Date Published: January 20, 2017
Publisher: Public Library of Science
Author(s): Florian Cornelius Uecker, Heidi Olze, Hagen Kunte, Christian Gerz, Önder Göktas, Lutz Harms, Felix Alexander Schmidt, Fernando de Castro.
The aim of the study was to investigate changes of the olfactory and gustatory capacity in patients with multiple sclerosis (MS).
20 MS patients were tested longitudinally for 3 years after initial testing. The Threshold Discrimination Identification test (TDI) was used for subjective olfactometry. Objective olfactometry was performed by registering olfactory evoked potentials (OEP) by EEG. The Taste Strip Test (TST) was used for gustatory testing.
45% of the patients showed olfactory dysfunction in the follow-up TDI test and 50% showed delayed OEP´s. 20% of the patients showed gustatory dysfunction on follow-up visit. The patients showed mild disease activity with 0,3 ± 0,5 relapses over the testing period and no significant change of their olfactory and gustatory capacity. The olfactory capacity for the discrimination of odors correlated inversely with the number of relapses (r = -0.5, p ≤ 0.05). The patients were aware of their olfactory deficit.
Olfactory and gustatory dysfunction is a symptom in MS patients and may be a useful parameter to estimate disease progression in MS patients. As the discrimination of odors is processed in higher central regions of the central nervous system (CNS), the results suggest that olfactory dysfunction could be due to CNS damage.
Multiple Sclerosis (MS) is a chronic inflammatory disease affecting the CNS and typically follows a relapsing-remitting disease course (RRMS). Approximately 15% of all MS patients initially present with a primary progressive disease course (PPMS) characterized by constantly increasing physical disability without recovery. The neurological symptoms vary depending on the region of the brain that is affected by MS lesions [1,2]. Olfactory dysfunction mainly occurs with Alzheimer´s and Parkinson´s disease and less frequently with other neurodegenerative diseases [3,4]. Furthermore olfactory dysfunction often presents as a first symptom of Parkinson´s disease, occurring around 4–6 years before motor disorders begin [5,6]. Detecting olfactory disorders is becoming increasingly important in the research of neurological diseases . A dysfunction in the olfactory sense may have a great impact on quality of life .
We reported olfactory dysfunction in 45% of the longitudinally tested MS patients. Our results conform with previous studies, which reported olfactory dysfunction at rates of 11%–41% [7–10]. The olfactory capacity might have varied as different smell tests, such as the TDI test, the University of Pennsylvania Smell Identification Test (UPSIT) and Brief Smell Identification Test (B-SIT) were applied in the previous studies. Most of these studies grouped MS patients with relapsing remitting disease course and chronic progressive disease course together [7–13]. Interestingly, the olfactory and gustatory capacity of the MS patients remained stable during the longitudinal testing period in our study. The grade of physical disability expressed in the EDSS score also didn´t increase. These findings might be due to disease-modifying therapy that 70% of the patients were receiving. 75% of the patients with a gustatory dysfunction were also hyposmic. On a cortical level, the olfactory and the gustatory system intersect, in the insular cortex, the orbitofrontal cortex and the amygdala . Olfactory stimuli are linked with gustatory information, delivered to the anterior insula (multimodal integration), which might explain these results.