COMPLEXITY OF VISUAL ANALYSIS OF PARKINSONIAN SYNDROMES
Parkinsonian syndromes correspond to a broad spectrum of dopaminergic and non-dopaminergic diseases, clinically defined by the same cardinal symptoms: rigidity, bradykinesia and tremor. In practice, neurodegenerative etiologies (idiopathic Parkinson's disease, Lewy body disease, multisystematic atrophy, corticobasal degeneration, and progressive supranuclear palsy), which are defined by histological alteration of the dopaminergic pathway, may be difficult to differentiate from non-dopaminergic parkinsonian syndromes (in which motor signs respond poorly or not at all to dopaminergic treatment). Molecular imaging of the dopamine active transporter in conventional scintigraphy (DAT SPECT) has shown its clinical added value in the diagnosis of such atypical syndromes.
For several years, 18F-DOPA PET imaging has been of increasing interest in clinical practice for the diagnostic evaluation of parkinsonian syndromes and, although less routinely used, it has several advantages over DAT SPECT (improved spatial resolution, reduced dosimetry and cost of the imaging procedure). However, visual interpretation methods in 18F-DOPA PET remain empirical, and international guidelines are modeled on those of DAT SPECT. A recent 18F-DOPA PET/CT imaging study described a characteristic schematic "rabbit" appearance of the striatum in 3D, modified exclusively in patients with parkinsonian syndromes. In practice, this striatal pattern can be instantly and easily observed on 3D reconstructions, without the need for any image post-processing. Despite its obvious simplicity, the relevance of this pattern in clinical practice remains unknown.
CONTRIBUTION OF 18F-DOPA TEP IMAGING OF THE RABBIT-SHAPED STRIATUM
In this study, the researchers compared the diagnostic performance of the rabbit-shaped scheme to the current standard procedure approved by the international nuclear imaging societies (EANM/SNMMI). 18F-DOPA PET images of 129 patients (65 Parkinson's and 64 controls) with 1-year clinical follow-up were independently reviewed by 5 experienced readers on the same imaging workstation, blinded to the final clinical diagnosis. Two visual methods were evaluated independently, within days or months of each other: the EANM/SNMMI approved criteria and the rabbit shape of the striatum, evaluated on 3D MIP (Maximum Intensity Projection) images. The 2 methods provided similar diagnostic performance, with no statistical difference in terms of accuracy, likelihood ratio, or predictive values. The rabbit shape reduced the discrepancies between the readers by 25%, while maintaining the same diagnostic performance.
The rabbit visual pattern assessed on 18F-DOPA MIP images appears to be at least comparable to the current EANM/SNMMI procedure for the assessment of parkinsonian syndromes in daily clinical practice, without the need for image postprocessing. Very encouraging, the results would however require further prospective multicenter studies to validate the clinical utility of such a pattern.
Contact: Florent Besson (florent.besson@universite-paris-saclay.fr)
EANM/SNMMI: European Association of Nuclear Medicine / Society of Nuclear Medicine and Molecular Imaging. SNMMI/EANM periodically sets new standards/guidelines for the practice of nuclear medicine to advance the science of this discipline and improve the quality of service to patients.
The striatum is a small deep subcortical brain structure involved in motor planning, decision making, motivation and reward-controlled learning.