Occipital hypometabolism is a risk factor for conversion to Parkinson's disease in isolated REM sleep behaviour disorder

PurposeIsolated REM sleep behaviour disorder (iRBD) patients are at high risk of developing clinical syndromes of the alpha-synuclein spectrum. Progression markers are needed to determine the neurodegenerative changes and to predict their conversion. Brain imaging with F-18-FDG PET in iRBD is promising, but longitudinal studies are scarce. We investigated the regional brain changes in iRBD over time, related to phenoconversion.MethodsTwenty iRBD patients underwent two consecutive F-18-FDG PET brain scans and clinical assessments (3.7 +/- 0.6 years apart). Seventeen patients also underwent I-123-MIBG and I-123-FP-CIT SPECT scans at baseline. Four subjects phenoconverted to Parkinson's disease (PD) during follow-up. F-18-FDG PET scans were compared to controls with a voxel-wise single-subject procedure. The relationship between regional brain changes in metabolism and PD-related pattern scores (PDRP) was investigated.ResultsIndividual hypometabolism t-maps revealed three scenarios: (1) normal F-18-FDG PET scans at baseline and follow-up (N = 10); (2) normal scans at baseline but occipital or occipito-parietal hypometabolism at follow-up (N = 4); (3) occipital hypometabolism at baseline and follow-up (N = 6). All patients in the last group had pathological I-123-MIBG and I-123-FP-CIT SPECT. iRBD converters (N = 4) showed occipital hypometabolism at baseline (third scenario). At the group level, hypometabolism in the frontal and occipito-parietal regions and hypermetabolism in the cerebellum and limbic regions were progressive over time. PDRP z-scores increased over time (0.54 +/- 0.36 per year). PDRP expression was driven by occipital hypometabolism and cerebellar hypermetabolism.ConclusionsOur results suggest that occipital hypometabolism at baseline in iRBD implies a short-term conversion to PD. This might help in stratification strategies for disease-modifying trials.

Automated summary

A study investigated the regional brain changes in isolated REM sleep behavior disorder (iRBD) patients over time and their relationship to phenoconversion. The findings suggest that occipital hypometabolism at baseline in iRBD implies a short-term conversion to Parkinson's disease (PD).