Olfactory function in patients with multiple sclerosis: A diffusion tensor imaging study

Back on the scent: the olfactory system in CNS demyelinating diseases

“…In a similar vein, relapses negatively impact olfactory function, again with threshold disturbance being preferentially affected 41. With disease evolution, olfactory impairment appears to increasingly affect other olfactory domains, namely identification and/or discrimination 19 35 41 44 49…”

“…Around that time, an experimental report on human postmortem tissue identified a paucity of myelin basic protein in the olfactory bulb/tract,24 suggesting decreased likelihood of these CNS structures being subject to immune attack in MS, adding further support to this clinical finding. While a report in 1977 by Pinching28 once again identified olfactory disturbance in patients with MS and challenged the claim that there was a paucity of myelin within the bulb/tract, it was only from the late 1980s that momentum gathered in the investigation of loss of smell in MS. To date, a total of 30 studies on olfactory function in MS and other demyelinating disease have been published 19 22–24 27–53. The message that smell loss not only occurs in MS, but is common is now clear (see online supplementary table S1).…”

“…Not only is olfactory loss more common, it has been shown to be more severe in progressive and more advanced disease 19 35 37 41 44 47 49. A common theme across studies in patients with MS with progressive disease is impairment of olfactory discrimination and identification,19 35 44 49 similar to that seen in late RRMS 41 42 44. The shift in the nature of olfactory disturbance between early and late disease stages raises the question as to whether different olfactory structures are affected at different disease stages.…”

Tract-based spatial statistics of the olfactory brain in patients with multiple sclerosis

“…The other tasks, threshold (T) and discrimination (D) of different odours, might involve more peripheral parts of the olfactory system, and the subscores may be independent. Our previous study indicated that FA values of T2-visible lesions in the olfactory brain correlate with an impaired identification function [38]. However, in the current study we labelled the entire olfactory brain as a seed point for assessing the outgoing number of streamlines, including T2-visible and potential non-visible white matter abnormalities as well and compared to a group of healthy controls.…”

Olfactory dysfunction as a marker of multiple sclerosis progression

“…This could be explained by smell threshold being part of the more peripheral regions of the olfactory system while the ability to discriminate and identify odors are attributed to several damaged areas of the brain. When analyzing demyelinating plaques in brain MRI of MS patients [2][3][4][5] , the inferior frontal-and temporal-lobe regions, which are involved in olfaction, had a negative relation with smell dysfunction. Considering other brain regions not concerned to olfaction, the number of plaques did not have such relation.…”