SPECT shows promise in diagnosing Parkinson's

Clinical evaluation is the standard by which Parkinson's disease (PD) and parkinsonian syndrome (PS) are currently diagnosed. But a new study suggests that functional SPECT neuroimaging with the radiotracer (123I) ß-carboxymethoxy-3-ß-(4-iodophenyl) tropane (CIT) might do a better job, detecting those patients who are thought to have PS, but turn out negative at follow-up.

The authors, based in Connecticut and New York, evaluated the effectiveness of (123I) ß-CIT and SPECT imaging in PS diagnoses, and shared their findings in the Archives of Neurology.

"Misdiagnosing other conditions as PS may lead to futile therapy with dopamine-replacing agents, often resulting in unnecessary adverse effects," according to lead author Dr. Danna Jennings from the Institute for Neurodegenerative Disorders in New Haven, CT. "In addition, significant resources are spent on CT or MRI of the brain, which are obtained to rule out other less likely etiologies of the parkinsonian symptoms" (Archives of Neurology, August 2004, Vol. 61:8, pp. 1224-1229).

Jenning's co-authors, Drs. Ken Marek and John Seibyl, are also from the New Haven institute. Co-author Dr. John Murphy is from Associated Neurologists in Danbury, CT. Finally, Shirley Eberly, Ph.D., and David Oakes, Ph.D., are from the department of biostatistics and computational biology at the University of Rochester in New York.

The researchers evaluated dopamine transporter (DAT) ligands using the radiotracer and SPECT as a diagnostic tool in patients with early parkinsonian symptoms suspected to have PS, but whose diagnoses were uncertain.

The study evaluated 35 patients (mean age of 66.8) with a diagnosis of suspected PS and were referred by 14 community neurologists over the course of a year. The subjects underwent (123I) ß-CIT and SPECT imaging within one month of their clinical evaluation. The research team noted that diagnoses in question included essential tremor, psychogenic parkinsonism, drug-induced parkinsonism, primary dystonia, and unspecified gait disorder.

"Parkinsonian syndrome was defined as PD and related striatal dopamine-deficient syndromes, including progressive supranuclear palsy, multiple system atrophy, striatal nigral degeneration, and corticobasalganglionic degeneration," the authors wrote.

The community neurologists and two movement disorder experts (MDEs) assigned a diagnosis of positive or negative PS prior to the imaging study. The neurologists' diagnosis at referral was positive PS in 30 of 35 patients; one MDE assigned positive PS in 31 of 35 cases, while the other MDE diagnosed positive PS in 25 of 35 patients.

A visual imaging diagnosis of positive or negative for PS was assigned to each SPECT image on the basis of a review of the pattern of striatal uptake of (123I) ß-CIT by a nuclear medicine expert and a technician who were blinded to the clinical data, the researchers reported. A standardized analysis method determined the specific nondisplaceable striatal uptake.

The researchers assigned a diagnosis of positive PS to patients who had a decrease in DAT density of greater than 30% on the basis of the quantitative imaging.

"There was disagreement among the community neurologists and the initial clinical diagnosis of one of the MDEs in 7 of 35 cases, with the diagnosis of the other MDE in 9 of 35, the visual imaging diagnosis in 12 of 35, and the quantitative imaging in 12 of 35," the authors wrote.

A six-month follow-up clinical diagnosis was assigned by an MDE blinded to the imaging data, which represented the gold standard diagnosis for the study, according to the researchers. The gold standard diagnosis found positive PS in 25 cases and negative PS in the other 10 cases.

When comparing the community neurologist’s diagnoses at referral with the gold standard diagnosis, the researchers found disagreement in 25.7% (9 of 35) of the cases. When comparing the visual imaging and quantitative imaging diagnoses with the gold standard, disagreement occurred in 8.6% (3 of 35) and 5.7% (2 of 35), respectively, of the cases.

The group noted an increase in diagnosis congruency between the clinical and imaging diagnoses at the six-month follow-up evaluation. This suggests that (123I) ß-CIT and SPECT imaging conducted at a baseline PS diagnosis can help determine positive or negative PS, according to the researchers.

Although substantial disagreement occurred between the DAT imaging diagnosis and the clinical diagnosis, the authors observed that this might be attributed to the cohort selected for the study.

"It should be emphasized that the population studied represents difficult-to-diagnose cases and does not represent all patients diagnosed with PS," they wrote.

By Jonathan S. Batchelor
AuntMinnie.com staff writer
October 12, 2004

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