Botulinum Toxin Effects on Sensorimotor Integration in Focal Dystonias

Maria Ilenia De Bartolo,Daniele Belvisi,Viola Baione,Gina Ferrazzano,Giovanni Fabbrini,Alfredo Berardelli,Antonella Conte,Nicoletta Manzo

doi:10.3390/toxins12050277

Maria Ilenia De Bartolo, Daniele Belvisi + Show 6 more

Open Access

https://doi.org/10.3390/toxins12050277

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Abstract

(1) Background: In dystonia, the somatosensory temporal discrimination threshold (STDT) is abnormally increased at rest and higher and longer-lasting during movement execution in comparison with healthy subjects (HS), suggesting an abnormal sensorimotor integration. These abnormalities are thought to depend on abnormal proprioceptive input coming from dystonic muscles. Since Botulinum toxin-A (BT-A) reduces proprioceptive input in the injected muscles, our study investigated the effects of BT-A on STDT tested at rest and during voluntary movement execution in patients with focal dystonia. (2) Methods: We enrolled 35 patients with focal dystonia: 14 patients with cervical dystonia (CD), 11 patients with blepharospasm (BSP), and 10 patients with focal hand dystonia (FHD); and 12 age-matched HS. STDT tested by delivering paired stimuli was measured in all subjects at rest and during index finger abductions. (3) Results: Patients with dystonia had higher STDT values at rest and during movement execution than HS. While BT-A did not modify STDT at rest, it reduced the abnormal values of STDT during movement in CD and FHD patients, but not in BSP patients. (4) Conclusions: BT-A improved abnormal sensorimotor integration in CD and FHD, most likely by decreasing the overflow of proprioceptive signaling from muscle dystonic activity to the thalamus.

Highlights

Temporal discrimination can be tested in humans with the somatosensory temporal discrimination threshold (STDT) technique, which assesses the interval needed to recognize a pair of stimuli as separate in time [1]
We found that Botulinum toxin-A (BT-A) did not modify abnormal STDT values tested at rest in cervical dystonia (CD) patients [15]
Before BT-A, STDT values tested at rest were higher in dystonia patients than in healthy subjects (HS) (p = 0.01)

Summary

Introduction

Temporal discrimination can be tested in humans with the somatosensory temporal discrimination threshold (STDT) technique, which assesses the interval needed to recognize a pair of stimuli as separate in time [1]. STDT is decoded by a cortical-subcortical loop involving sensory motor cortex (S1) and the basal ganglia [2,3]. In HS, STDT values increase when tested during voluntary movement execution and return to normal after the end of the movement. The increase in STDT during movement execution reflects mechanisms of sensorimotor integration, the process of gating tactile input during movement. This gating is necessary in order to prioritize proprioceptive input. Several studies have concluded that sensorimotor integration between tactile stimuli and voluntary movement is influenced by central mechanisms, including thalamo-basal ganglia interplay [4,5].

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