What is Parkinson Disease?

As with any other medical condition the diagnostic process begins with the history and physical examination. Parkinson disease is really considered a clinical diagnosis and this means that it is diagnosed based on characteristic findings on the clinical examination. These are described above in the section on the motor symptoms of Parkinson disease. A tremor associated with slowness of movement, rigidity of the arms and a stooped posture of the body whilst walking are all commonly found on the clinical examination of  a patient with Parkinson disease. Postural instability and falls tend to occur later in the course of the illness. The symptoms tend to begin on one side. The range of symptoms may be mild to severe. Another means of establishing the diagnosis is assessing the response to dopamine treatment. The dopamine treatment (described below) essentially tops up the dopamine levels in the brain thereby treating the movement issues in Parkinson disease. It is considered supportive of the diagnosis when there is a good response to this medication. It should be noted however that of all the symptoms of Parkinson disease it is the tremor that may be the least responsive. So in looking for a response to treatment in support of a diagnosis of Parkinson disease it is really the slowness of movement, slowness of walking and rigidity of the arms that should improve.

The purpose of the history and physical examination is also to identify other potential causes for the symptoms. For example, there are a few unusual conditions that may seem like Parkinson disease but are caused by something else. These conditions will be described below. Your neurologist will be able to distinguish between these and decide which is most likely.

Some blood tests may be done also. There is no single blood test that can diagnose Parkinson disease; however, your neurologist may wish for you to have blood tests to rule out other conditions. For example, there is a condition called Wilson’s disease which is a disorder of copper metabolism. It has some clinical features that may be similar to Parkinson disease. A simple blood test will help decide if this is the underlying diagnosis.

Other investigations that may be carried out include brain scans. An MRI of the brain should be normal in Parkinson disease. Therefore, it is not done to make the diagnosis but rather to rule out other possible diagnoses. So if your neurologist thinks that you have Parkinson disease based on the history and clinical examination you will not need to have an MRI scan. The scan that is specific to Parkinson disease is called a DAT scan. Essentially this evaluates the dopamine producing areas of the brain and helps decide if the dopamine production is sufficient. The DAT scan can help decide if your symptoms are in fact due to Parkinson disease. It cannot, however, tell if your symptoms are due to a different form of “Parkinsonism” that are the other conditions that may look like Parkinson disease but are actually caused by a distinct condition. (described below). In order to do that an even more specialised scan is warranted. This is called a PET (Positron Emission Tomography) scan and it can look at glucose metabolism in the brain. It can tell if there are areas that are not metabolising glucose as they should be and the pattern of this abnormality can help make the diagnosis- it should be noted however that this is a very specialised scan, it is not widely available and will be requested only by a neurologist.