Parkinson’s diagnosis [Is a DAT scan/ F-DOPA PET scan needed?]

A DAT scan or F-DOPA PET scan can be used for Parkinson’s diagnosis.

But, Parkinson’s disease is primarily a clinical diagnosis.

In other words, an evaluation of symptoms & examination by a doctor experienced in Parkinson’s disease is usually sufficient for diagnosis and treatment.

Usually, your history a thorough examination is better than any testing for Parkinson’s disease.

Let us know these symptoms & signs, and understand when a DAT scan or F-DOPA PET scan is needed.

Symptoms of Parkinson’s disease

There are 4 main symptoms of Parkinson’s disease.

At least one of these symptoms is present, and slowness is almost always present.

  • Shaking = Tremor. This is the most easily recognized sign of Parkinson’s disease. Usually, the shaking only affects one hand or one leg in the early stages of the disease. The affected limb may shake both at rest, and while it is moving. Occasionally there might be shaking of the head.
    Shaking of hands is the most commonly recognized symptom of Parkinson’s disease.
  • Slowness = Bradykinesia. The patient’s movements become slow. Sometimes only the movements of a particular hand/leg become slow. But usually, there is some slowness of movement of the entire body. This is best noticed while walking. Relatives will often say “Well, she was one of the fastest walkers in the family. Now she walks slowly so that she gets left behind when we are walking in a group. After every 10 feet or so we have to wait so that she can catch up with us. Perhaps it’s old age…?”. This isn’t old age – It is frequently Parkinson’s disease and the good news is that it is curable.
    Walking slowly could be a symptom of Parkinson’s disease.
  • Stiffness = Rigidity. The patient’s body parts become stiff. This may be restricted to one hand so that, for the example, the patient has difficulty buttoning his shirt. A frequent complaint is that the patient is not able to reach the top of their head to comb or tie their hair. If a leg has become stiff, the patient may feel like he/she is dragging it while walking.
    Stiffness of the arms can make it difficult to comb hair, wear clothes or apply hair clips.
  • Imbalance The person feels unsteady while walking, or even standing. Falling is uncommon in the early stages but may become more frequent later.

 

Other symptoms useful for Parkinson’s diagnosis

Now, in addition to these three main symptoms, the patient may also have other features which support the diagnosis of Parkinson’s disease.

There are many problems with movement in Parkinson’s disease.
  • Postural instability: Many doctors/guidelines consider this to be a core symptom of Parkinson’s disease. The patient is unstable while walking. Falls are not common in the early stages of Parkinson’s disease. But the patient may appear wobbly while taking turns, or if given a slight nudge in a crowded place.
  • An expressionless face.
  • Bending forwards while walking.
  • Shuffling while walking.
  • Freezing or getting stuck while walking.
  • Decrease in dexterity, or fine motor skills such as drawing.
  • Problems with thinking or memory (Dementia).

Parkinson’s Misdiagnosis:

These features are usually enough to make a clinical diagnosis of Parkinson’s disease. However, before the diagnosis can be made, two important things need to be ruled out:

These problems look like Parkinson’s disease, so they are called Parkinson’s disease Mimics.

Parkinsons-Plus syndromes are diseases that appear to be just like Parkinson’s disease but are subtly different – e.g. in terms of eye movements, or early falls. These diseases have complicated names: Progressive Supranuclear Palsy (PSP), Multiple Systems Atrophy (MSA), Cortico-Basal Disease (CBD), etc…. These are further described here.

Certain medications can cause symptoms, just like Parkinson’s disease! This is an absolutely essential and often overlooked part of treating the patient. Some patients don’t require more medications, they require less!

Medications that can produce symptoms like Parkinson’s disease

Many medications used for psychiatric problems such as schizophreniaHaloperidol, Risperidal, Olanzapine, Aripiprzole, Trifluoperazine and many more. Clozapine and Quetiapine usually do not cause problems.
Some medications for mood and depressionFluphenazine, Tranycypormine, Lithium
Some anti-nausea medicationsMetoclopramide, Levosulpuride, High doses of domperidone about 30-40 mg/day, Flunarazine, rarely cinnarazine
Some heart and blood pressure medicationsAmiodarone, methly-dopa

Besides these two mimics, there are 30+ mimics which may be mistaken for Parkinson’s disease.

