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Movement disorders specialists debate the usefulness of a new FDA-approved neuroimaging agent, 123I-ioflupane, that is intended to help differentiate parkinsonism from essential tremor.
DR. MARK STACY: “I think it is very useful in a patient with diagnostic uncertainty,” such as a patient with a mixed presentation not fully consistent with either parkinsonism or essential tremor… “I think it is also very useful for patients who have difficulty accepting the diagnosis of Parkinson disease,” for whom a scan provides objective evidence that the clinician's opinion may not.
The FDA has approved a new neuroimaging agent that offers nonspecialists the possibility of differentiating parkinsonism from essential tremor (ET). But many movement disorders experts believe it is almost certain to be overused and misinterpreted, driving up costs while offering little in the way of added benefit.
The agent, called 123I-ioflupane, approved in January under the trade name DaTscan (GE Healthcare), binds to dopamine transporters in the striatum, allowing them to be visualized by single photon emission computed tomography (SPECT), an imaging technology that is relatively inexpensive and widely available.
While new to the United States, DaTscan has been in use in Europe for over a decade, where it is approved for differentiating parkinsonism (from multiple causes) from ET, as well as distinguishing Lewy body dementia from dementia due to other causes. Estimates suggest that over 200,000 doses have been dispensed. The US approval does not include a dementia indication, and states that DaTscan “is an adjunct to other diagnostic evaluations.”
Mark Stacy, MD, professor of neurology and associate dean of clinical research at Duke University Medical Center in Durham, NC, has used DaTscan in his own practice, and has served as a consultant to the manufacturer during the approval process.
“I think it is very useful in a patient with diagnostic uncertainty,” such as a patient with a mixed presentation not fully consistent with either parkinsonism or essential tremor, Dr. Stacy said. “I think it is also very useful for patients who have difficulty accepting the diagnosis of Parkinson disease,” for whom a scan provides objective evidence that the clinician's opinion may not. “Clearly that's not one of the indications, but I think that's one way in which it will be used.” Is this a bad thing? “If it improves the confidence in diagnosis, I think it improves the confidence in care” that follow, Dr. Stacy said.
“Waiting will also tell you” what the correct diagnosis is, he said, but often patients don't want to wait. He likened it to a patient seen for a headache who insists on an MRI. “You'd allow that. When you get down to it, there is not a lot of difference” between that and a scan when parkinsonism is suspected. “I think neurologists are going to have to learn where this technique will be helpful to them.”
Joel Perlmutter, MD, is skeptical there is much use at all for the scan. Dr. Perlmutter, a neuroimaging expert who is head of the Movement Disorders Section and professor of neurology at Washington University School of Medicine in Saint Louis, MO, was invited by the FDA to give expert testimony to its advisory panel during the approval process.
His review of the literature stressed that neuroimaging cannot distinguish among the various parkinsonian conditions, whether Parkinson disease (PD), multiple system atrophy, progressive supranuclear palsy, or corticobasal degeneration. “All of them have the same appearance on the scan.”
While the scan can distinguish parkinsonism from essential tremor, “most of those cases aren't really major clinical questions for a person with movement disorders expertise,” he testified, although there are a few patients whose symptoms may be ambiguous, “and that is a reasonable conundrum.”
But while industry-funded studies tend to stress the ability of the scan to add to the clinical diagnosis at first presentation, “those not funded by companies have more measured interpretations.” In sum, he said, “the sensitivity and specificity are not good enough for altering clinical behavior.”
While a negative scan argues strongly against parkinsonism, Dr. Perlmutter said there was not enough evidence to rule it out completely. “That's risky,” he said. “Patients want to know, but this doesn't really tell them. If the doctor tells them 100 percent they don't have PD based on a negative scan, they don't understand the literature. My conclusion was, in no uncertain terms, the clinical utility was none.”
Discussions of cost effectiveness were ruled beyond the panel's purview, he said, despite the fact that the cost of a scan far exceeds that of a consultation and follow-up with a movement disorders expert. “I told the FDA panel, that even with essential tremor, it's cheaper to give people levodopa for six weeks, and do the follow-up exam to see if they respond, than to do a scan, which, if the scan is positive, will still leave you with the clinical question of whether it is levodopa responsive.” No pricing has been announced, but several estimates obtained by Neurology Today suggest the scan itself will likely cost between $1,000 and $2,000, not including follow-up.
The FDA decision “is disappointing as a direction for the field to be moving in,” said William Weiner, MD, professor of neurology at the University of Maryland Medical Center, director of the Maryland Parkinson's Disease and Movement Disorders Center, and a member of the editorial advisory board of Neurology Today. “Quite honestly, we expect medical students to be able differentiate between essential tremor and parkinsonism.” With its widespread use in Europe, Dr. Weiner asked, “has that improved their PD care over what we do in America? No. I don't think there is much value added.”
Kathleen Shannon, MD, associate professor of neurology at Rush University Medical Center in Chicago, concurred that “from the expert's standpoint, it's not going to offer a lot of utility. It's not a way to track progression, or decide on initial therapy, or decide how therapy should be changed.”
“When technology is widely adopted, you find a lot of inappropriate testing. I'm concerned that people will start ordering this test, and get a result that they are not really qualified to manage,” she said.
In very early PD, Dr. Weiner said, “there are real questions to discuss with the patient and family about whether they want to start medication or not,” based on the patient's symptoms. “I don't think that's what's going to happen” with the scan, he predicted. “There will be a huge marketing push by any company with a so-called neuroprotective drug. But there is currently no medication that alters the course of the disease. It's an unnecessarily expensive test that is going to lead to unnecessarily expensive treatments. At a time when our country is talking so much about what to do about medical costs, this does not add much value.”
Robin Elliott, executive director of the Parkinson's Disease Foundation, concurs that the best use of the scan should be a very limited one. “We feel deeply that people with PD need to go to very good doctors, someone who knows the disease forwards, backwards, and sideways. We've heard people say this would be wonderful for the general doctor out there who doesn't know PD that well. This is not a criticism of DaTscan, but it shouldn't be a distraction from getting the best medical care. A general practitioner plus DaTscan is not necessarily the best medical care.”
DR. JOEL PERLMUTTER: “Patients want to know, but this doesn't really tell them. If the doctor tells them 100 percent they don't have PD based on a negative scan, they don't understand the literature. My conclusion was, in no uncertain terms, the clinical utility was none.”
DR. KATHLEEN SHANNON: “When technology is widely adopted, you find a lot of inappropriate testing. I'm concerned that people will start ordering this test, and get a result that they are not really qualified to manage.”
Providing a European perspective, Niall Quinn, MD, emeritus professor of clinical neurology at University College London, estimated that at his center, at least 30 percent of referrals for scans are “inappropriate requests. So it is important to train people about when it is useful and when it isn't. I am glad it is available. It is helpful in tricky cases. But in most cases, if you are experienced, and you look very carefully at the patient and spend enough time on the history and examination, you don't need it.”Back to top