Objective: In this study, we aimed to assess the biomechanical components underlying the postural alterations characteristic of CD. In addition, we investigated the effects of BoNT-A.

Background: Cervical dystonia (CD) is the most common focal dystonia and is primarily treated with botulinum toxin injections¹. However, its clinical assessment relies on semiquantitative scales such as the TWSTRS, lacking objective measures to reliably evaluate treatment response². Owing to the absence of biomarkers able to objectively assess muscle tone, the pathophysiology of muscle alterations in CD remains poorly investigated.

Method: Seventy BoNT-A–naïve patients affected by CD with predominant torticollis (40 patients) or head tremor (30 patients), and 30 age- and sex-matched healthy subjects (HS) were enrolled. Participants underwent myotonometric evaluation of both splenius capitis (SPL) muscles. This technique allowed the extraction of several biomechanical parameters of muscle tone, including frequency (F), stiffness (S), decrement (D), stress relaxation time (R), and creepability (C). In patients, experimental sessions were performed at baseline and approximately one month after BoNT-A treatment. Patients were also clinically assessed using the TWSTRS.

Results: We found that F, S, and D recorded at the level SPL on the affected side were significantly higher than those measured in the contralateral muscle and in healthy controls (p<0.01). In contrast, R and C were significantly reduced in the affected muscle compared with both the contralateral SPL in patients with CD and HS (p<0.05). BoNT-A treatment resulted in a significant reduction of F, S, and D values, along with an increase in R (p<0.05); however, these parameters did not fully return to levels comparable to those observed in HS. Notably, the reduction in F and S following BoNT-A treatment showed a positive correlation with the improvement in clinical severity as measured by the TWSTRS.

Conclusion: CD is characterized by objective alterations in specific biomechanical measures. These alterations are influenced by BoNT-A treatment. Our results support the use of an instrumental and objective approach to assess muscle tone abnormalities in CD.

References: 1. Patel S, Martino D. Cervical dystonia: from pathophysiology to pharmacotherapy. Behav Neurol. 2013;26(4):275-282. doi:10.3233/BEN-2012-120270
2. Jost WH, Hefter H, Stenner A, Reichel G. Rating scales for cervical dystonia: a critical evaluation of tools for outcome assessment of botulinum toxin therapy. J Neural Transm (Vienna). 2013;120(3):487-496. doi:10.1007/s00702-012-0887-7

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cervical-dystonia-the-objective-evaluation-of-muscle-tone/