Parkinson’s disease diagnosis
Fact-checked by
There isn’t a specific Parkinson’s disease test that can conclusively diagnose the disease. Instead, diagnosing Parkinson’s is usually a complex, multistep process that involves reviewing a patient’s history, assessing symptoms, and medical tests.
Parkinson’s disease is caused by the death and dysfunction of cells in the brain that make the signaling molecule dopamine. Reduced dopamine signaling ultimately leads to the disease’s symptoms.
Parkinson’s is defined by four motor symptoms: slowed movement (bradykinesia), rigidity, tremor, and problems with balance and posture. To confirm a formal diagnosis of Parkinson’s, a person must have bradykinesia alongside at least one other motor symptom — usually rigidity and/or tremor, as balance problems tend to develop later in the disease.
Most patients also have nonmotor symptoms, such as depression, sleep problems, issues with cognition, and a reduced ability to smell. While testing for these issues isn’t a requirement for diagnosing Parkinson’s, identifying them can help trigger a suspicion of Parkinson’s and may be important for guiding care.
Most people with Parkinson’s won’t have every possible disease symptom and many Parkinson’s symptoms can be caused by other health problems. As such, a key part of diagnosing the disease is ruling out other possible explanations for a patient’s symptoms.
Getting tested
Establishing a diagnosis of Parkinson’s disease can be tricky, especially in the early stages of the disease. Typically a general practitioner or family physician is the first to suggest a possible diagnosis, but confirming a diagnosis usually requires a specialist such as a neurologist, who specializes in neurological disorders.
When Parkinson’s disease is suspected, clinicians will evaluate the patient’s medical history and perform a physical examination with motor tests to confirm whether the symptoms are consistent with Parkinson’s. Additional tests, such as evaluating a response to levodopa, a dopamine transporter scan, or testing for alpha-synuclein, can help to support the diagnosis, but usually aren’t required to confirm it.
Other assessments, like MRI, CT scan, and blood tests, can support a diagnosis and may help rule out other disorders that can cause similar symptoms.
Motor test
Since a Parkinson’s disease diagnosis is based primarily on whether a patient is having motor symptoms, tests to look for these motor symptoms are a key part of diagnosing the disease.
Bradykinesia, or slowed movement, must be present to confirm a Parkinson’s diagnosis. To test for bradykinesia, clinicians will often ask a patient to do a repetitive action, such as tapping the fingers, toes or heels, or opening and closing the fists, as fast as possible. People with bradykinesia generally have difficulty performing these tasks.
Along with bradykinesia, at least one other motor symptom must be present to confirm a formal Parkinson’s diagnosis.
Rigidity is usually tested by having a clinician apply force to try to bend a patient’s limb. With rigidity, the limb will not bend at all or will put up unusual amounts of resistance to it.
Tremor can sometimes be observed without any specific prompting, though clinicians may ask a patient to sit still in a particular position (for example, with hands rested on the knees) so the symptom is more easily visible. Clinicians also may have patients perform actions to see how the tremor changes. Most people with Parkinson’s have a resting tremor and shaking eases or disappears when the affected body parts are active.
Tests of balance may include having a patient perform activities like walking some distance or standing from a seated position. Clinicians also may gently pull at the patient’s shoulders to see if this throws him off balance.
Levodopa test
Levodopa and its derivatives are a class of medications widely considered to be the gold standard for Parkinson’s treatment. They work by giving the brain more raw material for making dopamine, thereby increasing its levels in the brain.
In a levodopa test, levodopa or a similar medication is administered at a high enough dose to show benefit in someone with Parkinson’s (low doses for a day or two aren’t reliable). Then, the patient and clinicians assess whether the treatment eased the symptoms.
Levodopa treatment usually causes symptoms to ease considerably in people with Parkinson’s disease, but it’s generally not effective in many other less prevalent conditions that can cause Parkinson’s-like symptoms. As such, testing a levodopa response in a person suspected of having Parkinson’s can help to determine if he has Parkinson’s disease or a distinct condition with similar symptoms.
Like any medication, levodopa can cause side effects. Common side effects associated with the levodopa test include:
- nausea and vomiting
- confusion or head fog
- sleepiness
- dizziness
- headache
- general feelings of weakness or discomfort.
Smell test
Loss of smell, also called olfactory dysfunction or hyposmia, is one of the most common nonmotor symptoms of Parkinson’s disease. People with Parkinson’s may have a notable loss of smell for years or even decades before other symptoms become apparent.
Testing for a loss of smell may be a useful for looking for early signs of Parkinson’s and it may help to distinguish between Parkinson’s and other conditions. The smell test is not very specific, however. Many people will have a loss of taste and smell as they age and not everyone who loses these senses will develop Parkinson’s.
The smell test usually has a person sniff and describe several predefined odors. For example, the widely used University of Pennsylvania smell identification test (UPSIT) is a “scratch and sniff” test made up of 40 microencapsulated odorants, where the person being tested must choose among four descriptors for each odorant.
Dopamine transporter scan
A dopamine transporter scan, or DaTscan, is basically a way to take a picture of the dopamine-making brain cells whose death and dysfunction causes Parkinson’s. DaTscan may help to differentiate between Parkinson’s and other conditions with similar symptoms, but it’s not usually required to reach a diagnosis; a review of symptoms is sufficient.
