MRI Study: Objective Olfactory Function and CNS Pathologies in Patients with Multiple Sclerosis

Abstract

Background: Multiple sclerosis (MS) is a chronic disease characterized by CNS lesions causing physical and cognitive impairment. Using psychophysical testing, an olfactory disorder is diagnosed in 15-38.5% of patients with MS. Olfactometry permits objective testing of the sensory nerve function. Methods: The study looked at 20 patients with MS. Clinical, olfactory (chemosensory evoked potentials), and MRI data (volume of the bulbus olfactorius (BO), olfactory brain (OB), lesions in the CNS) were analyzed. Results: 25 percent of patients were hyposmic, exhibiting higher OB lesion volumes and smaller bulb volumes. H₂S and CO₂ latencies and the BO volume (inversely) correlated with the volume and number of MS lesions of the olfactory brain in all patients. Patients with a smaller olfactory bulb volume exhibited longer H₂S latencies (p = 0.025). Conclusion: A relationship between olfactory bulb volume, olfactory brain lesion load, and objective olfactory function testing in MS patients was investigated in all patients. Our data shows that brain damage characteristic of MS, including reduced bulb volume, causes an increase in chemosensory potential latencies and an olfactory function deficit.

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

“…The extent of OEP disturbance in MS related to poor performance on the UPSIT score and to the extent of physical disability, as measured by Expanded Disability Status Score (EDSS), in the disease (see clinical association section below) 22 38. Other independent groups have corroborated these OEP findings in MS, adding further credence to physiological disturbance of these olfactory structures at some point in the clinical evolution of the disease 29 31 39…”

“…Through the measurement of olfactory bulb and tract volume, a Berlin-based group have repeatedly demonstrated reductions in these structures in MS compared with controls,37 39 49 and have shown that these changes relate to loss of smell and37 49 OEP disturbance (figure 1C) 39. Olfactory bulb volume and olfactory sulcus depth have also been shown to be inversely correlated with disease duration and attack frequency in MS 54.…”

“…OEPs are deranged in MS 22 29 31 38 39. In a cohort of 45 patients with MS and 47 controls, Hawkes et al found an increase in latency and a decrease in amplitude of the H 2 S (olfactory)-related OEP in MS compared with controls, suggesting demyelination and axonal loss within olfactory bulb/tract and/or olfactory brain as an element of MS pathology 22 38.…”

“…This seminal finding pointed to the olfactory brain as the main substrate of smell loss in MS. This view has been recently broadened to include a role for olfactory bulb pathology as an important contributor to smell loss in MS with lower mean olfactory bulb (bulbus olfactorius) volume observed in hyposmic compared with normosmic patients with MS (C; from Holinski et al 39 with permission).…”

“…Recent MRI studies have examined olfactory bulbs and tracts as possible contributors to olfactory disturbance in MS 37 39 49. Through the measurement of olfactory bulb and tract volume, a Berlin-based group have repeatedly demonstrated reductions in these structures in MS compared with controls,37 39 49 and have shown that these changes relate to loss of smell and37 49 OEP disturbance (figure 1C) 39.…”