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Currently, there are no blood tests or imaging scans to accurately diagnose Parkinson's disease. The clinical diagnosis of Parkinson's disease is determined by the evaluation of the patient's symptoms. It is very important that the physician examining the patient (usually a neurologist) have the skill and experience needed for diagnosing movement disorders since Parkinson's disease is misdiagnosed in 25-35% of cases. The incidence of misdiagnosis declines sharply when the patient is evaluated by a doctor who specializes in Parkinson's disease and other movement disorders.

The diagnosis of Parkinson's disease is established on the basis of the following evaluations and studies:

• Neurological evaluation
• Laboratory evaluation
• Imaging Studies

Neurological Evaluation of Parkinson's Disease

The physician performs a neurological evaluation to determine which symptoms of the four TRAP symptoms are present (i.e., tremor at rest, rigidity, akinesia, or postural instability) and their severity. However, these symptoms do not always present themselves in a way that clearly points to Parkinson's disease.

Many physicians use a test called the Unified Parkinson's Disease Rating Scale (UPDRS), which is a very sensitive indicator of signs of early Parkinson's disease in particular and of the presence Parkinson's disease symptoms in general. The test consists of three parts:

• The first part consists of information collected from the patient and family members regarding the difficulty of performing routine activities of daily living at home, (e.g., dressing, bathing, showering, eating, walking).
• The last two parts of the test involve an intensive physical examination and neurological evaluation by the physician in which he/she will focus on presence and severity of TRAP symptoms (e.g., getting out of a chair, walking with a normal stride, swinging the arms symmetrically).

Sometimes, to confirm a diagnosis of Parkinson's disease, the physician may prescribe antiparkinson medication to see if the patient responds (i.e., shows improvement in walking, movements, or tremors). This information is then used to either rule-out or establish the diagnosis of Parkinson's disease.

Laboratory Evaluation of Parkinson's Disease

Although there are no laboratory tests to establish the diagnosis of Parkinson's disease, many physicians order some of the following tests in order to rule-out other underlying conditions:

• Complete blood count (CBC)
• Liver function test
• Thyroid function test
• Drug/Toxicology screen (if appropriate)
• Serum ceruloplasmin (a copper-carrying protein) and 24-hour urine copper excretion
• Liver biopsy

Imaging Studies for Parkinson's Disease

If the diagnosis is still not clear after physical and neurological evaluation, the physician may order neuroimaging tests, including:

• Positron Emission Tomography (PET) in which a radioactive tracer called 18-fluorodopa is injected intravenously while a scanner measures the uptake of the tracer in the substantia nigra portion of the midbrain and thus determines number of dopamine cells present.

• Single Photon Emission Computed Tomography (SPECT) which is similar to a PET scan but uses a different radioactive tracer and measures the uptake of the material in the brain differently.

Neither of these neuroimaging tests is ordered often since they are very expensive and not always covered by insurance.