MRI Assessment of Nigrosome in Parkinson's Disease: Is it Currently a Valuable Tool in Clinical Practice?

BACKGROUND: Dopaminergic neuron loss in the substantia nigra, particularly the nigrosomes, characterizes Parkinson's disease (PD). Nigrosome-1 absence on MRI has emerged as a potential PD biomarker. OBJECTIVES: Assess the diagnostic accuracy of nigrosome-1 detection for differentiating PD from essential tremor (ET) in clinical practice. METHODS: Movement disorder neurologists without nigrosome evaluation experience, randomized into receiving or not training, assessed 3 Tesla MRIs from PD and ET patients. PD was defined by absence of at least one nigrosome. Diagnostic accuracy measures and inter-rater agreement were calculated. RESULTS: Seventy-two MRIs were included (43 PD, 29 ET). Mean sensitivity, specificity, and accuracy were 78.2% (95% confidence interval: 71.2-85.3), 56.7% (50.0-64.0), 69.5% (65.3-73.9), without significant differences between groups. Specificity (P = 0.002) and accuracy (P = 0.029) increased with rating experience. CONCLUSIONS: Nigrosome assessment in routine MRI by inexperienced raters showed limited diagnostic performance, yet may improve with optimized protocols and continued practice.