Multiple system atrophy (MSA) is one of the hardest neurological conditions to diagnose, and there is no single test that confirms it during a person’s lifetime. Diagnosis relies on a combination of clinical symptoms, autonomic function tests, and brain imaging, with certainty increasing as the disease progresses. In fact, when researchers compare clinical diagnoses to autopsy findings, only about 62% of cases are confirmed, and even at a patient’s last clinical visit, the positive predictive value reaches only 80%.
Why MSA Is So Difficult to Identify
MSA shares many features with Parkinson’s disease, particularly in its early stages. Both can cause slowness of movement, stiffness, and tremor. The overlap is significant enough that many people with MSA are initially told they have Parkinson’s. At a first visit, the sensitivity of a clinical MSA diagnosis is just 56%, meaning nearly half of people who actually have MSA are missed on initial evaluation. Diagnostic accuracy improves over time as more characteristic features emerge, but the process often takes years.
The Movement Disorder Society now defines four levels of diagnostic certainty: neuropathologically established (confirmed at autopsy), clinically established, clinically probable, and possible prodromal MSA. That last category exists specifically to capture people in the earliest stages, when symptoms are present but don’t yet meet the threshold for a firmer diagnosis.
The Two Subtypes and Their Key Features
Doctors classify MSA into two subtypes based on which symptoms dominate. Parkinsonian-type MSA (MSA-P) looks most like Parkinson’s disease, with slowness, stiffness, tremor, and balance problems, but it also includes autonomic dysfunction like urinary difficulties, abnormal sweating, and digestive issues. Cerebellar-type MSA (MSA-C) centers on coordination and balance problems (ataxia), difficulty swallowing, slurred or quivering speech, and abnormal eye movements.
Both subtypes involve autonomic nervous system failure, which is one of the strongest clues that something other than standard Parkinson’s is going on. Recognizing which subtype fits helps guide the diagnostic workup and determines which additional tests are most useful.
Red Flags That Point Away From Parkinson’s
Beyond the core motor symptoms, certain warning signs raise suspicion that a patient has MSA rather than Parkinson’s disease. The European MSA Study Group developed a standardized checklist of these “red flags” after studying 57 patients with probable MSA-P and 116 with probable Parkinson’s. A poor response to levodopa (the standard Parkinson’s medication) is one of the most telling signs. Additional red flags include early falls, rapid progression of disability, the presence of cerebellar signs like ataxia, and prominent autonomic failure appearing early in the disease course.
The study group proposed that a combination of at least two out of six red flag categories, alongside the core features, strengthens the case for an MSA diagnosis considerably. No single red flag is definitive on its own, but the pattern matters.
Autonomic Function Testing
Because autonomic failure is a hallmark of MSA, formal testing of the autonomic nervous system plays a central role in diagnosis. The most common evaluation is a tilt-table test or active standing test to check for orthostatic hypotension, defined as a sustained drop in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg within three minutes of standing. For patients who already have high blood pressure while lying down, a drop of 30 mmHg may be a more appropriate threshold.
This kind of blood pressure instability, called neurogenic orthostatic hypotension, reflects damage to the nerves that normally keep blood pressure stable when you change position. In practical terms, it causes lightheadedness, dizziness, or fainting when standing up. While orthostatic hypotension occurs in other conditions, its combination with motor symptoms and other autonomic problems (like bladder dysfunction or temperature regulation issues) strongly suggests MSA.
Brain Imaging Findings
MRI of the brain can reveal structural changes that support an MSA diagnosis, though these findings are not always present early in the disease. In MSA-C, the most recognized MRI sign is the “hot cross bun” sign: a cross-shaped bright signal on a specific type of MRI sequence, visible in the pons (a structure in the brainstem). This pattern reflects the loss of certain nerve fiber pathways connecting the brainstem to the cerebellum. Fiber tract imaging in patients with this sign has confirmed decreased volume of the corticospinal tracts, transverse pontocerebellar fibers, and cerebellar structures compared to healthy individuals.
The hot cross bun sign is not exclusive to MSA, though. It has been reported in several other conditions, including various types of spinocerebellar ataxia, fragile X tremor ataxia syndrome, and even some rare infections and cancers affecting the brain. So while the sign adds supporting evidence, it cannot confirm MSA on its own. In MSA-P, MRI may show shrinkage of the putamen (a deep brain structure involved in movement) or a characteristic dark rim around it, though these findings can be subtle.
Sleep Studies and Bladder Testing
REM sleep behavior disorder (RBD), a condition where people physically act out their dreams during sleep, is extremely common in MSA. A meta-analysis pooling data from 598 subjects found that 79.9% of MSA patients have RBD confirmed by polysomnography (an overnight sleep study). During normal REM sleep, your muscles are essentially paralyzed. In RBD, that paralysis fails, leading to kicking, punching, shouting, or other movements during dreams. RBD serves as a red flag for synucleinopathies, the family of diseases that includes MSA and Parkinson’s, and patients with both MSA and RBD tend to develop the disease at a younger age and experience more severe symptoms.
Bladder dysfunction is another early and prominent feature. Urodynamic testing, which measures how well the bladder stores and empties urine, often reveals specific abnormalities in MSA. A post-void residual volume greater than 100 mL (the amount of urine left in the bladder after urinating) suggests incomplete bladder emptying, which is common. Detrusor sphincter dyssynergia, where the bladder muscle and the sphincter contract at the same time instead of working in coordination, is also frequently detected. These findings help distinguish MSA from Parkinson’s, where bladder problems tend to appear later and are usually less severe.
How Diagnosis Comes Together
No single test diagnoses MSA. Instead, neurologists build a case by layering clinical findings. The process typically starts with a detailed neurological examination, looking for the combination of motor symptoms (parkinsonian or cerebellar) and autonomic failure. From there, additional testing fills in the picture: autonomic function testing to document blood pressure instability, brain MRI to look for structural changes, sleep studies if RBD is suspected, and bladder testing if urinary symptoms are prominent.
The timeline matters too. MSA progresses faster than Parkinson’s disease, with most patients needing a wheelchair within several years of symptom onset. A poor or fading response to levodopa, combined with rapid functional decline, pushes the diagnosis further toward MSA. Because early-stage MSA can look nearly identical to Parkinson’s, many people receive a revised diagnosis only after the disease has progressed enough to reveal its full pattern.
Definitive confirmation still requires examination of brain tissue after death, which is why the highest diagnostic category remains “neuropathologically established.” For living patients, the best achievable certainty is “clinically established,” reserved for cases where autonomic failure and motor features are both well documented and alternative explanations have been ruled out.