title: Olfactory impairment in Parkinson's disease and white matter abnormalities in central olfactory areas: A voxel-based diffusion tensor imaging study.
abstract: Olfactory dysfunction is known to occur before the appearance of the classical motor signs in Parkinson's disease (PD) and diffusion tensor imaging (DTI) studies in PD have reported fractional anisotropy (FA) reductions in the early disease stages. We aimed to investigate the relationship between olfactory dysfunction and white matter (WM) FA of central olfactory areas in early PD. Twenty-four patients at Hoehn and Yahr stages I and II and 24 healthy controls matched by age, gender and years of education participated in this study. DTI was acquired at a 3 Tesla scanner and odor identification was assessed using the University of Pennsylvania Smell Identification Test (UPSIT). We performed FA voxelwise group comparisons in the central olfactory structures using tract-based spatial statistics (TBSS) and correlation analyses between FA values in these central olfactory areas and UPSIT scores. Patients with severe microsmia (UPSIT between 19 and 25) and anosmia (UPSIT lower or equal to 18) had lower FA values than PD patients with mild/moderate or no olfactory dysfunction (UPSIT between 26 and 40) and healthy controls in the WM adjacent to gyrus rectus. In addition, patients with anosmia had reduced FA in the WM surrounding primary olfactory areas in comparison with healthy controls. FA values in the WM adjacent to primary olfactory cortex and right gyrus rectus correlated with UPSIT scores in the PD group. This study demonstrates, for the first time, that microstructural WM reductions are present in the central olfactory system of early stage PD patients and that these reductions are associated with reduced ability to smell.
authors.affiliation: Centro de Investigación en Red de Enfermedades Neurodegenerativas (CIBERNED), Hospital Clínic de Barcelona, Barcelona, Spain.
authors.forename: Naroa
authors.initials: N
authors.lastname: Ibarretxe-Bilbao
authors.forename: Carme
authors.initials: C
authors.lastname: Junque
authors.forename: Maria-Jose
authors.initials: MJ
authors.lastname: Marti
authors.forename: Francesc
authors.initials: F
authors.lastname: Valldeoriola
authors.forename: Pere
authors.initials: P
authors.lastname: Vendrell
authors.forename: Nuria
authors.initials: N
authors.lastname: Bargallo
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Zarei
authors.forename: Eduardo
authors.initials: E
authors.lastname: Tolosa
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001931:Brain Mapping; D056324:Diffusion Tensor Imaging; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D000857:Olfaction Disorders / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D009833:Olfactory Pathways / Q000473:pathology / Q000503:physiopathology*; D010300:Parkinson Disease / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D012044:Regression Analysis; D012903:Smell