Clinical Applicability of Ultrasound Shear Wave Elastography in Patients under Hypoglossal Nerve Stimulation Therapy

Relationship between stiffness of genioglossi (GG) and geniohyoidei (GH) muscles under electric hypoglossal nerve stimulation therapy (HNS) in relation to success of therapy was investigated with additional special focus on tongue movement. Patients and Methods: Clinical and sleep laboratory parameters of a cohort of 18 patients with known shear wave velocity (SWV) data of the ipsilateral and contralateral musculi GG and GH (sGG, sGH and nGG, nGH) before and under HNS therapy were analyzed. The SWV was already determined using the ultrasonic shear wave elastography (US-SWE) technique. Results: Median Epworth Sleepiness Scale (ESS) was 8 (IQR 12), median baseline Apnoe-Hypopnoe Index (AHI) 31.65 (IQR 25.1), median AHI under HNS therapy 16.3 (IQR 20.03). Therapy success: 9/18 patients (AHI during therapy < 15/h). There was no significant difference in SWV (sGG, sGH, nGG and nGH) between therapy responders and non-responders during therapy. Also, no difference could be seen with respect to the difference and increase in SWV values without and with stimulation. Examination of SWV values (sGG, sGH, nGG, nGH during stimulation, difference of SWV values stimulation - no stimulation, increase factor of SWV) revealed a significant negative correlation between the AHI under therapy and the measured SWV of the musculus GH of the contralateral side during stimulation (-0.622, p = 0.006). Patients with bilateral protrusion of the tongue differed regarding to therapy success in increase in SWV in sGG (p = 0.032). Tongue protrusion to contralateral: A significant difference between patients with AHI during therapy < 15/h in SWV values at sGG without stimulation (p = 0.021) was seen, with also a correlation to the current AHI under therapy (p = 0.047) and the change factor of the AHI (p = 0.015). Conclusion: Stiffness of the target muscle does not appear to be an isolated measure of the success of HNS therapy. This observation may have implications for future decision-making processes in the process of titrating electrical therapy parameters. But the technique of US-SWE may be useful for future research of the neurophysiology of the tongue and OSA phenotyping.