [3:1][5]. These inclusions:
Unlike Parkinson's disease, where alpha-synuclein inclusions primarily affect neurons, MSA is characterized by oligodendroglial pathology that is thought to be primary rather than secondary [6][7]. The accumulation of alpha-synuclein in oligodendrocytes represents a fundamental difference in the pathogenesis of these related disorders and may explain the more rapid progression and broader clinical phenotype of MSA.
The mechanism by which alpha-synuclein accumulates in oligodendrocytes remains an area of active investigation. Several hypotheses have been proposed, including impaired autophagy, altered alpha-synuclein clearance, and neuronal-to-oligodendroglial transmission [8]. The oligodendroglial expression of alpha-synuclein is normally low, suggesting that pathogenic mechanisms involve either uptake from extracellular sources or derepression of endogenous expression.
In SND, the pattern of neuronal loss follows a characteristic sequence:
The regional vulnerability within the striatum correlates with the density of dopaminergic innervation and the distribution of oligodendroglial pathology. The posterior-dorsal putamen, which receives the densest dopaminergic input, shows the most severe degeneration, consistent with the critical role of dopamine in maintaining striatal neuron viability.
Multiple mechanisms contribute to neuronal death in SND [9]:
These mechanisms are interconnected and create a self-perpetuating cycle of neurodegeneration. For example, mitochondrial dysfunction leads to increased ROS production, which promotes oxidative damage to proteins and lipids, further impairing mitochondrial function. Similarly, neuroinflammation leads to the release of pro-inflammatory cytokines that can damage neurons and activate additional microglia.
Glial cytoplasmic inclusions (GCIs) are the hallmark pathological lesion of MSA and distinguish this disorder from other synucleinopathies [6:1]. These inclusions are composed primarily of aggregated alpha-synuclein filaments within the cytoplasm of oligodendrocytes. The morphological and biochemical properties of GCIs differ from Lewy bodies found in PD, suggesting that different strains of alpha-synuclein may underlie these disorders.
GCI Morphology:
GCI Composition:
The formation of GCIs appears to compromise oligodendrocyte function, leading to impaired myelin maintenance and support of neuronal axons. This oligodendroglial dysfunction then contributes to secondary neuronal degeneration through mechanisms including trophic support deficiency, impaired axonal transport, and increased vulnerability to metabolic stress.
The concept of prion-like propagation has become central to understanding the spread of alpha-synuclein pathology in MSA. Similar to the propagation of Aβ pathology in AD, alpha-synuclein aggregates may template the conversion of normal alpha-synuclein in recipient cells, allowing the pathology to spread throughout the nervous system [10].
Evidence for prion-like propagation in MSA includes:
The clinical features of SND in MSA-P include [11][12][13]:
The motor manifestations of MSA-P differ from Parkinson's disease in several important respects. Tremor is less prominent, while axial rigidity and postural instability are more severe and appear earlier. The response to levodopa is typically less robust and may not develop until higher doses are reached. Additionally, the progression of motor disability is more rapid in MSA-P compared to PD.
SND is associated with significant non-motor symptoms [14][15]:
Autonomic dysfunction is a core feature of MSA and often precedes motor symptoms. The combination of neurogenic orthostatic hypotension, urinary urgency/incontinence, and erectile dysfunction (in males) forms the autonomic triad that helps distinguish MSA from PD. REM sleep behavior disorder is also common and may precede the motor onset of MSA by years or decades.
Structural MRI in SND shows characteristic findings that aid in diagnosis [16][17]:
The "hot cross bun" sign is a characteristic MRI finding in MSA that reflects selective degeneration of pontocerebellar fibers, resulting in a cruciform pattern of T2 hyperintensity in the pons. While not specific to MSA, this finding supports the diagnosis when present and helps distinguish MSA from PD.
Functional imaging studies reveal more widespread abnormalities than would be expected from structural MRI alone. The pattern of hypometabolism on FDG-PET differs between MSA subtypes and can help guide clinical classification. Reduced dopamine transporter binding on DaT-SPECT confirms presynaptic dopaminergic degeneration but cannot reliably distinguish MSA from PD.
Multiple system atrophy has two major clinical subtypes [18][19]:
The severity of SND correlates with the degree of parkinsonism in MSA-P [4:1]. The subdivision between MSA-P and MSA-C is based on the predominant clinical features at presentation, with both subtypes showing some degree of mixed pathology as the disease progresses.
The distinguishing feature of MSA from Parkinson's disease is:
This oligodendroglial pathology is thought to be primary in MSA, with secondary neuronal degeneration. The concept of oligodendrogliopathy as the initiating event in MSA represents a fundamental shift from the neuron-centric view of PD and has important implications for therapeutic development.
