Loss of Substantia Nigra Hyperintensity at 3.0-T MR Imaging in Idiopathic REM Sleep Behavior Disorder: Comparison with I-123-FP-CIT SPECT

Purpose: To examine whether the loss of nigral hyperintensity (NH) on 3.0-T susceptibility-weighted (SW) magnetic resonance (MR) images can help identify high synucleinopathy risk in patients with idiopathic rapid eye movement sleep behavior disorder (iRBD). Materials and Methods: Between March 2014 and April 2015, 18 consecutively recruited patients with iRBD were evaluated with 3.0-T SW imaging and iodine 123-2b-carbomethoxy-3b-(4iodophenyl)- N-(3-fluoropropyl)-nortropane (I-123-FP-CIT) single photon emission computed tomography and compared with 18 healthy subjects and 18 patients with Parkinson disease (PD). Two readers blinded to clinical diagnosis independently assessed the images. I-123-FP-CIT uptake ratios were compared by using the Kruskal-Wallis test, and intra-and interobserver agreements were assessed with the Cohen k. The synucleinopathy conversion according to NH status was evaluated in patients with iRBD after follow-up. Results: NH was intact in seven patients with iRBD and lost in 11. The I-123-FP-CIT uptake ratios were comparable between those with intact NH (mean, 3.22 6 0.47) and healthy subjects (mean, 3.37 6 0.47) (P =.495). The I-123-FPCIT uptake ratios in the 11 patients with iRBD and NH loss (mean, 2.48 +/- 0.44) were significantly lower than those in healthy subjects (mean, 3.37 +/- 0.47; P<.001) but higher than those in patients with PD (mean, 1.80 6 0.33; P<.001). The intra-and interobserver agreements were excellent (k. 0.9). Five patients with iRBD and NH loss developed symptoms of parkinsonism or dementia 18 months after neuroimaging. Conclusion: NH loss at 3.0-T SW imaging may be a promising marker for short-term synucleinopathy risk in iRBD.