Smell and taste in cervical dystonia

Abstract

The pathophysiology of cervical dystonia is not completely understood. Current concepts of the pathophysiology propose that it is a network disorder involving the basal ganglia, cerebellum and sensorimotor cortex. These structures are primarily concerned with sensorimotor control but are also involved in non-motor functioning such as the processing of information related to the chemical senses. This overlap lets us hypothesize a link between cervical dystonia and altered sense of smell and taste. To prove this hypothesis and to contribute to the better understanding of cervical dystonia, we assessed olfactory and gustatory functioning in 40 adults with idiopathic cervical dystonia and 40 healthy controls. The Sniffin Sticks were used to assess odor threshold, discrimination and identification. Furthermore, the Taste Strips were applied to assess the combined taste score. Motor and non-motor deficits of cervical dystonia including neuropsychological and psychiatric alterations were assessed as cofactors for regression analyses. We found that cervical dystonia subjects had lower scores than healthy controls for odor threshold (5.8 ± 2.4 versus 8.0 ± 3.2; p = 0.001), odor identification (11.7 ± 2.3 versus 13.1 ± 1.3; p = 0.001) and the combined taste score (9.5 ± 2.2 versus 11.7 ± 2.7; p < 0.001), while no difference was found in odor discrimination (12.0 ± 2.5 versus 12.9 ± 1.8; p = 0.097). Regression analysis suggests that age is the main predictor for olfactory decline in subjects with cervical dystonia. Moreover, performance in the Montreal Cognitive Assessment is a predictor for gustatory decline in cervical dystonia subjects. Findings propose that cervical dystonia is associated with diminished olfactory and gustatory functioning.

Olfaction as a Marker for Dystonia: Background, Current State and Directions

“…Clinical parameters, such as the degree of cervical dystonia, did not predict olfactory decline. Non-motor manifestations of dystonia, such as cognitive and psychiatric alterations, which potentially impact the performance of olfactory tests [ 161 , 164 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 175 , 176 , 177 , 178 , 179 ], were not assessed as co-factors in this study.…”

“…To comprehensively assess the chemical sense in dystonia, a more recent study appraised the sense of smell, as well as the sense of taste in subjects with cervical dystonia, which was compared to carefully matched healthy controls ( Table 1 ) [ 161 ]. Moreover, cognitive and psychiatric alterations as non-motor manifestations of dystonia were assessed by the use of an extensive test battery.…”

“…Moreover, cognitive and psychiatric alterations as non-motor manifestations of dystonia were assessed by the use of an extensive test battery. For the best possible comparison of the two groups and to exclude other causes that could impact the chemical senses as suggested by a consensus panel [ 47 ], the researchers applied an extensive list of exclusion criteria [ 161 ]. Dystonia subjects on treatment with botulinum toxin were assessed 3 months after their last injections, when the effects of botulinum toxin treatment had wasted.…”

“…It is possibly too early to define olfaction as a trait marker for dystonia. However, two independent studies revealed diminished odor threshold and diminished odor identification as the pattern of olfactory decline in subjects with cervical dystonia [ 160 , 161 ]. Findings are possibly related to the involvement of the basal ganglia, cerebellum, and sensorimotor cortex in both the pathophysiology of dystonia and the processing of olfactory information.…”

Smell and taste in idiopathic blepharospasm

“…Because of the anatomical overlap of structures involved in the pathophysiology of idiopathic BSP and the chemical senses, an impairment of the sense of smell and taste may be found in subjects with idiopathic BSP. This idea is supported by diminished chemical senses in subjects with cervical dystonia (CD) (Marek et al 2018 ; Herr et al 2020 ), where alterations in the sensorimotor control network are also found (Jinnah et al 2013 , 2017 ). Although largely overlooked, the chemical senses fulfill fundamental aspects important for daily life (Croy et al 2014 ; Doty 2019 ).…”