Multiple System Atrophy

Multiple system atrophy (MSA) is a rare, sporadic, adult-onset, progressive, and fatal neurodegenerative disease characterized by a variable combination of autonomic failure, parkinsonism, and cerebellar ataxia. The neuropathologic hallmark — accumulation of misfolded α-synuclein in oligodendrocytes (glial cytoplasmic inclusions, or GCIs) — fundamentally distinguishes MSA from all other synucleinopathies (PD, DLB, pure autonomic failure), where α-synuclein aggregates in neurons. This glial-versus-neuronal distinction has major implications for biomarker interpretation: the CSF α-synuclein seed amplification assay (SAA), now widely available for synucleinopathy confirmation, is typically negative in MSA — a finding that can be confusing but is diagnostically informative when understood in context. Early recognition of MSA prevents years of futile levodopa titration, guides autonomic management, avoids inappropriate DBS referral, and directs patients toward palliative care integration and emerging clinical trials.

Epidemiology and Pathology

Crude prevalence ranges from 0.5 to 17 per 100,000 depending on the population studied, with sex-specific prevalence estimated at 2.75 per 100,000 in men and 1.19 per 100,000 in women. Symptom onset typically occurs in the mid-fifties. No consistent environmental or genetic risk factors have been identified, though COQ2 variants have been implicated in East Asian cohorts.

The pathologic signature of MSA is the glial cytoplasmic inclusion (GCI) — oligodendroglial aggregates of phosphorylated α-synuclein with accompanying neurodegeneration in striatonigral or olivopontocerebellar systems. Definite MSA still requires neuropathologic demonstration of GCIs. The α-synuclein "strain" in MSA differs conformationally from that in PD/DLB, which explains the different seeding kinetics on SAA and potentially the different clinical phenotype.

Clinical Features

Motor Subtypes

Two motor subtypes are recognized: MSA-P (parkinsonian predominant) and MSA-C (cerebellar predominant). MSA-P predominates in Western populations; MSA-C is more common in East Asia. Over time, features of both subtypes often overlap. The motor subtype designation is based on the predominant motor phenotype at presentation.

Extrapyramidal Features (MSA-P)

Parkinsonism in MSA consists of bradykinesia with rigidity and tremor, but differs from PD in several important ways. The tremor is typically postural and action-type with jerky myoclonic features or polyminimyoclonus rather than the classic pill-rolling rest tremor of PD. Dysarthria, dysphagia, gait difficulty (shuffling, festination, freezing), postural instability, and loss of balance usually manifest within 3 years of motor onset — far earlier than in PD. Anterocollis is present in 42–43% of MSA patients (compared with only 5.5% in PD and 10.5% in PSP), making it a useful clinical clue. Other postural deformities include camptocormia (severe anterior spinal flexion), Pisa syndrome (severe lateral flexion), and limb contractures.

Levodopa response in MSA is characteristically poor, though up to 65% of pathologically confirmed MSA patients show some initial response, and two-thirds develop drug-induced dyskinesia or dystonia. The pattern of levodopa-induced craniocervical dystonia (lower facial risus sardonicus) without limb dyskinesia is highly characteristic of MSA and rarely seen in PD. Even patients who initially show no levodopa response may worsen after withdrawal, suggesting a mild symptomatic effect.

Cerebellar Features (MSA-C)

Cerebellar ataxia symptoms include gait ataxia, limb ataxia, scanning/dysarthric speech (cerebellar pattern), and cerebellar ocular motor dysfunction. Pyramidal signs — hyperreflexia, Babinski or Hoffmann signs, spasticity — frequently coexist, reflecting the multisystem nature of the disease.

Autonomic Failure

Autonomic dysfunction is a defining feature of MSA and often precedes motor symptoms by years. Patients may initially present to cardiologists (for orthostatic hypotension), urologists (for urogenital dysfunction), or primary care (for recurrent UTIs) before being referred to a movement disorder specialist.

Neurogenic orthostatic hypotension (nOH) is defined as a systolic BP decrease ≥20 mmHg or diastolic decrease ≥10 mmHg within 3 minutes of standing, without compensatory heart rate increase (<0.5 bpm per mmHg systolic drop). The coexistence of nOH with supine hypertension creates a particularly challenging management dilemma. The coat-hanger sign — pain in the suboccipital, paracervical, and shoulder regions in a coat-hanger distribution — is a clinical marker of orthostatic hypotension-related ischemia.

Urogenital dysfunction includes urinary retention (post-void residual >100 mL — a core diagnostic criterion), urgency, incontinence, and erectile dysfunction (especially in men <60 years). Benign prostatic hyperplasia must be excluded in men. Sexual dysfunction in women includes reduced lubrication and arousal.

Other autonomic features: constipation and gastroparesis (common but nonspecific), cold discolored hands and feet (Raynaud-like), anhidrosis (quantitative sudomotor axon reflex test with thermoregulatory sweat test can localize to preganglionic pathology in MSA), and thermoregulatory impairment.

Plasma norepinephrine levels are normal in MSA (preganglionic autonomic failure) versus low in pure autonomic failure (postganglionic) — a useful differentiating point.

Stridor and Respiratory Dysfunction

Nocturnal stridor — a strained, high-pitched inspiratory sound caused by laryngeal dysfunction with narrowing of the rima glottidis — occurs in one-third to two-thirds of MSA patients and is associated with respiratory failure and sudden death during sleep. Stridor may be recognized clinically, and laryngoscopy is suggested to exclude structural lesions. Drug-induced sleep endoscopy or video polysomnography may confirm the diagnosis when clinical suspicion exists.

