The process of diagnosis for someone dealing with symptoms of Parkinson’s disease can sometimes leave the patient and even their healthcare provider frustrated due to the slow pace of assessment and multiple tests required to confidently confirm the presence of the disease. Most commonly, a neurologist will look for specific physical examination findings that are classic to Parkinson’s disease, like resting tremor or rigidity.
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However, symptoms or signs of Parkinson’s disease may not be obvious. For example, the types of tremors present may be mixed and suggest differing diagnoses. In inconclusive cases like these, the healthcare provider may recommend the use of an imaging drug, called DaTscan, and a single-positron emission computed tomography (SPECT) scan to capture images of the brain. Read more to learn about DaTscan, cases in which it may be prescribed, and the process for undergoing a SPECT scan to diagnose Parkinson's disease.
What Is a DaTscan?
A DaTscan is an imaging drug, also called Ioflupane I 123 or phenyltropane, that acts as a radioactive tracer for dopamine transporters within the brain. This drug was approved by the FDA in 2011. It may help distinguish the diagnosis of essential tremor from Parkinson's syndromes, like Parkinson’s disease or Parkinson’s disease dementia.
The drug is administered during the SPECT scan. This scanning technique gathers images of a particular area in the brain called the striatum, a cluster of neurons (nerve cells) in the subcortical basal ganglia of the forebrain. The striatum helps facilitate the transportation of dopamine.
What Is a SPECT Scan?
DaTscan is injected into the patient’s bloodstream and eventually circulates to the brain. The tracer attaches itself to a molecule found on dopamine neurons in the striatum called the dopamine transporter (or DAT). The patient then undergoes a SPECT scan which will produce an image of the dopaminergic neuron terminals that remain available in the striatum.
In patients with a diagnosis of Parkinson’s disease, or parkinsonism (referring more generally to a condition that causes symptoms that affect movement the way Parkinson's can), this area of the brain will show “dark.” This indicates the loss of dopamine-containing nerve cells within the brain, a hallmark of the disease.
Unlike other imaging tests, DaTscan with SPECT imaging assesses the function of the brain, rather than its anatomy or structure. In most imaging techniques used to visualize the brain, such as a computerized tomagraphy (CT) scan or a magnetic resonance imaging (MRI), patients with Parkinson’s disease who have not experienced a stroke or tumor will have normal scans. However, DaTscan and SPECT specifically visualize to what capacity dopamine is being utilized in the brain.
Purpose of Testing
In standard clinical diagnosis of Parkinson’s disease, a neurologist will look for four cardinal clinical symptoms:
- Bradykinesia (slowed movements)
- Tremor (so called "pill-rolling," occurring at rest)
- Rigidity (stiffness)
- Postural instability (stooped posture with shuffling gait and risk of falls)
Once it is determined that someone has these motor symptoms that are typical of Parkinson's disease, the healthcare provider will likely prescribe a dopaminergic therapy. These medications--such as carbidopa-levodopa, ropinirole, pramipexole, or rotigotine--treat the loss of dopamine. A positive response to the therapy is a sign of the proper diagnosis.
However, these neurological exam findings can sometimes be unclear. For example, some people may also experience essential tremor, which are tremors that occur during movement. In contrast, the tremor associated with Parkinson’s disease tends to be slower, may appear like someone is rolling a pill in their cupped hand, and notably occurs at rest. The DaTscan may be of benefit in situations like these when symptoms overlap.
A healthcare provider may also recommend a DaTscan to a patient who is interested in more intensive treatment options for Parkinson’s disease, like the placement of a deep brain stimulator (DBS), or other interventions.
Several studies have shown that the use of DaTscan has similar accuracy to a solely clinical diagnosis in cases of early Parkinson’s disease. Research also suggests an overall increase in confidence in the diagnosis among doctors, which also impacted clinical management for about 58% of their patients.
Risks and Contraindications
The most common side effects associated with the use of DaTscan include the following:
- Dizziness
- Headache
- Dry mouth
- Hunger
- Feeling of crawling skin
- Itching
- Rash
The potential side effects from DaTscan tend to be minimal and are relieved shortly after the test concludes. There is also a risk related to the radiation exposure in the SPECT scan, however, it too is minimal. DaTscan is administered through an injection, so there is a theoretical risk of a more serious infection, or even an allergic reaction, at the site of injection.
