Parkinson’s disease (PD) diagnosis is primarily clinical, relying on a neurologist’s evaluation of an individual’s medical history, symptoms, and physical examination. Unlike many conditions, there isn’t a definitive lab test to confirm PD. However, certain diagnostic tools, including brain MRI, blood tests, and a Dopamine Transporter Scan (DaTscan), can assist in supporting the diagnosis or ruling out other conditions mimicking Parkinson’s. This article will delve into the criteria and role of DaTscan, a type of SPECT scan, in the diagnosis process.
Accurate Parkinson’s diagnosis, especially in its early stages, can be challenging. While a general practitioner might initially suspect PD, consulting a movement disorder specialist is often recommended. These neurologists possess specialized expertise in diagnosing and treating PD and related movement disorders. The International Parkinson and Movement Disorder Society (MDS) has established the most current diagnostic criteria, reflecting the latest understanding of Parkinson’s disease.
According to these criteria, Bradykinesia, or slowness of movement, is essential for considering a Parkinson’s diagnosis. Furthermore, at least one of the following symptoms must also be present:
- Resting Tremor: Shaking or tremor in a limb when it is at rest.
- Rigidity: Stiffness in the arms, legs, or trunk.
- Postural Instability: Balance problems and increased falls.
The Neurological Examination: The Cornerstone of Diagnosis
A comprehensive neurological examination, combined with a detailed medical history, forms the foundation of Parkinson’s diagnosis. A neurologist will gather information on:
- Symptom History: Onset, progression, and nature of symptoms.
- Medical History: Pre-existing conditions, past illnesses, and surgical history.
- Medications: Current and past medications, as some can induce Parkinsonian symptoms.
- Family History: Whether Parkinson’s or similar conditions run in the family.
- Lifestyle Factors: Occupation, hobbies, and potential environmental exposures.
During the neurological exam, the neurologist will assess various motor skills and functions, observing:
- Facial Expression and Speech: Animation and clarity.
- Tremor: Presence and characteristics of tremor at rest and during action.
- Rigidity: Stiffness in limbs and neck.
- Gait and Balance: Walking pattern, step size, turning ability, and balance maintenance.
- Posture: Body alignment and stability.
Neurologists often use the Unified Parkinson’s Disease Rating Scale (UPDRS) to standardize and document exam findings. This scale serves as a baseline for tracking disease progression and medication effectiveness over time.
To further aid diagnosis and assess responsiveness, doctors may prescribe dopaminergic medications. These drugs aim to replenish dopamine levels in the brain, which are reduced in Parkinson’s disease. A positive response to these medications, such as improvement in movement speed, stiffness, or tremor, can support a PD diagnosis. Conversely, a lack of response might prompt further investigation and consideration of alternative diagnoses, potentially including MRI or lab work. In cases where the diagnosis remains uncertain, a DaTscan might be considered.
DaTscan: Visualizing the Dopamine System
A Dopamine Transporter Scan (DaTscan) is an FDA-approved imaging technique used since 2011 to visualize the dopamine system within the brain. Unlike MRI, which focuses on brain structure, DaTscan assesses brain function, specifically the dopamine system. It can reveal reduced function in brain regions crucial for motor control, which is characteristic of Parkinson’s.
DaTscan employs a small amount of a radioactive tracer injected into the patient. This tracer is then detected by a Single-Photon Emission Computed Tomography (SPECT) scanner. The SPECT scanner measures the concentration and distribution of the tracer, providing insights into dopamine transporter levels in the brain.
A negative DaTscan, indicating normal dopamine transporter function, suggests Parkinson’s is less likely. However, it’s important to note that a negative scan doesn’t entirely exclude PD, especially in the very early stages. Conversely, a positive DaTscan, showing reduced dopamine transporter function, strengthens the likelihood of Parkinson’s. DaTscan can also help differentiate PD from Essential Tremor (ET), as ET does not involve dopamine deficiency. However, DaTscan abnormalities are not exclusive to Parkinson’s; they can also be observed in atypical parkinsonism syndromes like Progressive Supranuclear Palsy, Multiple System Atrophy, and Corticobasal Syndrome. Thus, a positive DaTscan does not definitively distinguish Parkinson’s disease from these other conditions.
Determining the Need for a DaTscan
In many instances, a DaTscan is not necessary for diagnosing Parkinson’s disease. If a patient’s medical history and neurological examination strongly suggest PD and they meet the diagnostic criteria, a DaTscan is typically not required. However, a physician might recommend a DaTscan in situations where:
- Symptoms are mild or atypical.
- Diagnostic criteria are not fully met.
- Response to initial therapy is unsatisfactory or unclear.
It’s crucial to remember that DaTscan is a supplementary tool to aid diagnosis, not a standalone diagnostic test. The diagnosis of Parkinson’s remains primarily based on clinical evaluation. DaTscan serves to provide additional information and complete the diagnostic picture in uncertain cases.
Figure 1 shows a scan image of a healthy brain. By comparison, Figures 2 through 4 are examples of abnormal scans that could show brain degeneration, which is consistent with a diagnosis of Parkinsonian syndrome.
Potential side effects of DaTscan are generally mild and may include headache, nausea, vertigo, dry mouth, and dizziness. Hypersensitivity reactions and injection site pain are also possible but less common. To minimize radiation exposure, patients are advised to hydrate well before and after the scan to promote frequent urination and eliminate the radioactive tracer from the body.
Discuss with your doctor whether a DaTscan is appropriate for your individual situation. DaTscans are typically covered by Medicare and Medicaid, and most private insurers also provide coverage, although it’s advisable to confirm coverage details with your insurer beforehand.
Alternative Diagnostic Tools: The Syn-One Test
The Syn-One Test®, a pathological skin biopsy test, offers another approach to supporting Parkinson’s diagnosis. This test analyzes skin samples to detect phosphorylated alpha-synuclein in nerve fibers, a protein strongly linked to Parkinson’s.
For the Syn-One Test, a physician performs three small skin biopsies, usually from the upper back, lower thigh, and lower leg, after numbing the areas with local anesthetic. The results typically take two to three weeks. Medicare generally covers the cost of the Syn-One Test when appropriately ordered.
The presence of phosphorylated alpha-synuclein in skin nerve fibers can support a diagnosis of a synucleinopathy, but the Syn-One Test cannot differentiate between Parkinson’s disease, Dementia with Lewy Bodies, Multiple System Atrophy, or REM Sleep Behavior Disorder. It serves as one piece of information alongside other clinical findings.
It’s important to understand that neither the Syn-One Test nor the DaTscan alone diagnoses Parkinson’s disease. PD diagnosis relies on a combination of neurological examination, response to dopaminergic medication, and observation over multiple visits. In cases where diagnostic confirmation is needed, doctors usually choose either a DaTscan or a Syn-One Test, but typically not both, as they provide similar types of supportive diagnostic information.
For further information and support, the Parkinson’s Foundation Helpline is available at 1-800-4PD-INFO (1-800-473-4636) or [email protected].
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.
