Preclinical substantia nigra dysfunction in rapid eye movement sleep behaviour disorder

Objectives: Transcranial sonography (TCS) has been shown to reveal hyperechogenicity of the substantia nigra (SN) in people with Parkinson's disease and in approximately 10% of healthy subjects. It is hypothesized that SN hyperechogenicity in healthy subjects and patients with idiopathic rapid eye movement (REM) sleep behaviour disorder (iRBD) patients is a marker of vulnerability for Parkinson's disease. Methods: TCS and positron emission tomography (PET) with 6-[F-18] fluoro-meta-tyrosine (FMT), which can assess the level of the presynaptic dopaminergic nerve, were performed in 19 male patients with iRBD, mean age 66.4 (standard deviation [SD] 4.9) years, to assess nigrostriatal function, Results: Nine patients had pathological SN hyperechogenicity (mean age 66.8 [SD 3.9] years; 0.31 [SD 0.12] cm(2)) and 10 patients did not have SN hyperechogenicity (mean age 66.0 [SD 5.8] years; 0.11 [SD 0.06] cm(2)). FMT uptake at the putamen and caudate was significantly lower in iRBD patients with pathological SN hyperechogenicity compared with those without SN hyperechogenicity. However, no correlation was found between SN echogenicity and FMT uptake. This is in conflict with previous findings which showed that subjects with hyperechogenicity had lower FMT uptake in the striatum. Conclusion: Pathological hyperechogenic alterations in the SN in patients with iRBD may suggest the existence of preclinical SN dysfunction as determined by FMT-PET. (C) 2011 Elsevier B.V. All rights reserved.