Nigro-caudate dopaminergic deafferentation: a marker of REM sleep behavior disorder?

Forty-nine consecutive, drug naïve outpatients with de novo Parkinson's disease (PD) and 12 patients with idiopathic rapid eye movement sleep behavior disorder (iRBD) underwent clinical examination and dopamine transporter single photon emission computed tomography with [(123)I]-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)nortropane as a biomarker of nigro-striatal function. PD patients were grouped into rapid eye movement sleep behavior disorder (RBD) negative (PD-RBD-) and RBD positive (PD-RBD+). Repeated measures and univariate analysis of variance were used to compare dopaminergic and clinical impairment among groups. The variations of dopamine transporter-single photon emission computed tomography specific binding ratios (SBR) as a function of group belonging were significantly different (p = 0.0013) at caudate with respect to putamen level. Indeed, putamen SBR progressively decreased from iRBD to PD-RBD- and PD-RBD+ groups while caudate SBR were higher in PD-RBD- group than in PD-RBD+ and even than in iRBD group. Motor impairment was more severe in PD patients with RBD than in those without RBD. Our data suggest that a more severe nigro-caudate dopaminergic deafferentation is related to RBD, both in its idiopathic form and in PD patients.