ARTICLE IN BRIEF
In a pooled analysis of data, DaTscan imaging — which involves the injection of a radioactive agent that binds to dopamine transporters (DaT) in the brain — yielded a 91-percent sensitivity rate and a 92-percent specificity rate in diagnosing parkinsonian syndrome; and a 78-percent sensitivity and 90-percent specificity for differentiating dementia with Lewy bodies from Alzheimer's disease.
PHILADELPHIA—A pooled analysis of data from multiple trials suggests that DaTscan imaging — a neuroimaging technique that uses a radioactive agent that binds to dopamine transporters (DaT) in the brain — was useful in differentiating parkinsonian syndrome (PS) from other movement disorders, as well as dementia with Lewy bodies (DLB) from Alzheimer's disease.
In 400 patients, the data showed that DaTscan had a 91-percent sensitivity rate and a 92-percent specificity rate in diagnosing PS. In more than 326 cases, DaTscan was found to have a 78-percent sensitivity and 90-percent specificity for differentiating DLB from Alzheimer's disease, a researcher from Scotland reported here at the AAN Annual Meeting.
Donald Grosset, MD, a consultant neurologist at the Institute of Neurological Sciences and honorary professor at the University of Glasgow, said the compilation of data from the 726 intent-to-treat cases confirms that the technology should be considered for use in cases of uncertain diagnosis of Parkinson's disease and dementia. He made his remarks on behalf of centers in five countries that participated in the trials, as well as GE Healthcare, the sponsor of the trial and the developer of the technology.
DaTscan involves the injection of ioflupane I 123 FP CIT, a radioactive agent used with single photon emission computed tomography. The agent helps image-readers assess the “inverted comma” pattern of the dopamine transporters in the caudate-putamen area of the brain — any erosion of that symmetrical, double-crescent pattern is seen as abnormal.
Differentiating the presynaptic dopaminergic deficit of parkinsonian syndrome from those without this deficit can be difficult, Dr. Grosset noted. Normal dopaminergic imaging has been found in as many as 4- to 14-percent of cases that were diagnosed as early Parkinson's disease, several earlier studies have shown.
THE STUDY METHODOLOGY
In this analysis, data were combined from the four trials used to support the approval of DaTscan in the United States for the diagnosis of Parkinson's disease. The technology is already approved in Europe for diagnosis in cases of suspected DLB, but that use is not approved in the US.
The researchers were trying to use the imaging to differentiate either established PS, uncertain PS, or early PS from essential tremor. In each of the trials, the patients had been clinically diagnosed — for 102 of the patients, a panel of physicians made the diagnosis. The researchers compared the clinical diagnosis with the findings from the DaTscan images that were reviewed by a panel of three to five blinded experts, by on-site nuclear medicine physicians, or both.
“A simple visual assessment of the FP CIT DaTscan gives a high level of sensitivity and specificity,” Dr. Grosset said. “This sort of test is helpful as a diagnostic adjunct in uncertain cases.”
There are a number of reasons why it is difficult to diagnosis PS, Dr. Grosset explained. There may be incomplete clinical features in some patients; adult-onset dystonic tremor may mimic the tremor of Parkinson's; and sometimes, drug-induced parkinsonism can't be identified because withdrawal from the drug might not be feasible.
Using the technology can help avoid incorrect diagnoses — false positives are especially problematic, Dr. Grosset said. “It's clinically more relevant because a false positive diagnosis of Parkinson's disease will take the patient potentially down the wrong treatment avenue,” he said.
Anthony Lang, MD, the Lily Safra chair in movement disorders at the University of Toronto, said the findings from the meeting summarize what's been previously reported, bringing together a larger number of cases.
“This is a useful tool for differentiating patients with PD and other causes of nigral dopaminergic degeneration — multiple system atrophy, and progressive supranuclear palsy — from patients who lack this feature — [such as those who have] early tremor, a small proportion of which might be confused with PD especially when they have rest tremor, and patients who might have some parkinsonian features not due to PD, such as vascular parkinsonism, depression with arthritis, psychogenic parkinsonism,” Dr. Lang said.
“The main criticism in these cases is that most of the time a careful exam, with appropriate follow-up and further assessments, will obviate the need for DaT scanning,” he said. He generally agrees with this view.
But, he added, “I do believe that, when used judiciously, it can provide useful information that can influence patient care as has been shown.”
He noted that it might, for example, encourage greater use of a cholinesterase inhibitor for cases involving DLB. Another benefit of using DaTscan to identify Parkinson's, he added, is that it may rule out using certain therapies, such as certain neuroleptics, apart from quetiapine and clozapine.
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