The differentiation of MSA-P from PD is critical for prognostic counseling and therapeutic planning. Key distinguishing features include:
| Feature | MSA-P | Parkinson's Disease |
|---|---|---|
| Onset | Typically >50 years | Typically 50-70 years |
| Disease progression | Rapid (6-9 years) | Slow (15-20 years) |
| Tremor | Less common | Common |
| Response to levodopa | Poor or none | Good initially |
| Autonomic dysfunction | Early, severe | Variable, later |
| Pyramidal signs | Common | Uncommon |
Both MSA-P and progressive supranuclear palsy (PSP) are atypical parkinsonian disorders with distinct pathological substrates. PSP shows predominant involvement of the basal ganglia and brainstem, with characteristic supranuclear gaze palsy and early postural instability.
Current treatments for SND in MSA include [20]:
The response to dopaminergic therapy in MSA-P is typically less robust than in PD, with only approximately 30% of patients showing meaningful improvement with levodopa. This limited response likely reflects the severity of striatal degeneration and loss of postsynaptic dopamine receptors.
Multidisciplinary care is essential for optimizing quality of life in MSA patients. Physical therapy focusing on balance and gait training can help reduce fall risk, while speech therapy addresses the dysarthria and dysphagia that commonly develop as the disease progresses.
Several disease-modifying approaches are currently under investigation for MSA [21]. Immunotherapy targeting alpha-synuclein aims to reduce the burden of toxic alpha-synuclein species, while neuroprotective approaches focus on preserving neuronal function and promoting oligodendrocyte survival.
SND in MSA typically follows a more rapid course than Parkinson's disease [18:1]:
The prognosis for MSA is generally worse than for PD, reflecting the more widespread neuropathology and the involvement of autonomic pathways that regulate critical physiological functions.
While alpha-synuclein is the primary pathological protein in MSA, tau pathology is also frequently observed in affected brains [22]. The co-occurrence of tau and alpha-synuclein pathology may influence clinical presentation and disease progression, and understanding this relationship is important for developing comprehensive therapeutic strategies.
Current research efforts are focused on developing biomarkers that can aid in the early and accurate diagnosis of MSA. Promising approaches include:
The therapeutic pipeline for MSA includes:
Striatonigral degeneration represents the pathological substrate of parkinsonian symptoms in multiple system atrophy. The combination of oligodendroglial alpha-synuclein pathology, severe dopaminergic neuron loss, and striatal degeneration creates a distinctive clinical syndrome that differs from Parkinson's disease. Understanding the mechanisms of SND is essential for developing disease-modifying therapies targeting the underlying alpha-synucleinopathy.
The substantia nigra pars compacta (SNc) contains dopaminergic neurons that are selectively vulnerable in MSA[1:1]:
Both direct and indirect pathway neurons are affected in SND[2:2]:
| Pathway | Receptor | Effect of Dopamine | Effect in SND |
|---|---|---|---|
| Direct | D1 | Facilitates movement | Impaired |
| Indirect | D2 | Suppresses movement | Disinhibited |
Advanced imaging reveals characteristic patterns[16:1][17:1]:
The response to levodopa in MSA-P differs from PD[11:1][12:1]:
Novel approaches under investigation include[20:1]:
This section highlights recent publications relevant to this mechanism.
Ahmed Z, et al. "Glial cytoplasmic inclusions in MSA". 2011. ↩︎
Koga S, et al. "Neuropathology of multiple system atrophy". 2015. ↩︎ ↩︎
Jellinger KA. "Neuropathology of multiple system atrophy". 2014. ↩︎
Song YJ, et al. "Alpha-synuclein aggregation in oligodendrocytes". 2012. ↩︎
Halliday GM, et al. "The neurobiology of MSA". 2011. ↩︎
Prigione A, et al. "Exosomes in MSA pathogenesis". 2016. ↩︎
McDonald A, et al. "Clinical features of MSA-P". 2019. ↩︎ ↩︎
Bhatia KP, et al. "Current concepts in the diagnosis and management of MSA". 2018. ↩︎ ↩︎
Wenning GK, et al. "Multiple system atrophy: a review of 203 pathologically proven cases". 2013. ↩︎
Stamelou M, et al. "Motor and non-motor features in MSA". 2010. ↩︎
Kelley RE, et al. "Autonomic dysfunction in MSA". 2015. ↩︎
Ferman TJ, et al. "Diffusion MRI in atypical parkinsonian disorders". 2016. ↩︎ ↩︎
Ivanova MG, et al. "Neuroimaging findings in MSA". 2016. ↩︎ ↩︎
Kalia LV, Lang AE. "Multiple system atrophy". 2013. ↩︎ ↩︎
Gilman S, et al. "Second consensus statement on the diagnosis of MSA". 2008. ↩︎
Krismer F, et al. "Neuroprotective strategies in MSA". 2017. ↩︎ ↩︎
Valera E, et al. "Immunotherapy targeting alpha-synuclein in MSA". 2016. ↩︎
Kiyoshi Y, et al. "Tau pathology in MSA". 2016. ↩︎