Diagnosis - Types of Imaging Used
Imaging tests use medical equipment to takes pictures of the body, showing what is occurring on the inside. There are several different imaging tests that may be used to assist doctors in making a diagnosis of Parkinson’s disease (PD), as well as ruling out other conditions. However, many of these tests are expensive, not covered by insurance, and do not necessarily help with the diagnosis. More advanced imaging techniques that can diagnosis the disease, such as imaging the presence of aggregates of the protein synuclein, are actively being researched.
Magnetic resonance imaging (MRI) is a test that uses powerful magnets and radio waves to generate pictures of the internal structures of the body. MRI is often used to view the brain and surrounding nerve tissues. MRI is useful to exclude strokes, tumors, hydrocephalus, multiple system atrophy, progressive supranuclear palsy, or Wilson disease. MRI is recommended in those patients whose symptoms do not provide a high degree of certainty, including those who lack a tremor or who are younger than 55 years of age. MRI can potentially be used to measure structural changes to the substantia nigra, an area of the brain that is affected by the disease processes of PD.1-3
PD is at least partially caused by loss of dopamine neurons. DaTscan is a special technique that provides detailed images of the dopamine neurons (nerve cells) in the brain. The Food and Drug Administration (FDA) approved the use of DaTscan for differentiating PD from other conditions in 2011. The patient is given a radioactive agent into a vein. This radioactive agent is absorbed by the brain’s dopamine cells, which can then be seen on SPECT (single photon emission computed tomography) scanning. PD causes a reduction in dopamine neurons. While a DaTscan cannot diagnose PD, it can be used to help confirm a diagnosis. However, it cannot distinguish between PD and diseases like multiple system atrophy or progressive supranuclear palsy, which also reduce the amount of dopamine in the brain. The DaTscan does not currently provide results that are more reliable than a neurological exam by a movement disorder specialist and as such, it is not routinely used.4,5
Positron emission tomography (PET) scans may be used in diagnosing PD, although they are not routinely used. Prior to a PET scan, the patient is given an intravenous (IV) injection of a radioactive substance called a tracer. The tracer is absorbed into the body, providing imaging of different components or abnormalities within the brain. During the scan, the patient lies flat on a table, which slides into a large tunnel-shaped scanner. The computer creates 3-D images on the monitor. PET scans can be used to see the activity of the neurotransmitter dopamine, which is affected by PD, or the levels of glucose, which may be a potential marker for disease progression.1-3
Computed tomography (CT) scans use special x-ray equipment to make cross-sectional views of the inside of the body. The patient lies flat on a table while the CT scanner rotates around the body, taking pictures at different angles or in a spiral pattern. Modern CT scans create three-dimensional (3-D) pictures of the inside of the body, enabling doctors to view small abnormalities. Usually, CT scans are used to rule out other conditions, rather than to definitively diagnose PD.1,2
Other tests used to diagnose Parkinson’s disease
Diagnosis of PD is generally made using a medical history and a physical exam. In addition to these tests, the patient presenting with Parkinsonian symptoms is usually given treatment with the medication levodopa. The relief of symptoms with levodopa is a sign that symptoms are caused by PD.6
An active area of research is discovering “biomarkers”, which are molecules in the blood, urine, or cerebrospinal fluid that can reliably diagnose Parkinson’s disease.