The path to a diagnosis of Parkinson’s can be a long and uncertain one. Some people have multiple chronic conditions, making it difficult for doctors to identify whether motor symptoms are caused by a disease or a medication.

Part of the criteria for a Parkinson’s diagnosis depends on how symptoms have progressed, when and in what order new symptoms appear, and whether any other condition could be causing them.

Parkinson’s is usually diagnosed by a neurologist. Receiving a diagnosis from an experienced specialist in movement disorders lowers the risk of misdiagnosis.

How Is Parkinson’s Diagnosed?

Parkinsonism is a syndrome, or collection of symptoms characterized by motor (movement) issues — bradykinesia (slowed movements), tremors, loss of balance, and stiffness. Parkinson’s disease (PD) is the most common type of parkinsonism, accounting for 80 percent of cases. Read more about types of parkinsonism.

Diagnosing parkinsonism is the first step. Parkinsonism is diagnosed when a person has bradykinesia and either rest tremor (tremors when the muscles are relaxed) or rigidity. From there, the neurologist decides whether Parkinson’s disease is the most likely cause of the Parkinsonism.

Here are some criteria that make a diagnosis of PD seem more likely:

• Dopaminergic drugs (drugs that influence dopamine levels), such as Levodopa/Carbidopa, significantly improve symptoms. Improvements increase with higher doses and decrease with lower doses.
• Levodopa/Carbidopa causes the side effect of dyskinesia — involuntary swaying, writhing, or head-bobbing movements.
• There is a loss of smell or evidence of certain cardiovascular problems.

Red flags that make PD seem less likely include:

• Motor symptoms are bilateral, appearing equally on both sides.
• Walking difficulties progress rapidly, and you need a wheelchair within five years.
• Motor symptoms do not progress over five years in people who are not medicated.
• Difficulty swallowing or speaking develops within five years.
• Certain respiratory (breathing) problems are present.
• Urinary problems develop within five years.

Criteria that exclude PD and tell the neurologist to look for other causes include:

• Use of medications (within the past year) known to cause motor symptoms
• Motor symptoms limited to the legs for more than three years
• High doses of Levodopa/Carbidopa do not help someone with moderate symptoms
• Normal images of the brain’s dopaminergic (dopamine-related) systems
• Certain eye movement problems
• Aphasia (loss of ability to speak or understand speech)
• Diagnosis with another condition that can cause motor symptoms

Based on all of the above criteria, the doctor will decide how probable a diagnosis of Parkinson’s disease is. Since several diagnostic criteria may involve waiting to see whether medications help and whether and how certain symptoms progress or appear, the precise diagnosis can take time to determine.

Tests and What They Show

Some tests can provide support for a diagnosis of Parkinson’s, while others are performed to 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. A clear picture may emerge from the medical history that will help a doctor assess risk factors that may strengthen the suspicion of Parkinson’s or rule out other conditions.

Neurological Exam

The doctor will ask questions to determine mental status, cognitive function, and mood. They will carefully examine your eyes and reflexes for signs of nerve damage. You will be asked to move your arms and legs in specific ways to test for weakness or lack of coordination. The doctor will test for loss of sensation by touching various parts of your body with a vibrating tuning fork, or sharp or dull items. The neurological exam provides an objective assessment of signs and symptoms that may suggest Parkinson’s or another condition.

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 Levodopa/Carbidopa 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.

DaTscan

A newer technology called DaTscan has been approved by the U.S. Food and Drug Administration (FDA) to help neurologists visualize dopamine-producing cells in the brain. DaTscan can help differentiate parkinsonism from essential tremor. DaTscan involves an intravenous injection of a radioactive chemical into the bloodstream. The head will then be imaged using a specialized camera. The chemical binds to dopaminergic cells. If the dopaminergic system appears normal in the scan, it is more likely that symptoms are caused by essential tremor. If the dopaminergic system appears abnormal, the doctor is more likely to consider a diagnosis of Parkinson’s. Side effects of the chemical used in DaTscan can include headache, vertigo, and a crawling sensation on the skin.

Imaging Scans

If a Parkinson’s diagnosis is in question, the 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

Between 10 percent and 15 percent of Parkinson’s cases are thought to be directly caused by a genetic defect inherited from parents. If your doctor suspects familial Parkinson’s, they may order a blood test to check for specific genetic markers. Blood samples can also be tested for evidence of cardiovascular problems that could be contributing to parkinsonism.

Ruling Out Other Conditions

The process of ruling out similar conditions is referred to as differential diagnosis. Parkinson’s has symptoms in common with Alzheimer’s disease, frontotemporal dementia, and Huntington disease. Parkinson’s symptoms can be caused by medications such as antipsychotics that may be taken for depression or schizophrenia. Parkinsonism can also be caused by another disease; this is known as secondary parkinsonism. Conditions that can cause secondary Parkinsonism include hydrocephalus (high pressure caused by fluid buildup in the brain), some types of brain tumors, Wilson’s disease, problems with the parathyroid gland, chronic liver failure, issues with the blood supply to the brain, and infections such as HIV, neurosyphilis, toxoplasmosis, and progressive multifocal leukoencephalopathy (PML).

Your doctor may be able to quickly rule many of these conditions based on your medical and family history or simple blood tests. Other disorders may require time and repeated tests before they can be confirmed or ruled out. The presence of other diseases in addition to Parkinson’s may complicate the differential diagnosis and eventually result in multiple diagnoses.

Condition Guide

• Parkinson’s Disease and Parkinsonism – An Overview
• Side Effects and Parkinson's
• Stages of Parkinson’s
• Symptoms of Parkinson’s
• Treatments for Parkinson’s and Parkinsonism
• Types of Parkinson’s
• What Causes Parkinson’s?