A potential upper motor neuron measure of bulbar involvement in amyotrophic lateral sclerosis using jaw muscle coherence

Abstract

Objective

To identify a novel, quantitative bulbar measure in amyotrophic lateral sclerosis (ALS) based on jaw muscle coherence. Methods: The myoelectric activities of masseter, anterior temporalis, and anterior belly of digastric were recorded bilaterally during a speech task in 12 individuals with ALS and 10 neurologically healthy controls, using surface electromyography. Coherence and directed coherence were calculated for all muscle pairs. The muscle pairs showing significant coherence and directed coherence in the beta-band (15–35 Hz) were identified and their mean beta-band coherence were (1) correlated with the kinematic (i.e. jaw acceleration time) and functional speech (i.e. speaking rate) measures that have been previously identified to be affected by bulbar ALS, across all participants, and (2) evaluated in terms of their efficacy in differentiating individuals with ALS from healthy controls. Results: Beta-band coherence was in general reduced in ALS relative to healthy controls, with the antagonistic and homologous muscle pairs being more affected than the agonistic pairs. Among all muscle pairs, the coherence between masseter and digastric (1) showed the strongest correlations with jaw acceleration time and speaking rate, and (2) differentiated individuals with ALS from healthy controls with the highest sensitivity (i.e. 0.92) and specificity (i.e. 0.90). Conclusions: Reduced beta-band coherence between masseter and digastric in ALS reflects weakened neural linkage between these muscles resulting from the disrupted cortical drive to the bulbar musculature. These findings provide preliminary evidence for jaw muscle coherence as a novel, quantitative measure of corticobulbar involvement, designed to improve bulbar assessment in ALS.

Keywords:

• Intermuscular coherence
• corticobulbar involvement
• quantitative measurement
• electromyography

Acknowledgements

The authors are grateful to the patients and families for their participation. The authors also thank Michaela Leahy for her assistance with data analysis.

Disclosure statement

The authors report no conflict of interest.

Additional information

Funding

This work was supported by the University of Kansas under the New Faculty General Research Fund.