Aberrancies of Brain Network Structures in Patients with Anosmia

Patients with anosmia exhibit structural and functional brain abnormalities. The present study explored changes in brain white matter (WM) in non-neurodegenerative anosmia using diffusion-tensor-based network analysis. Twenty patients with anosmia and sixteen healthy controls were recruited in the cross-sectional, case-control study. Participants underwent olfactory tests (orthonasal and retronasal), neuropsychological assessment (cognitive function and depressive symptoms) and diffusion tensor imaging measurement. Tract-Based Spatial Statistics, graph theoretical analysis and Network-Based Statistics were used to explore the white matter. There was no significant difference in fractional anisotropy (FA) between patients and controls. In global network topological properties comparisons, patients exhibited higher gamma and lambda levels than controls, and both groups satisfied the criteria of small-world (sigma > 1). In local network topological properties, patients had reduced betweenness, degree and efficiency (global and local), as well as increased shortest path length and cluster coefficient in olfactory-related brain areas (anterior cingulum, lenticular nucleus, putamen, hippocampus, amygdala, caudate nucleus, orbito-frontal gyrus). Olfactory threshold scores and the retronasal score were negatively correlated with gamma and lambda, and the retronasal score was positively correlated with FA values in certain WM tracts, i.e. middle cerebellar peduncle, right inferior cerebellar peduncle, left inferior cerebellar peduncle, right cerebral peduncle, left cerebral peduncle, left cingulum (cingulate gyrus), right cingulum (hippocampus), superior fronto-occipital fasciculus, and, left tapetum. Patients with anosmia demonstrated relevant WM network dysfunction though their structural integrity remained intact. Their retronasal olfaction deficits revealed to be more strongly associated with WM alterations compared with orthonasal olfactory scores.