Abstract
The pathophysiology of blepharospasm is incompletely understood. Current concepts suggest that blepharospasm is a network disorder, involving basal ganglia, thalamus, cortex, and, possibly, the cerebellum. Tracing, imaging, and clinical studies revealed that these structures are also concerned with olfaction and taste. Because of this anatomical overlap, dysfunction of the chemical senses in blepharospasm is expected. Injections of botulinum toxin into the eyelid muscles are the first-line treatment of blepharospasm. Yet, the effects of botulinum toxin on the chemical senses have not been systematically assessed. To contribute to a better understanding of blepharospasm, olfactory and gustatory abilities were assessed in 17 subjects with blepharospasm and 17 age-/sex-matched healthy controls. Sniffin Sticks were used to assess odor threshold, odor discrimination, and odor identification. Results of these three Sniffin Sticks subtests were added to the composite olfactory score. The Taste Strips were applied to assess taste. In an adjacent study, we assessed the sense of smell and taste in eight subjects with blepharospasm before and 4 weeks after botulinum toxin treatment. Subjects with blepharospasm had significantly lower (= worse) scores for odor threshold and for the composite olfactory score than healthy controls, while odor discrimination, odor identification, and the composite taste score were not different between groups. The adjacent study revealed that botulinum toxin did not impact the chemical senses. In this study, subjects with blepharospasm had a lower (= worse) odor threshold than healthy controls. As olfaction is important in daily life, findings justify further research of olfaction in blepharospasm.
Highlights
Blepharospasm (BSP) is a dystonia subtype that is characterized by stereotyped, bilateral, and synchronous spasms of the orbicularis oculi muscle in combination with sensory tricks and increased blinking (Defazio et al 2017)
Healthy controls were matched for age, sex, education, and handedness of the subjects with idiopathic BSP
Two subjects with idiopathic BSP had a slight action tremor of the hands consistent with tremor associated with dystonia (Bhatia et al 2018)
Summary
Blepharospasm (BSP) is a dystonia subtype that is characterized by stereotyped, bilateral, and synchronous spasms of the orbicularis oculi muscle in combination with sensory tricks and increased blinking (Defazio et al 2017). Subjects with BSP may be functionally blind and unable to live a normal life due to spasms of the eyelid muscles (Valls-Sole and Defazio 2016). Sensory (such as dry eye and photophobia), psychiatric (such as depression and anxiety), and cognitive alterations (such as memory and executive function) are possible or putative non-motor deficits of BSP which negatively impact the quality of life (Ferrazzano et al 2019; Girach et al 2019). BSP may present secondary to a different illness, such as focal lesion in the brain, or in combination with other dystonias such as oro-mandibular dystonia (Albanese et al 2013). Being the most common cranial dystonia and the second most common focal
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