Preclinical substantia nigra dysfunction in rapid eye movement sleep behaviour disorder

Area of Science:

• Neurology
• Neuroimaging
• Sleep Medicine

Background:

• Transcranial sonography (TCS) detects substantia nigra (SN) hyperechogenicity in Parkinson's disease and some healthy subjects.
• SN hyperechogenicity is hypothesized as a potential marker for Parkinson's disease vulnerability in healthy individuals and idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) patients.

Purpose of the Study:

• To investigate the association between SN hyperechogenicity and nigrostriatal function in iRBD patients.
• To assess presynaptic dopaminergic nerve levels using positron emission tomography (PET) with 6-[(18)F] fluoro-meta-tyrosine (FMT).

Main Methods:

• 19 male iRBD patients underwent TCS and FMT-PET scans.
• Nigrostriatal function was assessed by measuring FMT uptake in the putamen and caudate nucleus.
• Patients were categorized based on the presence or absence of pathological SN hyperechogenicity.

Main Results:

• Nine patients exhibited pathological SN hyperechogenicity, while 10 did not.
• FMT uptake was significantly lower in iRBD patients with pathological SN hyperechogenicity compared to those without.
• No direct correlation was found between SN echogenicity and FMT uptake, conflicting with some prior studies.

Conclusions:

• Pathological SN hyperechogenic alterations in iRBD patients may indicate preclinical substantia nigra dysfunction.
• FMT-PET imaging supports the hypothesis that SN hyperechogenicity is linked to early dopaminergic deficits in iRBD.