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How is Parkinson's disease diagnosed?

Dr. Nader Pouratian, MD
Neurosurgeon

Parkinson’s disease is diagnosed based on clinical examination. There are no blood tests or brain scans that can definitively diagnose this disease. The diagnosis of Parkinson’s disease requires that a patient meet at least three of the following four criteria: slowness of movement (bradykinesia), stiffness (rigidity), rest tremor and assymetric onset (i.e., affects one arm or leg more than the other). In addition, patients must be able to show that their symptoms improve with levodopa (i.e., Sinemet) or a dopamine agonist (e.g., ropinirole). Finally, there must be no evidence of atypical parkinsonism such as abnormal eye movements or early signs of walking problems, loss of bladder or bowel function or dementia. While brain scans cannot be used alone for diagnosis, PET scans and DaTscan can be used to distinguish patients with parkinsonism from other patients, such as those with essential tremor.

There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic Parkinson's disease. Therefore, the diagnosis is based on the medical history and a neurological examination of the patient. The disease can be difficult to diagnose accurately. Early signs and symptoms of the disease may sometimes be dismissed as the effects of normal aging. A physician may need to observe the person for some time until it is apparent that symptoms are consistently present. Doctors may sometimes request brain scans or laboratory tests to rule out other diseases. However, computed tomography (CT) and magnetic resonance imaging (MRI) brain scans of people with Parkinson's disease usually appear normal. Since many other diseases have similar features but require different treatments, making a precise diagnosis as soon as possible is essential so that patients can receive the proper treatment.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

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Parkinson's can be difficult to diagnose because there is no test to provide a clear answer. Often doctors base diagnosis off a neurological exam and your family and medical history. Going over your history can help rule out other reasons you may be experiencing Parkinson's-like symptoms. Other disorders, medication, toxins, head traumas, or strokes could produce similar symptoms, so ruling those out is important. Then a doctor will likely ask you to walk around so they can examine your coordination.

Beyond that, diagnosis is dependent on your symptoms. A doctor will look for at least two of the common symptoms. Those symptoms should occur either only on one side of your body, or more pronounced on one side. Tremors should worsen when the body is rest. Finally, you may be placed on a medication (levodopa) to see how your body reacts. If you see dramatic results, Parkinson's is likely the cause.

Doctors can usually diagnose Parkinson's disease by talking to the person about his or her symptoms and seeing the problems he or she has. There’s no test that tells for sure it’s Parkinson’s disease. Sometimes the doctors do a scan that looks inside the brain to see if there’s enough dopamine.

There is no single test to diagnose Parkinson's disease. The condition is generally diagnosed by ruling out diseases with the same symptoms. MRI scans and blood tests can rule out other diseases. People who exhibit at least two of the four hallmark symptoms and who response to the drug levodopa are said to have Parkinson's.

Parkinson’s disease is a clinical diagnosis, which means it is diagnosed based on the way people describe their symptoms and the results of their physical exam. It cannot be diagnosed with a lab test or imaging test alone, although doctors sometimes will order tests such as an MRI to rule out other conditions.

Some newer types of tests called functional imaging tests can help support a diagnosis of Parkinson's disease. They include a type of medical imaging test called FDOPA-PET, blood tests and spinal fluid tests.

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