A Pilot Study of Diagnostic Neuromuscular Ultrasound in Bell's Palsy

BACKGROUND AND PURPOSE Neuromuscular ultrasound of the cranial nerves is an emerging field which may help in the assessment of cranial neuropathies. The aim of this study was to evaluate the role of neuromuscular ultrasound in Bell's palsy. A second objective was to assess the possibility of any associated vagus nerve abnormality. METHODS Twenty healthy controls and 12 Bell's palsy patients were recruited. The bilateral facial nerves, vagus nerves, and frontalis muscles were scanned using an 18 MHz linear array transducer. Facial nerve diameter, vagus nerve cross-sectional area, and frontalis thickness were measured. RESULTS Mean facial nerve diameter was .8 ± .2 mm in controls and 1.1 ± .3 mm in patients group. The facial nerve diameter was significantly larger in patients than controls (P = .006, 95% CI for the difference between groups of .12-.48), with a significant side-to-side difference in patients as well (P = .004, 95% CI for side-to-side difference of .08-.52). ROC curve analysis of the absolute facial nerve diameter revealed a sensitivity of 75% and a specificity of 70%. No significant differences in vagus nerve cross-sectional area or frontalis thickness were detected between patients and controls. CONCLUSIONS Ultrasound can detect facial nerve enlargement in Bell's palsy and may have a role in assessment, or follow-up, of Bell's palsy and other facial nerve disorders. The low sensitivity of the current technique precludes its routine use for diagnosis, however, this study demonstrates its validity and potential for future research.