DaTscan is a form of single-photon emission computerized tomography (SPECT). During a DaTscan, a radioactive agent is injected into the patient’s bloodstream and is tracked using SPECT, a noninvasive scanner that can track the agent’s movement.
The agent used in DaTscan specifically sticks to a protein that dopamine-making cells use to transport dopamine into or out of the cell. Since the tracking agent sticks to these cells, they show up as brighter areas in the scan. In people with Parkinson’s disease, there are reduced levels of these cells in certain parts of the brain, especially the basal ganglia, a brain region central to controlling movement.
DaTscan is approved by the U.S. Food and Drug Administration to measure dopamine activity in adults with Parkinson’s, although the technology can’t reliably distinguish between Parkinson’s disease and other diseases that cause abnormal dopamine trafficking in the brain, such as progressive supranuclear palsy, corticobasal ganglionic degeneration, and multiple system atrophy.
Other imaging tests, such as MRI, functional MRI (fMRI), ultrasound of the brain, and positron emission tomography (PET) scans, may be conducted during a diagnostic workup for Parkinson’s disease. These techniques generally aren’t very helpful for diagnosing Parkinson’s, but they may be useful for ruling out other conditions.
Cognitive tests
People with Parkinson’s may have changes in their thinking abilities. Cognitive tests are used to assess thinking ability.
Common tests that check for problems with cognition include the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MOCA). A range of other assessments that measure specific aspects of cognition, such as memory, spatial reasoning, reaction time, or pattern recognition, also may help assess cognitive function.
Most people with Parkinson’s don’t have substantial cognitive issues by the time they’re diagnosed, although mild changes in cognition may be present. Testing for cognitive problems isn’t needed to confirm a diagnosis of Parkinson’s disease, but it can be invaluable for detecting issues early so patients and their families can get support to help manage living with Parkinson’s.
Testing for alpha-synuclein aggregates
A feature of Parkinson’s are aggregates, or clumps, of the protein alpha-synuclein in the brain. These clumps are toxic to nerves and are thought to play a central role in driving the disease.
Tests to detect these protein clumps are generally not necessary to confirm a diagnosis of Parkinson’s and they can’t distinguish between Parkinson’s and other disorders marked by alpha-synuclein clumping such as Lewy body dementia.
Still, tests of alpha-synuclein may help confirm a diagnosis if there is ambiguity based on other assessments. These tests also may be needed to determine eligibility for clinical trials, since some trials that test therapies that target alpha-synuclein are only open to people with confirmed aggregates of the protein.
Alpha-synuclein clumps can be detected from skin biopsies or by analyzing the cerebrospinal fluid, or CSF, that surrounds the brain. This last procedure is more invasive and technically arduous. It isn’t often used to help diagnose Parkinson’s outside of the context of research.
Genetic tests
Most cases of Parkinson’s don’t have any clear genetic cause, but about 5-10% of patients have a disease-linked mutation. These mutations are particularly common among people with a family history of the disease and may be linked to early-onset Parkinson’s.
Genetic testing can check if a person carries any Parkinson’s-related mutations. There are many different types of genetic tests, ranging from ones that look only for a few specific mutations to sequencing a patient’s entire genome.
This type of testing is not required to confirm a diagnosis of Parkinson’s disease and in most people with Parkinson’s, genetic testing won’t reveal any noteworthy results. But for people who carry a disease-related mutation, this information may help provide clues about their likely prognosis. As some experimental therapies are being developed to target specific Parkinson’s-related mutations, genetic testing may help determine eligibility for clinical trials.
Genetic testing can identify Parkinson’s-related mutations in people who don’t have Parkinson’s disease. In such cases, if a mutation is found, it can provide information about the person’s risk of developing Parkinson’s or passing the mutation on to future generations. It’s important to note that these tests are complicated to interpret, since some people who carry Parkinson’s-related mutations will never develop the disease.
Genetic counselors are professionals who specialize in interpreting genetic testing results and can help patients understand what genetic testing may mean for them.
Parkinson’s News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
FAQs about Parkinson's disease diagnosis
No test can confirm a diagnosis of Parkinson’s disease. Instead, a Parkinson’s diagnosis is established by a clinician examining a patient’s symptoms, especially his motor symptoms. Tests to look for common signs of Parkinson’s and to rule out other explanations for them aren’t required, but can help support a diagnosis.
Parkinson’s disease is typically diagnosed by a neurologist, who specializes in disorders that affect the brain and nervous system.
Typically a person will be evaluated for Parkinson’s disease if they are having symptoms that indicate the disorder, such as slowed movements, tremor, and/or rigidity.
To confirm a diagnosis of Parkinson’s disease, a patient must have bradykinesia (slowed movement) and at least one other motor symptom, such as tremor, rigidity, or problems with balance. The diagnosis can be made once these symptoms are established and other potential causes have been ruled out. Most people with Parkinson’s notice their first symptoms when they are 60 or older, but in about 10-20% of cases, Parkinson’s can be diagnosed before a person turns 50, where it’s called early-onset Parkinson’s.
Since diagnosing Parkinson’s requires testing for disease-typical symptoms and ruling out other possible causes for symptoms, confirming Parkinson’s usually takes some time. Studies suggest most people are diagnosed within the first six months after seeking medical attention for Parkinson’s-like symptoms, but it’s not uncommon to go up to about three years before a diagnosis is confirmed.
Related Articles
