TUESDAY, Dec. 3, 2002 (HealthDayNews) -- U.S. physicians will have to continue to rely on their physical assessment skills to make a diagnosis of Parkinson's disease.
In Europe, a new test is making the diagnosis more definitive in at least 80 percent of cases, advocates say, but the DaTSCAN is unlikely to reach this side of the Atlantic anytime soon.
The United States lacks a manufacturer of the radioactive isotope needed, and the isotope must be used within 13 hours of being processed, making importing it impossible, says Dr. David Tuite, a radiology resident at Adelaide and Meath Hospital in Dublin, Ireland.
"As they have no manufacturing facility in North America, this prohibits its use in the U.S.A.," Tuite says.
Tuite presented the findings of an ongoing study of the DaTSCAN today at the Radiological Society of North America's annual meeting in Chicago.
"We're the first to use it in our country," Tuite says. "I imagine in time it will become the standard."
The DaTSCAN is "a radio pharmaceutical which labels dopamine in the brain," Tuite says. Patients with Parkinson's begin to have symptoms of the disease after losing 80 percent of the dopamine in their basal ganglia, a brain region involved in motor control and movement, he explains.
"The technique requires nuclear medicine facilities" and can be used to differentiate Parkinson's disease from essential tremors, another disorder that resembles the tremors of Parkinson's but whose cause is unknown.
Many people with essential tremors are placed on medication that doesn't help them and don't receive the medication they should when they are mistakenly thought to have Parkinson's, Tuite says.
About 1 million to 1.5 million Americans are diagnosed as having Parkinson's. But in post-mortems -- the only definitive way to diagnose the disease in the United States -- only 75 percent of them are found to have it, Tuite says.
"One-quarter have been misdiagnosed" and actually have essential tremors, Alzheimer's disease or something else, he says.
For his study, Tuite and his fellow researchers used DaTSCAN on 50 patients thought to have Parkinson's, but whose physicians weren't sure this was the correct diagnosis. The test proved valuable in confirming that many patients had the disease and some did not, based on dopamine levels that were detected. The test was 80 percent accurate at identifying Parkinson's when a person had it. And it was 30 percent accurate at giving a negative result if a person did not have Parkinson's, Tuite says.
The test was most useful in distinguishing whether patients with tremors had Parkinson's or essential tremors.
Tuite says he has received many requests from patients for the test.
Dr. Abraham Lieberman, medical director of the National Parkinson Foundation, says that while the DaTSCAN test may prove valuable, he doesn't consider it "earth-shattering."
It's not entirely conclusive, he says, although it can be used to verify a diagnosis of Parkinson's in people who have tremors. As Lieberman notes, this leaves out many people with Parkinson's because "about 30 percent of those with Parkinson's don't have tremors."
Dr. Kenneth Marek is president of the Institute for Neurodegenerative Disorders. He says the DaTSCAN test is "part of a larger approach to improving diagnosis" of Parkinson's disease and potentially halting its progression.
Marek says the production of high-grade iodine for radioactive isotopes is limited in North America. Although he uses it for research, he gets his limited supply from Vancouver, Canada. "This isn't a readily available source of radioactive iodine."
He says he's heard that companies that manufacture the isotope in Europe aren't anxious to open a plant in North America due to a lack of financial incentives. If the isotope and DaTSCAN were available in the United States, Marek believes it would be a valuable tool "to settle the diagnostic question."
What To Do
To learn more about Parkinson's disease, visit the
Parkinson's Disease Foundation Inc. or the
National Parkinson Foundation.
