Innovative Measures of Speech and Swallowing Dysfunction in Neurological Disorders
Speech and swallowing abnormalities are important symptoms associated with disorders of the central nervous system, motor neuron disease (such as amyotrophic lateral sclerosis), myasthenia gravis, and primary muscle conditions. In addition to characterizing the evolution in muscle architecture that could underlie associated orofacial weakness, identifying new ways to measure these abnormalities is critical to the development and testing of novel treatment approaches. As painless, non-invasive, portable technologies, quantitative ultrasonography (QUS) and electrical impedance myography (EIM) could meet the need for objective measures of speech and swallowing dysfunction.
In QUS, acoustic energy is applied to a muscle of interest; the resultant pictorial data are translated into a single value that reflects the health of the imaged muscle. Similarly, in EIM, a high-frequency, low-intensity alternating electrical current is applied to individual muscles, and the resulting voltages measured. Impedance values reflect changes in muscle architecture, including fiber atrophy, inflammation, and the replacement of muscle with fat or connective tissue. Both of these user-friendly methods can provide sensitive indicators of neuromuscular disease status when applied to the limbs. Although they have also been used to evaluate orofacial muscles in healthy volunteers and patients with primary muscle disorders, they have not yet been systematically studied in patients with a range of neurological conditions.
When applied to muscles of the face and tongue, such tools could 1. Improve accuracy of early diagnosis; 2. Allow monitoring of speech and swallowing dysfunction over time; 3. Help individualize care; and 4. Serve as biomarkers in clinical trials. We propose that QUS and EIM will provide convenient, reliable, clinically meaningful surrogate markers of orofacial dysfunction in a variety of neurologic conditions.