Discordance Between Striatal Dopaminergic Imaging and Motor Performances in REM Sleep Behavior Disorder

Area of Science:

• Neurology
• Neuroscience
• Sleep Medicine

Background:

• Idiopathic REM sleep behavior disorder (iRBD) is an early indicator of synucleinopathy.
• Nigrostriatal dopaminergic dysfunction is typically linked to iRBD motor symptoms.
• Alternative pathological mechanisms in iRBD require investigation.

Purpose of the Study:

• To investigate discordance between motor function and nigrostriatal uptake in iRBD patients.
• To characterize iRBD patients exhibiting discrepancies between motor testing and DaT-SPECT results.

Main Methods:

• A multicenter study involving 108 iRBD patients confirmed by polysomnography.
• Utilized [123I]-Ioflupane SPECT (DaT-SPECT) and quantitative motor testing.
• Categorized participants into four groups based on motor and DaT-SPECT findings, with prospective follow-up.

Main Results:

• 40% of iRBD patients showed discordance between motor testing and DaT-SPECT.
• The motor slowing/DaT normal group exhibited poorer cognitive scores (MoCA) and higher rates of mild cognitive impairment (MCI).
• This group also presented with more severe autonomic dysfunction and a 15% phenoconversion rate to Parkinson's disease or dementia with Lewy bodies.

Conclusions:

• Motor alterations and nigrostriatal uptake are frequently discordant in iRBD.
• Cognitive and autonomic dysfunction in the motor slowing/DaT normal group suggests a distinct, potentially diffuse, disease progression pattern.