Evaluation of lip sensory disturbance using somatosensory evoked magnetic fields

Objective: To evaluate lip sensory dysfunction in patients with inferior alveolar nerve injury by lip-stimulated somatosensory evoked fields (SEFs). Methods: SEFs were recorded following electrical lip stimulation in 6 patients with unilateral lip sensory disturbance and 10 healthy volunteers. Lip stimulation was applied non-invasively to each side of the lip with the same intensity using pin electrodes. Results: All healthy volunteers showed the earliest response clearly and consistently at around 25 ms (P25m) and at least one of the following components, P45m, P60m, or P80m, over the contralateral hemisphere. The ranges of the peak latencies were 23-33, 42-50, 56-67, and 72-98 ms for right-side stimulation and 23-34, 46-49, 52-68, and 71-90 ms for left-side stimulation. Affected-side stimulation did not evoke P25m component in any patients, but invoked traceable responses in 5 patients whose latencies were 57, 89, 65, 53, and 54 ms. Unaffected-side stimulation induced P25m in 2 patients at 27 and 25 ms, but not in the other 4 patients. Conclusion: The P25m component of lip SEFs can be an effective parameter to indicate lip sensory abnormality. Significance: Lip sensory dysfunction can be objectively evaluated using magnetoencephalography.