Quantifying orofacial muscle stiffness using damped oscillation

Muscle stiffness can reflect muscle tone, often presumed to be aberrant in persons with dysarthria. This exploratory study used the Myoton-3 to assess stiffness of the lateral tongue and mid-cheek in 10 participants with various neurologic disorders - primarily lower motor neuron (n = 6), primarily upper motor neuron (n = 4), and neurologically normal adults (n = 4). The Myoton delivered a 25-ms pulse perturbation to the surface of the structure of interest and sensed the response with an internal accelerometer. The resulting acceleration curve was used to determine frequency of oscillation and decre-ment of damping; stiffness was derived from the linear displacement of tissue per force of the perturbation. Tongue stiffness was significantly lower for the LMN group than for the normal control group, consistent with the assumption that hypotonia accompanies flaccidity. Tongue stiffness did not differ for the UMN group, nor did cheek stiffness, oscillation frequency or decrement differ between any groups. These preliminary findings indicate that stiffness can be determined from the surface of the tongue and cheek, and may be indicative of low muscle tone in LMN lesions. Although methodologic challenges remain, this novel approach has the potential to quantify orofacial muscle stiffness and document potential changes in muscle tone with disease and treatment.