Patients Ask: Is There a Test For Parkinson's Disease?

Obtaining an accurate diagnosis of Parkinson’s disease, particularly early in the disease continuum, is a difficult, yet crucial, component needed to provide effective treatment for Parkinson’s disease patients.

While there is no single test for Parkinson’s disease, there are several symptoms and diagnostic tools that can be used in combination to diagnose Parkinson’s disease. 

Below, we provide a high-level overview of how Parkinson’s disease is diagnosed, highlighting current clinical diagnostic criteria, available imaging tests, and the path toward early and accurate Parkinson’s disease diagnosis.

Is There a Test for Parkinson’s Disease?

Currently, there is no single test for Parkinson’s disease—no brain scan or lab test (e.g. blood, cerebrospinal fluid, and urine) can provide a definitive diagnosis of Parkinson’s disease. Instead, doctors diagnose Parkinson’s disease “clinically,” meaning a diagnosis is dependent on medical history, answers to certain questions, a physical examination, and the presence of specific physical symptoms.

Typically, the process for diagnosing Parkinson’s disease follows these general steps:

1. A physical examination and review of medical history
2. A review of current and past medications
3. A neurological examination (e.g. assessment of gait, balance, agility, and muscle tone)

Clinical diagnosis of Parkinson’s disease, or any disease for that matter, relies heavily on the doctor’s judgment and expertise. Oftentimes, the patient’s symptoms, along with the neurological examination, are sufficient for determining the correct diagnosis, particularly for patients in the later stages of the disease. However, doctors may suggest further testing, such as brain imaging, to rule out any conditions that mimic the symptoms of Parkinson’s disease (Parkinson’s syndrome). 

Clinical Diagnostic Criteria for Parkinson’s Disease

As we continue to see advancements in neuroscience, and researchers continue to deepen our understanding of Parkinson’s disease, clinical diagnostic criteria will continue to evolve to better support more accurate diagnosis. 

Currently, Parkinson’s disease is considered likely in patients who exhibit two or more of the four main symptoms of Parkinson’s disease:

• Bradykinesia (slowed movement): Slow initiation of voluntary movement with a progressive reduction in speed and amplitude of repetitive actions
• Shaking or resting tremor: A tremor, or slight shaking, of the hand, fingers, or chin while at rest
• Rigidity: Stiffness in the arms, legs, or trunk
• Postural instability: Difficulty with balance (not caused by primary visual, vestibular, cerebellar, or proprioceptive dysfunction)

Currently, for diagnosis, many doctors use the gold standard checklist created by the UK Parkinson’s Disease Society Brain Bank. However, recently, a new set of diagnostic criteria created by the International Parkinson and Movement Disorder Society has come into use. This also included the first-ever criteria for prodromal Parkinson’s disease.

Imaging Tests for Parkinson’s Disease

While no lab or imaging test can definitively diagnose Parkinson’s disease, several helpful imaging tools can be used to support Parkinson’s disease diagnosis. 

For example, while not approved by the FDA for Parkinson’s disease diagnosis, positron emission tomography (PET) scans are often used during the diagnostic process to rule out other conditions.

Individuals with Parkinson’s disease experience dopamine deficits in the striatum resulting from the destruction of dopaminergic (dopamine-producing) neurons located in the substantia nigra. A dopamine transporter scan (DaTscan), a specific single-photon emission computerized tomography (SPECT) scan, can be used to visualize the dopaminergic neurons. 

For this test, a radioactive tracer is injected into the bloodstream, where it then circulates around the body, making its way to the brain. The drug binds to dopamine transmitters in the brain, producing detailed pictures of the dopamine system in the brain. Not everyone with suspected Parkinson’s disease will require this test, but it can help distinguish between other functional movement disorders, such as essential tremor.

The Path Towards Early, Accurate Diagnosis of Parkinson’s Disease

Like Alzheimer’s disease and many other neurological diseases, Parkinson’s disease begins long before symptoms arise. The benefits of early diagnosis of such diseases are immense and not only affect patients and their families but also the wider society and research community. 

Research efforts surrounding Parkinson’s disease risk factors, early symptoms, traditional biomarkers, and digital biomarkers will pave the way for an earlier, more accurate diagnosis. Our growing understanding of the factors involved in Parkinson’s disease risk, development, and progression opens the door to more robust and sensitive testing and diagnostic approaches.