Parkinson’s disease (PD) diagnosis is primarily clinical, relying on a comprehensive evaluation of an individual’s medical history, reported symptoms, and neurological examination. Currently, there isn’t a definitive laboratory test or imaging scan that can definitively diagnose PD. However, specific diagnostic tools like the Dopamine Transporter Scan (DaTscan), alongside Magnetic Resonance Imaging (MRI) of the brain and blood tests, play a crucial role in supporting a Parkinson’s diagnosis and excluding other conditions that may mimic PD.
Accurately diagnosing Parkinson’s, especially in its early stages, can present challenges. While initial diagnoses are often made by general practitioners or internists, seeking a consultation from a movement disorder specialist is frequently recommended. These specialists are neurologists who possess focused expertise and training in diagnosing and treating PD and related movement disorders. The most recent diagnostic criteria, established by the International Parkinson and Movement Disorder Society (MDS), represent the current understanding of PD and aid specialists in accurate diagnosis.
For a Parkinson’s disease diagnosis to be considered, bradykinesia (slowness of movement) must be present. Furthermore, at least one of the following symptoms must also be observed:
- Resting tremor: Shaking or tremor in a limb when it is at rest.
- Rigidity: Stiffness or rigidity of the limbs or trunk.
- Postural instability: Balance problems and increased risk of falls.
The Neurological Examination: Cornerstone of Parkinson’s Diagnosis
The initial and most vital step in diagnosing Parkinson’s disease involves a thorough medical history review and a physical examination conducted by a neurologist. This clinical assessment remains the gold standard for diagnosing PD.
During a neurology appointment, the diagnosis process includes:
- Detailed Medical History: The neurologist will gather an in-depth account of your symptoms, pre-existing medical conditions, current and past medications, family medical history, and lifestyle factors. It’s important to identify if any current medications or other medical conditions could be causing Parkinsonian symptoms.
- Comprehensive Neurological Examination: This examination involves the neurologist asking you to perform various tasks to evaluate:
- Facial Expression and Speech: Assessing if your expressions are animated and speech is clear.
- Tremor: Observing for tremors in your limbs while at rest and during activity.
- Rigidity: Checking for stiffness in your arms, legs, and neck.
- Gait and Balance: Evaluating your walking pattern, step length, turning ability, balance, and posture.
- Fine Motor Skills & Agility: Assessing the agility of your arms and legs through specific movements.
Neurologists often use the Unified Parkinson’s Disease Rating Scale (UPDRS) to systematically record findings during the examination. This standardized scale is used globally by neurologists and movement disorder specialists to comprehensively assess and document the condition of individuals with PD. The UPDRS serves as a baseline measurement, helps evaluate medication effectiveness, and track disease progression over time.
In Parkinson’s disease, the underlying issue is the degeneration of neurons that produce dopamine, a critical neurotransmitter. To manage symptoms, doctors often prescribe dopaminergic medications, which aim to replenish dopamine levels or enhance its effect in the brain. Typically, individuals with PD experience improvements in movement speed, stiffness, and tremor after starting these medications.
If a patient shows limited response to dopaminergic medication, it may prompt the neurologist to reconsider the diagnosis and conduct further investigations, such as brain MRI or lab tests, to explore alternative conditions. In cases where the PD diagnosis remains uncertain after the initial assessment, a DaTscan may be considered to provide further diagnostic clarity.
DaTscan: Visualizing Dopamine Transporters for Diagnostic Insight
The Dopamine Transporter Scan, or DaTscan, received FDA approval in 2011 as an advanced imaging technique to visualize the dopamine system within the brain. Unlike an MRI, which focuses on brain structure, a DaTscan assesses brain function, specifically the dopamine system. It can reveal if there is reduced function in the regions of the brain responsible for motor control, which is characteristic of Parkinson’s disease.
A DaTscan involves a simple procedure. A small amount of a radioactive tracer is injected into the bloodstream. This tracer binds to dopamine transporters, proteins on dopamine neurons. A Single-Photon Emission Computed Tomography (SPECT) scanner then detects the location and levels of the tracer in the brain. The resulting DaTscan image provides a visual representation of dopamine transporter availability, reflecting the health of dopamine neurons.
A normal DaTscan result typically suggests that dopamine function is intact, making Parkinson’s disease less likely. However, it’s important to note that a negative DaTscan doesn’t entirely rule out PD, particularly in the very early stages of the disease when dopamine loss might be minimal. Conversely, a positive DaTscan, indicating reduced dopamine transporter activity, can strongly support a Parkinson’s diagnosis. Crucially, a DaTscan can help differentiate Parkinson’s disease from essential tremor (ET), a different neurological condition that does not involve dopamine deficiency.
However, it’s important to understand the limitations of a DaTscan. While a positive DaTscan is supportive of Parkinsonian syndromes, it cannot distinguish PD from other atypical parkinsonian disorders that also involve dopamine loss, such as Progressive Supranuclear Palsy, Multiple System Atrophy, and Corticobasal Syndrome. Therefore, a positive DaTscan result alone is not sufficient to definitively diagnose Parkinson’s disease specifically.
Is a DaTscan Necessary for Everyone with Parkinsonian Symptoms?
In many instances, a DaTscan is not a mandatory requirement for diagnosing Parkinson’s disease. When an individual’s medical history and neurological examination findings are consistent with typical Parkinson’s and fulfill the established diagnostic criteria, a DaTscan is often unnecessary.