Additional testing for Parkinson’s

Many doctors I know make a confirmatory diagnosis of Parkinson’s disease at this stage. If there are no red-flags, then a single office visit is usually enough to confirm the diagnosis.

Some doctors, including myself, do request some simple investigations (see box below). These are done to rule out rare causes and Parkinson’s Mimics. Usually, these tests do not show an additional problem.

Optional tests to rule out rare causes
– MRI Brain – CBC, LFT, RFT – TSH, PTH, Ceruloplasmin – Blood smear for acanthocytes In my clinical practice, these investigations change management only in about 10% of cases.

DAT Scan & F-DOPA PET scan

Very rarely, the clinical diagnosis of a patient may be difficult. This can happen in two scenarios:

  • Very early Parkinson’s disease with very subtle symptoms.
  • When features of two different diseases are present – such as Parkinson’s disease and Essential tremor.
The diagnosis of Parkinson’s disease is usually very straightforward. Sometimes, it can be difficult.

In these cases, there are two options:

  • Treat with levodopa: if the patient responds he/she probably has Parkinson’s disease.
  • Do a DATscan or even better – a F-DOPA PET scan.

The DAT scan & the F-DOPA PET scans can measure Dopamine activity inside the brain. Unlike an MRI which can only look at the structure of the brain, these scans are actually able to look at Dopamine activity itself. The image below is of a DAT scan:

The F-DOPA PET scan is superior overall to the DAT scan. It has higher resolution and more accurately measures the Dopamine activity. It also faster (overall about 1.5 hours) than a DAT scan which takes about 5 hours to be completed.

f-DOPA-PET scan: Note the relatively decreased brightness in the FIRST image.

However, the F-DOPA PET scan is slightly more expensive and is not available in all cities. In cities where the F-DOPA PET scan is not available, a DAT scan is a reasonable alternative.

Read more:

  1. To know more about what to do before a FDOPA PET scan, click here: [Cedar’s Sinai patient guide]
  2. For more information about the DAT scan process, click here: [Cedar’s Sinai patient guide]

 

Is a DAT scan or F-DOPA PET scan always needed?

No! Not at all!

First, the diagnosis of Parkinson’s disease is obvious in most patients.

The proof of the pudding is in the eating. If you improve significantly with levodopa – you have parkinsonism.

If this improvement is consistent for many years – you probably have Parkinson’s disease.

The proof of the pudding is in the eating. If you respond well to levodopa, then you have Parkinsonism.

Second, while these scans are useful in differentiating some diseases like Essential tremor from Parkinson’s disease, they are not very useful in identifying mimics (e.g. the Parkinsons-plus syndromes).

Bottom line:

Your observation of your symptoms + your doctor’s clinical examination beats all testing for Parkinson’s disease! 

Doctor talking to patient about DBS for Parkinson's
Good communication = better diagnosis!

All of these, including the DAT scan & F-DOPA PET scan, are useful tools to facilitate testing for Parkinson’s disease.

Just like all tools in medicine, it is crucial to use them judiciously.

 


Caution:
This information is for educational purposes. It is not a substitute for professional medical diagnosis & treatment. Do not change your medications, supplements or other treatments without your doctor's permission.

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Dr. Siddharth Kharkar

Dr. Siddharth Kharkar is a board certified (American Board of Psychiatry & Neurology certified) Neurologist. He is a Epilepsy specialist & Parkinson's specialist in Mumbai, Maharashtra, India.

He has trained in the best institutions in India, US and UK including KEM hospital in Mumbai, Johns Hopkins University in Baltimore, University of California at San Francisco (UCSF), USA & Kings College in London.

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2 thoughts on “Parkinson’s diagnosis [Is a DAT scan/ F-DOPA PET scan needed?]”

  1. This was great info.
    I have essential tremor and have been on Quetiapine and Clozapine for the past decade for a presumed diagnosis of schiz-affective f25 however when removing antipsychotics from my regime it appears without a doubt I have PD.
    I also have Trigeminal neuralgia.

    I will see neurologist 17th march.
    Thank you for the info

    Please advise

    Reply
    • I am happy it was helpful. There is certainly a group of people who have features of both ET and PD. . I think a careful examination by a neurologist and if needed an F-DOPA/TRODAT scan should give you some clarification.

      Reply

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