Other Features

RBD is reported in up to 88% of MSA patients on polysomnography and may be a prodromal feature, appearing years before motor onset. Anosmia is uncommon in MSA (unlike PD and DLB) — preserved olfaction in a patient with parkinsonism should raise suspicion for MSA or PSP. Cognitive impairment is generally mild; dementia is an exclusion criterion for clinically established MSA. Hallucinations not induced by drugs are uncommon. Depression and pseudobulbar affect occur. Pain related to dystonia, spasticity, orthostatic hypotension (coat-hanger sign), and postural deformities is frequent and underrecognized.

Diagnostic Criteria

Two main diagnostic frameworks are used: the 2008 Second Consensus Criteria and the 2022 MDS Criteria. The MDS criteria represent a significant advance in enabling earlier diagnosis.

MDS Supportive Features

Motor: rapid progression within 3 years, moderate-severe postural instability within 3 years, craniocervical dystonia induced by levodopa (without limb dyskinesia), severe speech impairment within 3 years, severe dysphagia within 3 years, unexplained Babinski sign, jerky myoclonic tremor, postural deformities.

Non-motor: stridor, inspiratory sighs, cold discolored extremities, erectile dysfunction (in men <60 for Clinically Probable), pathologic laughter or crying.

MRI Markers (Required for Clinically Established MSA)

The hot cross bun sign — cruciform pontine T2 hyperintensity caused by selective neuronal loss with preserved corticospinal tracts — is characteristic but not pathognomonic (also seen in spinocerebellar ataxias). Advanced diffusion-weighted MRI techniques including fixel-based analysis and machine learning–aided differentiation are under active development.

Biomarkers

α-Synuclein SAA (CSF): Standard protocols detect neuronal α-synuclein seeds (Lewy body–type) with high sensitivity for PD and DLB but are typically negative in MSA. This reflects the different cellular localization (glial vs neuronal) and possibly different α-synuclein strain conformation. A negative SAA in a patient with parkinsonism and autonomic failure should raise suspicion for MSA rather than rule out synucleinopathy. MSA-specific SAA protocols targeting glial α-synuclein strains are under development.

α-Synuclein skin biopsy: Detects phosphorylated α-synuclein in cutaneous nerve fibers with >92% sensitivity for synucleinopathies. In MSA, deposits are found predominantly in somatosensory fiber terminals at distal sites, whereas in PD/DLB they localize to autonomic fibers at proximal sites. This differential distribution pattern may eventually serve as a non-invasive differentiating biomarker.

Neurofilament light chain (NfL): Markedly elevated in MSA (and PSP/CBS) compared with PD. Correlates with disease severity and progression rate. The combination of SAA-negative + elevated NfL has higher diagnostic value than either test alone for differentiating MSA from PD.

Cardiac MIBG scintigraphy: Typically normal in MSA (preganglionic sympathetic pathology), contrasting with reduced uptake in PD and DLB (postganglionic). This can help differentiate MSA from other synucleinopathies when available.

DaT-SPECT: Shows reduced dopamine transporter uptake in MSA-P but cannot differentiate from PD, DLB, or PSP. FDG-PET may show hypometabolism in putamen, brainstem, and cerebellum.

Management

No disease-modifying therapies exist. Management is entirely symptomatic, requiring a multidisciplinary, multisystem approach with quality of life as the primary goal.

Motor Symptom Management

Deep brain stimulation is not recommended for MSA. A small number of case reports describe palliation of specific symptoms (rare limb dyskinesia, tremor), but systematic evidence is lacking and outcomes are generally poor.

Autonomic Failure Management

Other Symptom Management

RBD: Melatonin is first-line; clonazepam second-line (caution: may aggravate stridor, sleep apnea, daytime ataxia). Combination may be needed.

Stridor: CPAP and tracheostomy are the main options. Tracheostomy may prolong survival compared with CPAP or no treatment, and tracheostomy with mechanical ventilation may significantly extend survival further. Insufficient evidence supports botulinum toxin to vocal folds or minimally invasive vocal cord surgery.

Depression: SSRIs and SNRIs are preferred. Fluoxetine improved emotional and social quality of life in a randomized placebo-controlled trial in MSA.

Pain: Botulinum toxin for dystonia-related pain. Duloxetine, gabapentin, or pregabalin for neuropathic-type pain.

Palliative Care

Palliative care should be integrated early in the disease course — not reserved for end-of-life. It has demonstrated benefits in PD and atypical parkinsonism. Early neuropalliative care consultation optimizes symptom management (especially non-motor symptoms), facilitates advance care planning, addresses caregiver burden, and supports grief. A 2021 survey of atypical parkinsonism patients showed preference for disease and prognosis discussions at diagnosis, with end-of-life care discussions deferred until progression — highlighting the importance of patient-centered timing of these conversations.

Disease-Modification Trials

Over 30 compounds have been tested in MSA clinical trials targeting α-synuclein expression/aggregation/clearance, neuroinflammation, immunotherapy, mitochondrial dysfunction, and neurotrophic support. All have failed to demonstrate clinically meaningful disease modification.

The disconnect between positive preclinical data and negative clinical trials highlights the need for better understanding of disease mechanisms, improved preclinical models, refined clinical outcome measures, and validated biomarkers for patient selection and treatment monitoring. MSA's rapid progression makes it an attractive proof-of-concept target for disease modification, but the rarity of the condition (requiring multisite international collaboration) and diagnostic delay remain major barriers.

Prognosis

MSA is invariably fatal. Median survival from symptom onset is 6–10 years. Factors associated with shorter survival include older age at onset, early autonomic failure, early dysphagia, and stridor. Death commonly results from respiratory failure (stridor, aspiration pneumonia), cardiovascular complications of autonomic failure, or general debility. The most common cause of sudden death is nocturnal stridor with respiratory arrest.

References

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