However, there are specific situations where a physician may recommend a DaTscan to aid in diagnosis. These include cases where:
- Symptoms are Mild or Atypical: If the signs and symptoms are subtle or don’t fully align with classic Parkinson’s presentation, a DaTscan can provide additional objective data to support or refine the diagnosis.
- Uncertainty in Diagnosis: In cases where the diagnosis remains unclear after the initial clinical evaluation, a DaTscan can help increase diagnostic confidence.
- Poor Response to Therapy: If a patient’s response to initial dopaminergic medications is not as expected, a DaTscan might be ordered to reassess the diagnosis and rule out other conditions.
It is essential to reiterate that the DaTscan is a supplementary diagnostic tool. The diagnosis of Parkinson’s disease fundamentally relies on a comprehensive clinical evaluation, including medical history and neurological examination. The DaTscan serves to enhance the diagnostic picture and is not intended as a standalone diagnostic test for Parkinson’s.
Figure 1 illustrates a DaTscan of a healthy brain, demonstrating normal dopamine transporter activity. In contrast, Figures 2 through 4 display abnormal DaTscans, indicating reduced dopamine transporter function consistent with neurodegeneration seen in Parkinsonian syndromes.
While generally safe, the DaTscan procedure can have potential side effects, although they are typically mild. Reported adverse reactions include headache, nausea, vertigo, dry mouth, and mild dizziness. Hypersensitivity reactions and injection site pain are less common. To minimize radiation exposure, patients are advised to hydrate well both before and after the DaTscan to promote frequent urination and eliminate the radioactive tracer from the body. Increased fluid intake and frequent urination are recommended for the first 48 hours following the DaTscan.
If you are considering a DaTscan, it is crucial to discuss it with your doctor to determine if it is appropriate for your individual situation. DaTscans are generally covered by Medicare and Medicaid, and most private insurers are also likely to cover the cost, although coverage policies can vary. It is always advisable to confirm coverage with your insurance provider prior to undergoing the procedure.
For further information, resources like “What’s Hot in PD? An Update on DaTscanning for Parkinson’s Disease Diagnosis” offer valuable insights into the role of DaTscans in Parkinson’s diagnosis.
Syn-One Test: Skin Biopsy as a Diagnostic Aid
The Syn-One Test® represents another diagnostic tool that can assist in confirming a Parkinson’s diagnosis. This pathological test utilizes skin biopsies to detect phosphorylated alpha-synuclein in nerve fibers. Alpha-synuclein is a protein closely associated with Parkinson’s disease, and its phosphorylated form is considered a hallmark of synucleinopathies, including PD.
The Syn-One Test procedure involves a neurologist or physician performing three small skin biopsies, typically from the upper back, lower thigh, and lower leg, after numbing the areas with a local anesthetic. The skin samples are then sent to a specialized lab for analysis. Results usually take approximately two to three weeks to be delivered to the ordering physician.
CND Life Sciences is the company that developed and processes the Syn-One Test. They report that Medicare generally covers the cost of the test when it is deemed medically necessary and appropriately ordered by a physician.
The Syn-One Test detects the presence of phosphorylated alpha-synuclein in skin nerve fibers. While the presence of this abnormal protein supports a diagnosis of a synucleinopathy, the test itself cannot differentiate between Parkinson’s disease, dementia with Lewy bodies, multiple system atrophy, or REM sleep behavior disorder, as all these conditions are associated with abnormal alpha-synuclein. Therefore, the Syn-One Test results must be interpreted in conjunction with other clinical findings and diagnostic evaluations to confirm a Parkinson’s diagnosis.
It’s important to note that the Syn-One Test, like the DaTscan, is not a standalone diagnostic test for Parkinson’s disease. PD diagnosis remains primarily clinical, based on neurological examination, response to dopaminergic therapies, and ongoing follow-up assessments. The Syn-One Test is most useful in cases where there is clinical uncertainty about whether a person has a synucleinopathy. In situations where a doctor decides to use a biomarker test to aid in confirming a Parkinson’s diagnosis, typically either a skin biopsy test (Syn-One) or a DaTscan is chosen, but not usually both. These tests serve similar purposes in providing supportive diagnostic information.
To learn more about the broader field of Parkinson’s biomarkers and their role in diagnosis and research, resources on Parkinson’s biomarkers offer further reading.
Parkinson’s Foundation Helpline
For any questions or concerns related to Parkinson’s disease diagnosis or management, the Parkinson’s Foundation Helpline is a valuable resource. You can contact specialists at 1-800-4PD-INFO (1-800-473-4636) or via email at [email protected]. The helpline provides support and information in English and Spanish, Monday through Friday, 9 a.m. to 7 p.m. ET.
Page reviewed by Dr. Michael S. Okun, Chair of Neurology and Executive Director at the Norman Fixel Institute for Neurological Diseases at the University of Florida Health and Dr. Lauren Fanty, Movement Disorders Fellow at the University of Florida, a Parkinson’s Foundation Center of Excellence.
References
- Postuma RB, et al. MDS clinical diagnostic criteria for Parkinson’s disease. J Mov Disord. 2015;30(12):1591-1599.
- Morbelli S, et al. EANM practice guideline/SNMMI procedure standard for dopaminergic imaging in Parkinsonian syndromes. Eur. J. Nucl. Med. Mol. Imaging. 2020;47:1885-1912.
- de la Fuente-Fernandez R. Role of DaTSCAN and clinical diagnosis in Parkinson disease. Neurology.2012;78:696-701.
