Diagnosing Parkinson’s

How Parkinson’s Disease is Diagnosed

The approach to PD diagnosis is rapidly evolving. Recent advances in biomarker development—including new imaging techniques, skin biopsy tests, cerebrospinal fluid analysis, and emerging blood-based tests—are changing how PD is diagnosed and may allow for diagnosis at earlier stages than previously possible.

Understanding the Diagnostic Process

Seeing a Movement Disorder Specialist

What is a movement disorder specialist?

A movement disorder specialist is a physician who has undergone additional, subspecialty training in the diagnosis and treatment of movement disorders, such as Parkinson’s, after training in general neurology. This type of specialist is best suited to evaluate your symptoms and determine whether additional testing is necessary to help with diagnosis. Depending on where you live, there may not be a movement disorder specialist near you, in which case, you should seek the advice of a general neurologist.  

Learn more about movement disorder specialists

What to Expect During Your First Visit

When you or someone you know first visits a physician for the evaluation of potential Parkinson’s disease symptoms, it is helpful to know what to expect. During the first visit, the physician should take you through a series of physical tests and observations.

Parkinson’s Diagnosis Checklist:

• Take a complete and careful medical history
• Review your current medications to determine if any could contribute to parkinsonian symptoms
• Take your blood pressure while you sit and stand
• Assess your thinking (or cognitive) skills
• Examine your facial expression
• Look for tremor in your face, hands, arms, or legs
• Examine whether there is stiffness in your arms, legs, torso, or shoulders
• Determine whether you can get up easily from a chair, especially without using your arms
• Examine your walking pattern
• Assess your balance as you stand

Typically, a trained physician will only consider the diagnosis of Parkinson’s disease if the person being examined has at least two of the core motor symptoms of Parkinson’s, including tremor, the characteristic bradykinesia (slowness of movement), or rigidity.

At the end of your visit, the physician should discuss with you why you may or may not have Parkinson’s disease and the level of certainty about the diagnosis. This determination is based on your medical history and examination. Your physician should continue to re-evaluate your diagnosis at follow-up visits, as diagnosing Parkinson’s disease is not always straightforward and some symptoms may evolve over time.

When Additional Testing May Be Recommended by Your Doctor

For many people with classic Parkinson’s symptoms—such as unilateral (one-sided) tremor at rest, good response to levodopa medication, and no concerning features—a clinical diagnosis is sufficient and no additional testing is needed.

However in certain clinical situations your physician may recommend additional tests to confirm a diagnosis of Parkinson’s disease. For example, perhaps only one core motor symptom of Parkinson’s is present, or your tremor does not appear to be classically at rest, or your neurologic exam looks more complicated because of an additional medical problem. In these cases, a confirmatory test may be helpful. 

Sometimes certain “red flags” are present, such as frequent early falls, early cognitive changes, rapid progression, poor response to levodopa, or atypical symptoms. In these situations, the diagnosis may not be Parkinson’s disease, but rather an atypical parkinsonian syndromes. When these features exist, some of the current biomarkers can help with diagnosis, but others are positive for both PD and the atypical syndromes. In these situations, a movement disorders physician can help decide which if any additional testing can be helpful.

Diagnostic Testing Options for Parkinson’s

DaTscan: The Most Established Imaging Test

DaTscan is an FDA-approved imaging test that visualizes the dopamine system in the brain. A radioactive tracer is injected and attaches to dopamine transporters on dopamine neurons. Several hours later, special imaging equipment scans the head to detect the tracer’s presence.

When DaTscan is most helpful:

• Distinguishing essential tremor from Parkinson’s disease
• Uncertain early-stage cases when symptoms are subtle
• Determining if symptoms are caused by medications rather than Parkinson’s
• Cases where tremor is absent

Understanding results:

A DaTscan in someone with PD typically shows reduced signal in the striatum. A major 2024 study comparing DaTscan results to autopsy findings showed 100% sensitivity for Parkinson’s disease and 100% negative predictive value—meaning all confirmed PD cases had abnormal DaTscans, and normal DaTscans ruled out PD.

Important limitations:

While highly sensitive, DaTscan cannot distinguish between different parkinsonian disorders. An abnormal DaTscan can occur in PD, multiple system atrophy (MSA), progressive supranuclear palsy (PSP), corticobasal syndrome, and certain dementias.

Learn more about DaTscan

Biomarker Tests for Alpha-Synuclein

One hallmark of Parkinson’s disease is the accumulation of abnormal alpha-synuclein protein in brain cells. Scientists have developed tests that can detect this protein in more accessible tissues.

Skin Biopsy Test

The skin biopsy test detects abnormal alpha-synuclein deposits in peripheral nerves located in the skin. This test has gained more traction, following the publication of  a large NIH-funded study in 2024.

• How it works: Three small skin samples are taken in a doctor’s office (neck, thigh, and leg), sent to a laboratory, with results typically available within a month. The procedure is simple—local anesthetic numbs each site before a small punch tool removes a tiny skin sample.
• Accuracy: Based on the 2024 Syn-One study, the test has a positive predictive value of 93% for those with Parkinson’s disease and a 95.5% positive predictive value sensitive for detecting synucleinopathies in general (PD, Dementia with Lewy Bodies, or Multiple System Atrophy). It can be useful in distinguishing these conditions from other parkinsonian conditions like PSP which is characterized by abnormal tau protein and not abnormal phosphorylated alpha-synuclein.
• Important finding: Research revealed that approximately 60% of people with PD have small fiber neuropathy in their feet, explaining why many experience burning sensations—a symptom that can be treated with neuropathic pain medications.

