There is no specific test for Parkinson’s disease. This can make it hard for doctors to diagnose, especially in the early stages. How they test for Parkinson’s disease can depend on a person’s symptoms, but may include scans and other tests.

The symptoms of Parkinson’s disease mainly result from changes in dopamine activity in the brain. Tremors are a hallmark symptom, but other early symptoms include a loss of the sense of smell.

The symptoms can overlap with those of other conditions, such as Lewy body dementia and some types of stroke. Lewy body dementia can also occur with Parkinson’s disease.

Some antipsychotic medications can cause Parkinsonism. The symptoms of this are similar to those of Parkinson’s disease, but the diagnosis is different.

Getting an accurate diagnosis can help improve the outlook, as receiving early treatment can improve a person’s quality of life. Some drugs may help slow or prevent some changes.

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There is no specific test for diagnosing Parkinson’s disease. A doctor may diagnose it only by considering the symptoms.

If a person seeks medical advice for the following symptoms, the doctor may carry out tests to see if they have Parkinson’s disease:

  • shaking or tremors during rest
  • slow movements
  • muscle stiffness and rigidity
  • problems with balance and coordination, possibly leading to falls
  • a loss of the sense of smell
  • sleep problems, especially REM sleep behavior disorder or restless legs syndrome

The doctor will usually start by asking the person about their symptoms, how they feel, and how and when the symptoms started.

They will also carry out a physical examination, look at the individual’s medical history, and recommend some tests to rule out other conditions.

The doctor will ask about:

  • any existing conditions the person has
  • any drugs they are currently taking
  • whether or not they have had exposure to environmental toxins
  • whether or not any close family members have or have had Parkinson’s
  • whether or not they have any known genetic factors that might increase their risk

The early symptoms can resemble those of other conditions.

If a doctor believes that the person may have Parkinson’s disease, they may refer them to a neurologist or movement disorder specialist.

The specialist will evaluate the person’s motor function (movement). They will consider:

  • walking and gait
  • coordination and balance
  • some simple hand tasks
  • the agility of the legs and arms
  • muscle tone

The specialist may also check the person’s sense of smell and ask about pain.

They may prescribe a medication such as levodopa, which increases dopamine levels in the brain. If the person’s symptoms improve with this medication, it may indicate that Parkinson’s disease is present.

The following tests may help diagnose Parkinson’s disease:

Dopamine transporter scans

When a person has a dopamine transporter scan, a doctor will give them a small amount of a radioactive drug. Then, the doctor will scan the brain to check for activity in dopamine-producing cells.

The scan cannot diagnose Parkinson’s disease, but it may help support the doctor’s diagnosis.

It is important to note that the person may have a negative result and still have Parkinson’s disease. A positive result could also indicate another, similar condition, such as multiple system atrophy.

This is not a common test. Medicare and Medicaid will usually cover the cost of a scan, but the person should check with their insurance provider first.

Tests to rule out other conditions

Blood tests can help rule out other possible causes of the symptoms, such as abnormal thyroid hormone levels or liver damage.

An MRI or CT scan can check for signs of a stroke or brain tumor, which may cause similar symptoms.

Hydrocephalus (increased fluid in the brain) due to atrophy can occur with some types of dementia and would be visible with one of these imaging tests. If the person has neurologic symptoms but a normal scan result, Parkinson’s disease may be present.

The doctor may suggest a lumbar puncture to rule out inflammation or a brain infection.

Future testing options

Some experts are investigating blood tests to help distinguish Parkinson’s disease from other Parkinson’s-related conditions. However, these tests are not yet available.

People with Parkinson’s disease often have patchy areas on the skin that are dry and flaky. Some researchers have noted that Parkinson’s disease can also cause unusual sweating, bullous pemphigoid (blistering ulcers on the skin), and other skin changes. Because of this, they have proposed a skin biopsy as a future diagnostic tool.

A doctor will usually start by checking to see if two of the four main symptoms are present. These four main symptoms are:

  • tremors or shaking
  • slow movements
  • rigidity or stiffness in the arms, legs, or trunk
  • problems with balance

They will also consider whether or not the following statements are true:

  • The symptoms started on one side of the body.
  • Tremors are more evident at rest.
  • Scans and tests rule out other causes.
  • The symptoms improve with medications such as levodopa.

The doctor may need to observe the person for some time before deciding that their symptoms are consistently present and ruling out other possible causes.

In 2016, experts developed new criteria for diagnosing early stage (prodromal) Parkinson’s disease. They called these criteria the United Parkinson’s Disease Rating Scale.

These criteria involve:

1. Assessing the probability that the diagnosis will be Parkinson’s disease: For example, the doctor might start by considering the person’s age.

2. Assessing the variables: These include the following:

  • their walking speed
  • their scores on the Hoehn and Yahr scale
  • their sex
  • any environmental risks, such as smoking or caffeine use
  • genetic factors, such as family history or genetic test results
  • early signs and symptoms, such as a loss of the sense of smell and changes in movement
  • the results of scans and other diagnostic tests

3. Calculating the results: The doctor multiplies the factors and compares the result with a threshold measure.

Scores indicating that Parkinson’s disease is likely range from 75% to 99.7%.

A person with a result of 75% may have less specific symptoms that may or may not relate to Parkinson’s disease, such as constipation and depression. If the score is 80%, the doctor might diagnose the earliest stage of Parkinson’s.

They will enter the results of the medical examination into a table, which can help track and predict an individual’s progression through the stages of Parkinson’s disease. This takes into account a range of factors, including:

  • mood
  • thinking
  • daily living
  • tremors
  • complications arising from treatment
  • movement changes

It also means that doctors can compare data entered with future follow-up examinations or communicate data with other neurologists.

As the condition progresses, the symptoms will become more severe. A doctor may use stages to talk about the progression.

In stage 1, a person will have slight changes in posture, gait, and facial expression. They will be able to do most regular activities.

In stage 2, tremors will affect both sides of the body and be more noticeable. Daily tasks may become more challenging.

In stage 3, there may be problems with balance and coordination. Falls may be more likely, and the person may need help dressing.

In stage 4, the person may need full-time care. It may be difficult for them to walk without support.

In stage 5, the person’s mobility will be severely reduced. They may also experience confusion and hallucinations, which are side effects of some Parkinson’s disease medications.

Most medications help manage the symptoms effectively for 3–6 years. After this, however, the condition can be harder to treat.

Learn more about the stages of Parkinson’s disease here.

Receiving a diagnosis of Parkinson’s disease can be a life changing event for an individual and their loved ones. Having support from doctors, friends, and family will be important.

It can help to find out as much information as possible about:

  • what to expect
  • what the treatment options are
  • what kind of support is available
  • what kind of treatment one’s insurance will cover

It may also be helpful to join a local or online community group for people with Parkinson’s disease and their loved ones. A doctor will be able to advise on this.

National disease-specific organizations, such as the Parkinson’s Foundation, can also offer advice and information.