Olfactory dysfunction and extent of white matter abnormalities in multiple sclerosis: a clinical and MR study

The relative contribution to the olfactory dysfunction of the lesions in the specific brain regions involved in olfaction compared with the lesions scattered all over the rest of the brain has not been fully clarified yet in patients with multiple sclerosis (MS). The concurrent use of Magnetic Resonance Imaging (MRI) and a standardized test of odor identification ability now permits to study the relation between smell loss and the extent of white matter abnormalities.

We tested the olfactory function of 40 patients with definite MS and of 40 age-sex- and smoking-habit-matched healthy controls by using the Cross Cultural Smell Identification Test. We measured also the lesion load on T2-weighted images in the inferior-frontal and temporal lobes and in the rest of the brain in MS patients. Therefore, we tried to correlate measures of lesion load and smell test scores.

A robust correlation was demonstrated between MR measures of lesion load in the white matter of the olfactory brain region and smell loss (r=-0. 739, P<0.0001). A significant relationship has been found even after taking potential confounding factors, such as sex, age, disease duration, disability, anxiety and depression, into account (r=-0.90, P<0.0001).

Our findings show, in MS patients with stable neurological impairment and no recent disease exacerbation, a correlation between smell loss and the lesion load in the regions of the brain involved in olfaction and support the theory that the extent and severity of MRI abnormalities in specific brain regions are related to the presence of selective neurologic and neuropsychologic impairment.