There is no single test to diagnose Parkinson’s disease. Health care providers use a combination of symptoms, physical examination, response to medication and, less often, imaging studies to determine if a person has Parkinson’s disease or another related disorder.
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When Parkinson’s disease is early or mild it can be difficult to diagnose because not all symptoms may be present. According to the April 2006 Neurology, 5 to 10 percent of people with Parkinson’s disease are initially misdiagnosed with another condition. To make the diagnosis, providers use a set of criteria. A major one is the presence of slowed movement, or bradykinesia. This can cause decreased facial expression, fewer spontaneous movements and a slow, shuffling walk. Another is tremor, or shaking, of the hand, foot or face. This may initially involve just one finger, and it happens when the involved body part is at rest. Rigidity, or muscle stiffness, may also be present. It can make a person swing the arms less than normal when they walk. These symptoms are generally worse on one side of the body. A fourth major sign of Parkinson’s disease — postural instability, or poor balance — tends to occur later than the other symptoms.
Response to Levodopa Medication
The movement symptoms of Parkinson’s disease result from loss of brain cells that make the vital chemical messenger dopamine. When a person with Parkinson’s disease is treated with levodopa, also known as L-dopa, some of the missing dopamine is temporarily replaced and their symptoms improve. This “levodopa challenge test” can be helpful in making the diagnosis, but some people with very mild or early Parkinson’s disease will not improve with the medication. When used alone, levodopa can have side effects of nausea, vomiting and low blood pressure. To prevent these, people are either pre-treated with the medication domperidone or given the combination drug carbidopa-levodopa.
Currently there is no imaging study that can definitively diagnose Parkinson’s disease. However, certain types of imaging may be useful to distinguish between Parkinson’s disease and similar disorders. For example, a person with only a tremor could have Parkinson’s disease or a different condition called essential tremor. A type of brain scan called single-photon emission computed tomography, or SPECT, might help to determine which type of tremor the person has. Alternately, another type of picture of the brain called an MRI scan could be helpful in distinguishing Parkinson’s disease from certain other disorders with similar symptoms.
Distinguishing Parkinson’s Disease From Similar Disorders
A number of other disorders exist that share some features with Parkinson’s disease. Among these are vascular parkinsonism (due to blood vessel problems in the brain), multiple system atrophy and progressive supranuclear palsy. In order to distinguish between these disorders and Parkinson’s disease, health care providers consider several factors. For example, if a person has balance problems with falls as one of their first symptoms, they are less likely to have Parkinson’s disease. Parkinson’s disease is also less likely if the movement symptoms are equally bad on both sides, if they progress rapidly and if there is no tremor. Early appearances of “autonomic symptoms” — problems with urinary or bowel accidents, erectile dysfunction or low blood pressure upon standing — also points away from Parkinson’s disease. Finally, lack of response to levodopa medication could suggest one of these other disorders.