Midbrain Energy Homeostasis Biomarker for Differential Diagnosis of Early-Stage Parkinson Disease: A 1 H and 31 P MRI Study

Background Whether phosphorus 31 (31P) MR spectroscopy outperforms or complements conventional hydrogen 1 (1H) MRI biomarkers in the differential diagnosis of early-stage Parkinson disease (PD) remains unclear. Purpose To evaluate 31P MR spectroscopy and its integration with conventional 1H MRI for discriminating early-stage PD from mimics. Materials and Methods This prospective study consecutively enrolled participants with early-stage PD, participants with PD mimics, and controls (November 2023 to October 2024). Participants underwent 31P MR spectroscopy for inorganic phosphate (Pi), phosphocreatine (PCr), and adenosine triphosphate (ATP); quantitative susceptibility mapping for iron; and neuromelanin-sensitive MRI. Intergroup imaging differences were assessed using multivariable general linear models, and partial correlations with clinical scores were analyzed. A penalized logistic regression classifier evaluated discrimination performance of energy metabolites, alone and combined with iron and/or neuromelanin. Results Seventy-two participants with early-stage PD (mean age, 60.1 years ± 6.8 SD; 44 male participants), 34 with PD mimics (mean age, 62.1 years ± 7.9; 18 male participants), and 46 controls (mean age, 56.3 years ± 9.6; 33 female controls) were included. Early-stage PD showed a decreased Pi/PCr ratio (mean, 0.47 95% CI: 0.44, 0.50 vs 0.57 95% CI: 0.52, 0.63) and an increased total ATP/Pi ratio (mean, 4.89 95% CI: 4.57, 5.24 vs 4.06 95% CI: 3.50, 4.68) in the left midbrain compared with participants with PD mimics (both Bonferroni-corrected P r = 0.42; 95% CI: 0.12, 0.69; P = .008) and autonomic symptom scores (r = 0.60; 95% CI: 0.34, 0.80; P P P = .04) in differentiating PD from mimics. There was no evidence that combining iron and/or neuromelanin improved AUC over energy metabolites alone (0.90 vs 0.90 with the addition of iron P > .99 vs 0.91 with the addition of neuromelanin P = .70 vs 0.93 with the addition of both P = .42). Conclusion 31P MR spectroscopy revealed disrupted midbrain energy homeostasis in early-stage PD and effectively helped differentiate it from mimics. © RSNA, 2026 Supplemental material is available for this article.