Psychophysiological and electrophysiological testing of olfactory and gustatory function in patients with multiple sclerosis

Abstract

The olfactory (OF) and gustatory function in multiple sclerosis (MS) patients and possible influencing variables of the disease, such as depression or fatigue, were determined. In an open prospective controlled clinical study 30 patients with MS and 30 healthy controls matched for age, sex and smoking-habits were investigated. With Mini Mental State Examination cognitive dysfunction was excluded, with Expanded Disability Status Scale the patient's ability to accomplish the tests was ensured. The severity of depression was measured with the self-reported Beck Depression Inventory. The orthonasal olfactory function was derived with olfactory event related potentials (OERP) and TDI-score (Threshold, Discrimination and Identification, Sniffin' Sticks). Retronasal olfactory function was tested with Taste-Powder-score, gustatory function with Taste-strip-score. There was a significant loss of olfactory function measured with TDI-score [12/30 (40%), p = 0.002] and gustatory function [5/23 (21.7%), p \ 0.001] in MS-patients, 23.8% (5/21) of MS-patients showed hyposmia with OERPs, significantly correlating with the TDI-score (p = 0.03). The Expanded Disability Status scale score inversely correlated with the TDI-score (p = 0.002). This study confirms the incidence of olfactory disorder in MS-patients and reveals a frequent gustatory deficit. The Identification subtest can be proposed as a marker of the OF in MS-patients: it includes complex cognitive tasks and may be influenced by depression and fatigue, which are common symptoms of MS. It inversely correlates with the disability status.

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…”

“…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.…”

“…In comparison to olfactory threshold abnormalities which appear restricted to the neuroepithelial compartment, the involvement of olfactory bulb/tract and cortex in RR and progressive MS could merely reflect more diffusely distributed pathology as is recognised with disease evolution. This might also explain why deficits in olfaction in MS have been linked to the extent of disability (as measured by the ambulatory-biased EDSS) 19 31 35 37 44 46 51 52. While the degree to which olfactory defects in MS relate to cognitive dysfunction, and depression remains an area of controversy,31 40 51 52 intriguingly, a contribution of olfactory bulb/tract pathology to cognitive problems and depressive symptoms warrants consideration based on mouse models where olfactory bulbectomy drives depressive behaviour and global cognitive dysfunction 70…”

Detection of Olfactory Dysfunction Using Olfactory Event Related Potentials in Young Patients with Multiple Sclerosis

“…The studies evaluating the relationship between MS and the three olfactory abilities used psychophysical tests [11], [17], [19]–[23], such as the Sniffin' Sticks Test [24], [25] and the University of Pennsylvania Smell Identification Test (UPSIT) [26]. However, the psychophysical tests of identification and discrimination require complex cognitive functions and high attention levels which could be compromised also in the early stage of MS [27], [28].…”

Olfactory and gustatory dysfunction in Myasthenia gravis: A study in Turkish patients

“…Odors binding to the olfactory receptor neurons trigger olfactory activity [8]. The processing of odors within the central nervous system includes the orbitofrontal cortex, the limbic system, insula and cerebellum, among other structures [9,10]. Gustatory fibers, on the other hand, reach the brain via the facial, glossopharyngeal, and vagal nerves.…”