VANCOUVER, British Columbia — When the contrast agent ioflupane with iodine-123 (DaTscan, GE Healthcare) is used with single-photon emission computed tomography(SPECT) to diagnose early-stage Parkinson's disease, it performs as well as clinical assessment at 1-year follow-up, according to a new study.
The method could improve the diagnosis of early-stage disease and help ensure that patients get put on the right therapeutic regimen from the outset.
"We found that getting early imaging did change the management of patients, particularly for those patients who had positive scans," lead investigator John Seibyl, MD, chief executive officer, cofounder, and senior scientist at the Institute for Neurodegenerative Disorders, in New Haven, Connecticut, told Medscape Medical News.
"The physician was more certain that there was a diagnosis of a Parkinson's and was more likely to treat that patient with medication," he explained.
Dr. Seibyl presented the results here at the Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2013 Annual Meeting.
The researchers analyzed data from 2 clinical trials — PDT304 and PDT409.
In the PDT304 study, images from 179 people presenting with early characteristics of Parkinson's syndrome were assessed independently by 3 nuclear physicians. Three years after imaging, investigators compared the results with consensus clinical diagnoses made using video assessment.
Specificity was better for baseline imaging diagnosis than for baseline clinical diagnosis (95.4% vs 52.4%; P = .0005), as was positive predictive value (95.8% vs 69.7%; P < .0001).
Specificity was better for 4-week clinical diagnosis (after imaging results became available) than baseline clinical diagnosis (92% vs 48%; P < .0001), as were positive predictive value (93% vs 65%; P < .0001) and negative predictive value (98% vs 72%; P = .009). They remained better for 12-week and 1-year clinical diagnoses.
Table. Changes in Diagnosis and Clinical Management in Patients in the PDT409 Study
| Basis of Diagnosis | Change in Diagnosis, % | Change in Management, % |
| Clinical information | 9–23 | 22–31 |
| Ioflupane with iodine-123 imaging | 45–54 | 41–50 |
"If someone walks in the door of a movement-disorder or neurology clinic, what is the likelihood that you are going to get an accurate diagnosis?" Dr. Seibyl asked. "These data suggest that the scan performs just as well at that first visit as waiting a year to make a clinical diagnosis using all available clinical tools."
For patients with positive DaTscan images, the team found that treating physicians felt more confident about the diagnosis of Parkinson's, and were more likely to prescribe medication and increase the medication dose.
Dr. Seibyl attributed this difference to greater physician certainty that the patient had a disorder that would respond to dopamine replacement therapy.
Not only can an earlier diagnosis get patients on the correct medication, it can also help eliminate the use of unnecessary medications, with their accompanying adverse effects, Dr. Seibyl noted.
This work will play a critical role if disease-modifying agents are eventually developed for Parkinson's. "The goal is getting the tools in place so that we can make early and accurate diagnoses when such therapies become available," he explained.
The results are encouraging, but the next step is to determine whether the changes in management ultimately benefit patients, said Dan Silverman, MD, from the University of California at Los Angeles, who was not involved with the study.
"Unfortunately, so much of the work in radiology and medicine never gets beyond that step to test whether those changes benefit or even harm patients," Dr. Silverman told Medscape Medical News.
Still, he said he agrees that the study provides strong evidence of the diagnostic utility of the contrast agent. "I think anybody who has been following this research would be pretty convinced that when you have discordance between what you think clinically in the beginning and what you think based on a DaTscan, you're a lot better off with the DaTscan."
This study was funded by GE Healthcare, the manufacturer of DaTscan. Dr. Seibyl consults with Navidea Biopharmaceuticals, GE Healthcare, and Piramal imaging. Dr. Silverman has disclosed no relevant financial relationships.
Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2013 Annual Meeting: Abstract 191. Presented June 10, 2013.
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Cite this: New Contrast Agent Enables Earlier Diagnosis in Parkinson's - Medscape - Jun 18, 2013.
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