Neuromelanin-sensitive MRI of the substantia nigra: An imaging biomarker to differentiate essential tremor from tremor-dominant Parkinson's disease

Introduction We aimed to evaluate whether neuromelanin-sensitive MRI (NM-MRI) features in the substantia nigra pars compacta (SNc) were of diagnostic value to differentiate untreated essential tremor (ET) from de novo tremor-dominant Parkinson's disease (PDT). Methods Eighteen untreated ET patients, 21 de novo PDT patients and 21 healthy control subjects were recruited. All the subjects underwent clinical examination, motor and cognitive evaluations, as well as NM-MRI. High signal intensity of the lateral, central and medial SNc subregions on NM-MRI were evaluated using the width, signal intensity (contrast-to-noise ratio, CNR) and visual analysis. Diagnostic test performance of SNc values was investigated by using receiver operating characteristic analysis and net reclassification improvement (NRI). Results The width and CNR values of the lateral and central SNc subregions in PDT were significantly decreased compared with those in ET and control group. Using visual analysis, the total visual score of all SNc subregions was significantly reduced in PDT when compared with ET and control group. The width of the lateral SNc subregion allowed the best differentiation between ET and PDT, and visual analysis also showed good diagnostic value. NRI result indicated that visual analysis and the width of the lateral SNc subregion had the same diagnostic power. Conclusions The neuromelanin changes of SNc in ET and PDT follow the different patterns. Both the measurements and visual analysis of SNc on NM-MRI provide high diagnostic accuracy for differentiating ET from PDT subtype. NM-MRI is a potential tool in diagnostic work-up of tremor disorders.