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

Thorsten Herr,Bernhard Lehnert,Barbara Caspers,Marcus Vollmer,Carsten Willert,Andrea Stenner,Birgitt Veit,Jan-Uwe Mueller,Robert Fleischmann,Martin Kronenbuerger,Julie Gamain

doi:10.3390/brainsci10100727

Abstract

Dystonia is a heterogeneous group of hyperkinetic movement disorders. The unifying descriptor of dystonia is the motor manifestation, characterized by continuous or intermittent contractions of muscles that cause abnormal movements and postures. Additionally, there are psychiatric, cognitive, and sensory alterations that are possible or putative non-motor manifestations of dystonia. The pathophysiology of dystonia is incompletely understood. A better understanding of dystonia pathophysiology is highly relevant in the amelioration of significant disability associated with motor and non-motor manifestations of dystonia. Recently, diminished olfaction was found to be a potential non-motor manifestation that may worsen the situation of subjects with dystonia. Yet, this finding may also shed light into dystonia pathophysiology and yield novel treatment options. This article aims to provide background information on dystonia and the current understanding of its pathophysiology, including the key structures involved, namely, the basal ganglia, cerebellum, and sensorimotor cortex. Additionally, involvement of these structures in the chemical senses are reviewed to provide an overview on how olfactory (and gustatory) deficits may occur in dystonia. Finally, we describe the present findings on altered chemical senses in dystonia and discuss directions of research on olfactory dysfunction as a marker in dystonia.

Highlights

In clinical neuroscience, olfactory decline is typically associated with sinunasal disease, head trauma, infections of the upper respiratory tract, dementing illnesses such as Alzheimer’s disease, and movement disorders such as Parkinson’s disease [1,2,3]
Standard neuroimaging such as computed tomography (CT) and magnetic resonance imaging (MRI) are typically normal in subjects with primary dystonia [69,70,71,72]
Lesions in secondary dystonia were most commonly located in a network including the basal ganglia, cerebellum, and sensorimotor cortex [73,75,76,77,78]

Summary

Introduction

Olfactory decline is typically associated with sinunasal disease, head trauma, infections of the upper respiratory tract, dementing illnesses such as Alzheimer’s disease, and movement disorders such as Parkinson’s disease [1,2,3]. The most common form of dystonia encountered in adult neurology is focal dystonia [4]. Within the group of focal dystonia, cervical dystonia is the most prevalent type, being characterized by a sustained or jerky position of the neck [4,6]. There are numerous non-motor alterations in the different forms of dystonia [8,9]. These include psychiatric alterations (such as depression and anxiety), mild cognitive deficits (such as deficits in executive functioning, verbal fluency, and memory), and changes in the sensory domain (such as pain, kinesthetic sensation, impaired somatosensory discrimination, and alleviating maneuvers) [8,9]

Objectives

Results

Conclusion