Diagnosis

• There are no set tests to confirm Parkinson’s disease in an individual. Many neurological examinations and diagnostic tests are carried out before diagnosis of a patient. One of the most accurate methods to diagnose a patient is by the use of a specialised PET scanner and even these results can sometimes prove inconclusive.The clinical features of the patient must be fully assessed and history of early symptoms analysed.

Neurologic examination

• Involves the evaluation of the symptoms and particular movement disorder that the individual may be experiencing. The procedure involves the analysis of the individuals’ medical history along with a physical evaluation. The doctor will typically observe the patient carrying out simple everyday activities in order to detect any dyskinesias or mobility problems which could be associated with the disease. Coordination and a balance will also be observed. The main aim in this investigation is to gain a thorough evaluation of the nervous system.

A positive glabellar tap sign

• A typical physical test whereby the patient has a sustained blink response to tapping between the eyes can be used in recognition of Parkinson's disease. In those individuals not suffering from Parkinson's disease the blink response is diminished on repetitive tapping where a Parkinsonian patient cannot usually supress the reflex but again this test stands for limited diagnostic value.

Clinical Tests

Brain imaging: 

• These are thought to be useful in excluding other causes of the Parkinsonian symptoms being experienced. There are two main types of scan initially used in the diagnosis of Parkinson’s disease. The computerised tomography scan (CT) and the magnetic resonance imaging scan (MRI). Both of these scans appear normal in Parkonsonian patients due to the neuronal defect being too small to detect via these imaging methods. When abnormal scan results are seen it is thought to be due to secondary parkinsonism and not the idiopathic form of Parkinson’s disease, whereby a structural lesion has been experienced perhaps relating to, for example, strokes.

• Due to these reasons it is often thought not to be useful, by most specialists, to carry out such imaging procedures as the majority of the scams appear normal upon development. In short, these scans are used when there is thought to be possibility of an alternative cause of Parkinsonian symptoms.

Positron-emission tomography (PET scanning):

• This type of scanning allows the detection of various chemicals of the brain. The procedure carried out begins with the intravenous injection of a radioactive compound (in small concentration). This compound is taken up by the appropriate areas of the brain appropriate. For example, in PET scanning for Parkinson’s, the compound usually used is fluoro-dopa, due to it being taken up by the unharmed dopaminergic neurons of the brain. The dark patches on such a scan therefore refer to the lack of dopaminergic cells in the brain due to the Parkinsonian effect, therefore resulting in no uptake of the radioactive chemical in these regions.

• There are low levels of fluoro-dopa fluorescence seen in the striatum on scans of patients with Parkinson’s disease. 

  

  The observation of the pattern of loss of dopaminergic cells in this way can be useful in distinguishing between Parkinson's disease and syndromes which may have similar symptoms such as Parkinson-plus syndromes, for example there appears to be a concentration of involvement of fluoro-dopa in Parkinson's disease.

• The problem experienced with this form of scanning is that there are few centres in the UK which have the equipment needed to carry out this scan due to the need to have on-hand radioactive substances to carry out the procedure which decay rapidly, therefore limiting their transport. It is for this reason that this method is reserved purely for in research into such disorders and not used as a means to diagnose Parkinson's disease.

 Image Courtesy of user chris 73 of wikimedia commons

DatSCAN:

The DaTSCAN is a means of detecting the levels of dopamine activity in the brain which is similar to the PET scan but the scan is less sensitive therefore producing lower resolution images. The equipment needed for this method is much more widely available and therefore can be used for patient diagnostic purposes. The scan allows us to distinguish between Parkinsonian patients and those who may be experiencing essential tremor, a symptom also seen in Parkinson's. The process is helpful particularly in those where their clinical diagnosis is uncertain, but the accuracy of the diagnostic ability of such a method questionable.

L-Dopa challenge:

This procedure involves the assessment of reaction to Levodopa treatment by the administration of a single dose of the drug orally. It is assumed that if the drug appears to alleviate the symptoms of the patient in any way then it is a good indication of Parkinson's disease. However, many Parkinsonian patients who are experiencing milder symptoms of the disease are unable to show a marked improvement in symptoms, therefore making the response to such a test difficult to interpret.

It has also been suggested that administration of a single dose of levodopa can lead to increased susceptibility to diskinesias which are seen in treatment of the disease using this drug. This test therefore proves to have varying significance of results as regards the diagnosis of Parkinson's disease.

Apomorphine Test:

A test which provides an alternative way to assess dopaminergic responsiveness in diagnosis of the disease. The test follows the same principal as the L-Dopa challenge but the drug used here is apomorphine, a dopaminergic agonist used to treat Parkinson's disease.This test must also be carried out with the administration of the antiemetic domperidone due to the nausea and vomiting-inducing capabilites of the drug.This test is seen to be of less harm to the patient as it does not appear to result in increased risk of dyskinesias but again the sensitivity in relation to diagnosis is not known.

This animation is courtesy of user C6541 of Wikimedia Commons.

Many other tests should be performed in the attempt to diagnose Parkinson's disease in order to rule out possibilities of other disorders which may have similar symptoms. For example, simple blood tests should be undertaken to rule out possibility of anaemia which may cause a patient to feel dizzy and weak. Thyroid function should be tested due to hyperthyroidism causing tremor and hypothyroidism contributing to lethargy. Finally urine copper levels should be assessed to rule out Wilson's disease which is known to cause young onset Parkinsonism and therefore may mimic symptoms of ideopathic Parkinson's disease.