The journey to a Parkinson's disease diagnosis can be lengthy and uncertain, especially when a person has other chronic (long-term) conditions or is taking medications that may complicate identifying the source of motor symptoms. To make an accurate diagnosis, physicians rely on understanding how symptoms evolve over time and in what order and by ruling out other possible causes

A neurologist, particularly one specializing in movement disorders, often plays a key role in this process. Receiving a diagnosis from such a specialist can help reduce the risk of misdiagnosis.

How Is Parkinson’s Diagnosed?

Parkinson’s disease and other forms of parkinsonism result from the gradual loss of dopamine-producing neurons in the brain. Dopamine, a neurotransmitter (chemical messenger), is essential for transmitting signals between nerve cells, which helps regulate movement, motivation, reward, and mood. When dopamine levels drop, communication between the brain regions that control movement becomes disrupted. This can lead to symptoms including:

• Bradykinesia (slowed movements)
• Tremors
• Loss of balance
• Stiffness

Parkinson’s disease is the most common type of parkinsonism, accounting for around 80 percent of cases. Read more about types of parkinsonism.

Diagnosing parkinsonism is the first step, which requires the presence of bradykinesia along with either rest tremor (tremor when muscles are relaxed) or muscle rigidity. After confirming parkinsonism, a neurologist evaluates whether Parkinson’s disease is the likely cause.

Factors that suggest a Parkinson’s disease diagnosis include:

• Significant symptom improvement with dopaminergic medications like levodopa/carbidopa, where higher doses yield more noticeable benefits
• The occurrence of dyskinesia (involuntary movements such as writhing or head bobbing) as a side effect of levodopa/carbidopa

Factors that may suggest other conditions include:

• Motor symptoms that appear equally on both sides of the body
• Rapidly worsening walking difficulties that result in needing a wheelchair within five years
• Symptoms that do not significantly progress over five years in those not on medication
• Challenges with swallowing, speaking, or breathing that develop within five years
• Urinary issues emerging within five years

Other considerations that might lead a neurologist to explore different diagnoses include:

• Recent use of medications known to cause motor symptoms
• Motor symptoms that are limited to the legs for more than three years
• Lack of response to high doses of levodopa/carbidopa for moderate symptoms
• Brain scans that show normal dopamine-related function
• Presence of certain eye movement issues, aphasia (loss of ability to speak or understand speech), or another condition that could explain motor symptoms

Given these various factors, it may take time for a doctor to confirm a Parkinson’s diagnosis, as they need to observe how symptoms respond to medications and evolve over time.

Tests and What They Show

Various tests can support a Parkinson’s diagnosis or help rule out other conditions.

Medical History

The doctor will take a thorough history, asking about symptoms over time, family medical history, previous head traumas, any medications you take, and possible exposures to toxins. This comprehensive history can reveal risk factors that either increase suspicion of Parkinson’s or suggest other diagnoses.

Neurological Exam

A neurological exam assesses mental function, mood, and physical signs like muscle strength, reflexes, and coordination. The doctor may ask you to perform movements to assess slowness, rigidity, or balance. They might also check your ability to feel sensations by using tools like a tuning fork or testing hot and cold items on different parts of your body.

You may be asked to sniff strongly scented materials and asked to identify the odors. Loss of the sense of smell is a very common early symptom in people with Parkinson’s and may begin years before motor symptoms.

Dopaminergic Therapy

Since Parkinson’s disease responds better to certain medications, the neurologist is likely to prescribe levodopa/carbidopa to find out whether it helps your symptoms. The neurologist may inject you with the drug at the office and observe changes to your symptoms while you wait. They may also prescribe a longer course of oral levodopa/carbidopa for two months or more and ask you to report whether and how symptoms change. If symptoms improve, it suggests Parkinson’s is more likely.

DaTscan

DaTscan, an imaging method approved by the U.S. Food and Drug Administration (FDA), can help neurologists visualize dopamine-producing cells in the brain. DaTscan can help differentiate parkinsonism from essential tremor. DaTscan involves an intravenous (IV) injection of a radioactive tracer into the bloodstream that binds to dopamine-producing cells, allowing a special camera to detect abnormal dopamine function.

Although DaTscan is not definitive for diagnosing Parkinson’s, it can support the diagnosis. Potential side effects include:

• Headache
• Nausea
• Dizziness
• Dry mouth
• Sensation of skin crawling

Imaging Scans

If a Parkinson’s diagnosis is in question, a neurologist may order an imaging scan to check for problems with the structure of the brain. Imaging scans sometimes used include magnetic resonance imaging (MRI), functional MRI (fMRI), or positron emission tomography (PET).

Blood Tests

Around 10 percent to 15 percent of Parkinson’s cases are thought to be directly caused by a genetic mutation (variation) inherited from parents. If the doctor suspects a genetic form of Parkinson’s, especially in early-onset cases, they may order blood tests to check for specific genetic markers. Blood tests can also be used to rule out other conditions that might mimic Parkinson’s, like certain thyroid or metabolic disorders.

Ruling Out Other Conditions

The process of ruling out similar conditions is known as differential diagnosis. Parkinson’s has symptoms in common with conditions including Alzheimer’s disease, frontotemporal dementia, and Huntington’s disease. Certain medications, such as antipsychotics, can also cause symptoms similar to those of Parkinson’s disease, a form known as drug-induced parkinsonism.

Other conditions that may cause parkinsonism include:

• Secondary parkinsonism — Caused by brain injuries or illnesses, such as hydrocephalus (fluid buildup in the brain), some brain tumors, or stroke
• Wilson’s disease — A genetic disorder that causes copper buildup in the liver, brain, and other organs
• Metabolic and endocrine issues — Problems with the parathyroid gland, chronic liver disease, or abnormal calcium levels that sometimes mimic Parkinson’s symptoms
• Infections — Conditions like HIV, neurosyphilis, or progressive multifocal leukoencephalopathy (PML) that cause similar symptoms to those of Parkinson’s

A doctor might quickly rule out some conditions based on your medical history and simple blood tests. Others may require more time and repeat testing to confirm or exclude. Coexisting conditions can complicate the diagnosis, potentially leading to multiple diagnoses over time.

Find Your Team

MyParkinsonsTeam is the social network for people with Parkinson’s disease and their loved ones. On MyParkinsonsTeam, more than 105,000 members come together to ask questions, give advice, and share their stories with others who understand life with Parkinson’s disease.

Have you or a loved one been diagnosed with Parkinson’s disease? What was the diagnosis process like? Share your experience in the comments below, or start a conversation by posting on your Activities page.