Basic and long-term monitoring of changes in dopamine transporter availability (DAT) can help identify patients with idiopathic sleep behavior disorder (iRBD) with rapid eye movements (iRBD) who are at high risk of converting to neurodegenerative diseases, according to published study results in neurology .
Previous studies have shown that iRBD is a powerful prodromal marker for Parkinson’s disease (PD). The study researchers therefore tried to investigate the relationship between longitudinal changes in DAT availability and prodromal markers in iRBD.
In this prospective study, South Korean researchers enrolled 31 patients with drug-naive Parkinson’s disease, 39 patients with iRBD and 19 healthy patients as controls. They recorded age, gender, and duration of RBD at baseline. Participants underwent olfactory and neuropsychological assessment, and study researchers rated their motor and non-motor symptoms of Parkinson’s disease using the Movement Disorders Society’s revised unified PD rating scale. Participants also received an F-FP-CIT-PET scan every 2 years. In addition, the study’s researchers assessed longitudinal changes in DAT availability using a principal component analysis of tracer uptake in the bilateral striatum.
At the start of the study, no differences between the groups with regard to gender and age were found. In the patients with iRBD, 10 patients developed neurodegenerative disease during a mean follow-up period of 3.22 years. The calculated phenoconversion rates after 2 and 5 years were 14.7% and 36.6%, respectively. The estimated annual conversion rate for this cohort was 7.32%.
The DAT pattern of patients with iRBD and baseline hyposmia, constipation, and mild Parkinson’s signs was distributed across a PD pattern that differentiated them from patients in the healthy control group. During the follow-up examination, the DAT pattern moved towards the PD pattern in some patients with iRBD in the healthy control pattern over time. In these patients, baseline hyposmia was the only biomarker associated with this change.
DAT baseline PD pattern predicted about 58 percent of disease converters (hazard ratio) [HR]4.95; 95% CI, 1.16-21.08). A combination of hyposmia and baseline PD patterns from DAT predicted up to 67 percent of conversion (HR 7.89; 95% CI 1.85-33.69). A significantly lower percentage of hyposmia was seen in non-converters (29.4%) who completed the follow-up study compared to converters (P = 0.0044).
According to the study’s researchers, the results of this study suggest that “hyposmia should be viewed as a unique clinical marker that reflects the baseline status of neurodegeneration and the prediction of an impending rapid DAT decline and phenoconversion to neurodegenerative diseases in patients with iRBD” .
Shin JH, Lee JY, Kim YK et al. Longitudinal change in the availability of dopamine transporters in idiopathic REM sleep behavior disorder. Neurology. Published online on September 28, 2020. doi: 10.1212 / WNL.0000000000010942