Latrogenic damage to the lingual nerve: reliability of neurophysiological tests for the diagnosis and the outcome assessment of reparative microsurgery

Objectives: Lingual nerve damage can occur during oral surgery, especially in case of avulsione of the lower VIII teeth. This study was conducted to verify the validity and reliabilitay of neurophysiological evaluation of lingual nerve iatrogenic damage for the preoperative diagnosis and follow-up. Materials: 10 patients with documented iatrogenic lesion of the lingual nerve (anesthesia or severe hypoesthesia and ageusia or severe hypogeusia of half of the tongue) were evaluated by examination of masseteric inibitory reflex (MIR) both before microsurgical reconstruction with neurrorhaphy and in a post-operatory follow-up. Methods: We evaluated the tactile and pain sensory threshold (expressed in milliamps) on the unaffected side of the tongue by means of electrical stimulation delivered with teflon-coated needle electrodes placed on the upper surface of the tongue at an interelectrodes distance of 1 cm. MIR was elicited at 6 or 9 times pain threshold stimulus strength. The same test was conducted on the affected side with comparison of threshold values (percentage ratio) and evaluation of MIR at different intensities of stimulation (intensity of the healthy side and then 9 to 9 times the intensity of the tactile and pain threshold if found). The study was conducted before the microsurgery and subsequently at 6 and 12 months after surgery. Results: The tactile and pain sensory threshold was significantly increased on the affected side before surgical reconstruction (unaffected side: tactile threshold 1.90+/-1.5 mA, pain threshold: 6.4+/-5.2 mA; ratio affected/unaffected side threshold: tactile 10-60%,pain 8-52%). The SP1 and SP2 of the MIR were altered (absence of the components or poor representation of them). In the 12 months follow-up all patients showed a recovery of sensory modalities, with improved tactile and pain sensitivity reflected in an average value ratio of 49.0% and 47.% (in two patients recovery was respectively 70% and 80%) and return of MIR responses, although with elongated latencies. Discussion: The method applied has proved useful in order to objectify a lingual nerve injury before microsurgical repair. Furthermore, it has been helpful in verifying the recovery of the sensitivity in the subsequent follow-ip. Conclusion: Microsurgical repair of lingual nerve lesions can dramatically improve the symptoms of patients and the collaboration between maxillofacial surgeon and neurophysiologist is definitely useful for this aim.