Learn more about biomarker tests for PD

Cerebrospinal Fluid Test: Seed Amplification Assay

The seed amplification assay (SAA) detects abnormal alpha-synuclein in cerebrospinal fluid through a clever amplification technique—the abnormal protein acts as a “seed” that causes normal alpha-synuclein to misfold, making it easier to detect.

• Key findings from research: A large 2024 study found the test had a sensitivity of 87%, rising to 97% for patients with a decreased sense of smell (hyposmia). One result of the study that was particularly exciting was the detection of abnormal alpha-synuclein in pre-motor PD. About 93% of people with both REM sleep behavior disorder and hyposmia tested positive, even when their DaTscans were normal. This means that the SAA test could potentially be used to diagnose people with Parkinson’s disease prior to onset of motor symptoms.

Watch Dr. Saint Hilaire’s detailed discussion of diagnostic tests

Blood-Based Tests: The Future of Early Detection

A major research focus is developing blood tests that could diagnose Parkinson’s before motor symptoms appear. Blood tests are minimally invasive, relatively inexpensive, and could potentially be used for widespread screening. Blood tests for PD however, are still in the experimental stages.

Transfer RNA (tRNA) Fragment Blood Test:

In 2025, researchers published groundbreaking work on an RNA-based blood test that measures specific tRNA fragments. The test analyzes the ratio of two biomarkers—one elevated in PD patients, one reduced—to distinguish between late-stage PD, pre-symptomatic individuals at risk, and healthy controls, with 86% accuracy.

This blood test could be particularly valuable for people with pre-motor symptoms (REM behavior sleep disorder or smell loss) or those with family history or genetic mutations that increase PD risk. The FDA’s recent approval of a blood test for Alzheimer’s disease sets a precedent that may help fast-track similar PD diagnostics.

Current status: Undergoing further validation; not yet FDA-approved or commercially available.

Read more about blood-based diagnostic research | APDA-funded research

Other Brain Imaging and MRI Options

While DaTscan is the most established imaging test in the United States, several other technologies are being developed for diagnosing PD. Many are not yet FDA-approved for PD diagnosis or covered by insurance, though this may change as more data becomes available.

Promising imaging techniques include:

• PET Scans (FDG-PET, F-DOPA PET): Measure glucose metabolism or dopamine production; high accuracy but involve radiation
• Advanced MRI techniques (NM-MRI, nigrosome-1 imaging, QSM): Non-invasive options showing promise, with some routinely used in countries like Australia
• Transcranial Sonography: Low-cost ultrasound option; portable and quick but less specific
• Alpha-Synuclein PET: Still in research stages; could potentially provide early, definitive diagnosis

Combining methods: Using multiple imaging technologies together (such as F-DOPA + MRI or NM-MRI + QSM) can provide more complete diagnostic pictures and better distinguish PD from related disorders.

Learn more about advanced brain imaging options

Standard MRI: Magnetic resonance imaging examines brain structure and may be used to help rule out other conditions or identify features suggesting atypical parkinsonism.

Other Diagnostic Approaches

Determining Diagnosis Through Response to Medication

If a person’s symptoms and neurologic examination are only suggestive of Parkinson’s disease or if the diagnosis is otherwise in doubt, the physician may prescribe a medication intended for Parkinson’s disease in order to gauge the response. In the case of typical Parkinson’s disease, there is a positive, predictable response to Parkinson’s disease medication; in the case of some related Parkinsonian syndromes, the response to medication may not be particularly robust, or it may be absent entirely.

If It’s Not Parkinson’s Disease, What Else Could It Be?

There are several other conditions that might produce symptoms that can be mistaken for Parkinson’s disease. Here are some possibilities:

Medication side effects: Certain drugs can produce or exacerbate parkinsonian symptoms. Because of this, your doctor should carefully review all your medications to determine if any could contribute to PD-like symptoms.

Essential tremor: This is a relatively common and benign cause of tremor that is often confused with the tremor of Parkinson’s disease. A general neurologist or movement disorder specialist is the best physician to help differentiate between these two conditions.

Atypical parkinsonian syndromes: Several neurologic conditions have symptoms similar to Parkinson’s disease, but they are often managed differently and may not respond well to PD medication. These include:

• Progressive supranuclear palsy (PSP)
• Corticobasal syndrome (CBS)
• Multiple system atrophy (MSA)
• Dementia with Lewy bodies (DLB)

Some of the biomarker tests described above can help distinguish between these conditions, though they each have limitations in terms of specificity.

Important Reminders About Diagnosing Parkinson’s

The clinical examination remains essential. All diagnostic tests must be interpreted alongside your clinical presentation. Tests provide valuable information, but they don’t replace the expertise of a trained physician who evaluates your symptoms, notes how you respond to medication, and follows your progress over time.

Not everyone needs additional testing. For people with classic Parkinson’s symptoms and no red flags, a clinical diagnosis by an experienced physician is sufficient.

Each test has specific uses and limitations. Your physician will recommend tests based on what diagnostic questions need answering—for example, DaTscan for distinguishing essential tremor from PD, or skin biopsy for determining if it’s a synucleinopathy versus tauopathy.

Genetic factors matter. Certain genetic forms of PD (such as LRRK2-associated) may not involve alpha-synuclein, affecting synuclein-based test accuracy.

Diagnosis can evolve. Your physician should re-evaluate your diagnosis at follow-up visits, as how you respond to medication and how symptoms progress provide important diagnostic information.

Getting a second opinion is appropriate. If questions remain, seeking another neurologist’s or movement disorder specialist’s opinion is common practice.

Next Steps After Diagnosis

Remember: Only a general neurologist or movement disorder specialist can provide you with a reliable diagnosis of Parkinson’s disease. Once you or your loved one has a diagnosis of Parkinson’s disease, it is time to discuss treatment options with your physician.