Detecting Dopamine Loss for Parkinson’s Diagnosis and Monitoring

Although there is no specific test for Parkinson’s disease, recent advances in a diagnostic imaging technique may help doctors identify high risk patients even before the symptoms of Parkinson’s disease appear. It may also serve as a tool to monitor disease progression. Parkinson’s disease is a neurodegenerative disease where there is a gradual progressive loss of dopamine nerve cells (dopaminergic neurons) in the brain. Currently Parkinson’s disease is identified by a clinical diagnosis where the medical history and clinical presentation allows a doctor to reach the diagnosis. However, the new diagnostic technique may allow for conclusive diagnosis and even help prevent misdiagnosis of the disease.

Low Dopamine Levels in Parkinson’s Disease

As explained under Parkinson’s disease brain chemistry,  dopamine is a brain hormone (neurotransmitter) that is deficient in PD patients. This is accompanied by a loss of dopaminergic neurons. When more than 60% of these neurons in the substantia nigra and corpus striatum of the brain are lost then the motor signs of Parkinson’s disease becomes evident. L-dopa may therefore help to counteract these symptoms by restoring dopamine levels. When dopaminergic neurons are stimulated, it is released at the nerve terminal into the gap junction known as the synapse. This dopamine is recycled by dopamine transporters (DaT) which pumps it back into the nerve cells and stored for use at a later stage.

Detection of DaT Activity

A substance developed by GE Healthcare known as DaTscan can help to detect these dopamine transporters. If the transporters are working then it indicates the presence of healthy dopaminergic neurons. Until now there was no significant structural change in the brain that were detectable by conventional imaging techniques. Therefore the loss of these dopaminergic neurons could not be isolated in the living patient although microscopic evaluation of brain tissue post mortem noted pallor of the substantia nigra and the loss of these neurons. With the use of DaTscan, dopaminergic neurons are highlight on a SPECT scan. This is type of nuclear imaging study that stands for single-photon emission computerized tomography (abbreviation~ SPECT). DaTscan is a contrast agent that is visible on a SPECT scan.

DaTscan Results

With DaTscan, the brain function can be evaluated rather than just the structural changes associated with Parkinson’s disease.  Healthy dopaminergic neurons are illuminated on a SPECT scan with the use of the DaTscan contrast agent. Therefore the more illuminated areas, the greater the number of healthy neurons. Conversely, dark areas indicate low dopamine activity.

This test holds much promise for accurately identifying patients with Parkinson’s disease or other parkinsonism syndromes. It removes uncertainty associated with undiagnosed or even misdiagnosed cases. While it may not be necessary for every PD patient to confirm the diagnosis, it is hoped that this scan will be a reliable technique to monitor progression of the disease and therefore any treatment that can slow its progression. Currently (August 2011) clinical trials are underway by some 14 medical centers in the United States to evaluate DaTscan as a means of monitory disease progression. This is part of the biomarkers study by the Michael J. Fox Foundation known as the Parkinson’s Progression Markers Initiative.

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