DaTscan and SPECT are not recommended for those with hypersensitivities or allergies to iodine. DaTscan is also not a good option for people with reduced kidney or liver function. Pregnant or nursing women are cautioned, as the effects are unknown and have not been evaluated in a research study, but these populations would be at low risk for Parkinson's disease anyhow.
Before the Test
If a DaTscan is the appropriate test for you, your healthcare provider will prescribe it at their discretion. The DaTscan injection and accompanying SPECT scan will usually take place in the nuclear medicine, or radiology, department of a hospital or in an outpatient clinic.
Days prior to this testing, your healthcare provider may ask you to stop taking certain medications that might interfere with the DaTscan results. Typically, medications used as dopaminergic therapies can continue to be used. However, specific dopaminergic stimulants that act on the central nervous system may interfere with DaTscan and should be stopped.
Your healthcare provider may also ask you to increase your intake of fluids 48 hours prior to testing to help protect the kidneys from the tracer. It will also best to remove all metallic jewelry before the scan.
During the Test
At least one hour before administering the DaTscan, the healthcare provider will give you a medication that will decrease the amount of radioactive iodine from the DaTscan that will go to your thyroid gland. The DaTscan will then be injected into your bloodstream.
You will likely be asked to lie quietly on your back for about 20 minutes during the SPECT scan. The SPECT machine is large and circular and will capture the scans of your brain from above you while rotating around your head.
After the Test
The DaTscan is typically an outpatient procedure, so you will likely be free to go home afterward.
Following the DaTsan, your healthcare provider may ask you to continue to increase your intake of liquids to frequently empty your bladder for the first 48 hours post-scan in order to flush out and release any remaining tracer. This will naturally be broken down by your body without any persistent effects.
Interpreting Results
Your healthcare provider, or a specialized neuro-radiologist or nuclear medicine specialist, will assess the images from the SPECT scan. In abnormal scans, the striatum will appear darker, indicating the loss of dopamine neurons, a signature of Parkinson’s disease.
While this assessment serves as an alternative diagnostic test for those with atypical symptoms, the use of DaTscan unfortunately comes with several limitations:
- DaTscans are unable to distinguish Parkinson’s disease from other neurodegenerative parkinsonian disorders or other diagnoses that impact dopamine levels, such as progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD).
- DaTscans are not currently used as preliminary tests to screen for Parkinson’s disease, and can only be used after classic motor symptoms are already present.
- The test is not currently used to indicate disease progression or to provide additional information that would clarify the anticipated response to dopaminergic therapies.
- DaTscans do not yield any quantitative findings and SPECT scans can only be assessed by eye. The scan can be misread, leading to an incorrect diagnosis.
Despite limitations, several studies are uncovering potential roles and benefits for using this test. Research suggests that in the future the use of DaTscan early in disease diagnosis, prior to dopamine therapy treatments, may be both cost-effective and provide helpful information for inconclusive symptoms related to Parkinson’s disease.
Preliminary studies have shown possible benefits in using DaTscan as a screening tool in patients with pre-symptomatic Parkinson’s disease or in those with early, strictly hemi-parkinsonian findings (symptoms affecting one side), but further research is required to determine the criteria for this screening. There is not yet a reliable way to determine what populations are at risk for Parkinson's disease and who could benefit from a DaTscan as a screening method.
Current research continues to investigate the use of DaTscan and SPECT scans as secondary screening methods for people at risk for developing Parkinson’s disease and as a method of monitoring disease progression and striatal dopaminergic dysfunction in patients being treated for Parkinson’s disease.
A Word From Verywell
In certain cases, symptoms or signs of Parkinson’s disease can be confusing for both the patient and the healthcare provider, resulting in uncertainty of the proper diagnosis. DaTscan used during SPECT scanning may be a good alternative to help alleviate this confusion. Keep in mind that like in any medical test, DaTscans can result in false positives and false negatives. However, DaTscan has the potential to direct both you and your healthcare provider in the right direction, optimizing the selection of treatment options. If you believe DaTscan may be a good option for you, chat with your practitioner to discuss the clinical context and necessity of the test for you.
