Subjective sensory symptoms associated with axonal and demyelinating nerve injuries after mandibular sagittal split osteotomy.

PURPOSE: The effect of the type of nerve injury on subjective sensory disturbances and recovery has not been addressed in orthognathic surgery. Using neurophysiologic monitoring during 19 bilateral sagittal split osteotomy operations, we were able to classify intraoperative inferior alveolar nerve injuries as either axonal or demyelinating. This study aimed to analyze the quality and extent of the subjective sensations experienced by the patients after these 2 injury types at different time points up to 12 months. MATERIALS AND METHODS: Of the 36 injured nerves, 21 showed signs of demyelinating injury and 15 showed signs of axonal damage. The quality of subjective sensory symptoms was asked about at 2 weeks and 1, 3, 6, and 12 months postoperatively and classified into 4 categories: normal, negative, positive (including pain), and mixed sensations. In addition, the extent of the sensory alteration was determined by measuring the affected skin regions from symptom charts. RESULTS: The quantity, quality, and evolution of experienced subjective sensations differed between the injury types during follow-up: Subjective sensations normalized more rapidly after demyelinating-type injuries than after axonal-type injuries. Persistence of mixed sensation patterns at 3 months and appearance instead of disappearance of positive sensory phenomena after 3 months indicated axonal damage. Painful sensations at 1 month or later after surgery indicated axonal damage and predicted poor recovery and more long-term sequelae. CONCLUSIONS: Postoperative pain at 1 month and type of nerve injury are important prognostic factors for the persistence of subjective symptoms and development of neuropathic pain.

Neurophysiology and genetics of burning mouth syndrome.

BACKGROUND AND AIMS: Neuropathic mechanisms are involved in burning mouth syndrome (BMS), and variation of the dopamine D2 receptor (DRD2) gene contributes to experimental pain perception. We investigated whether neurophysiologic findings differ in BMS patients compared to healthy controls, and whether 957C>T polymorphism of the DRD2 gene influences thermal sensitivity or pain experience in BMS. METHODS: Forty-five BMS patients (43 women), mean age 62.5 years, and 32 healthy controls (30 women), mean age 64.8 years, participated. Patients estimated pain intensity, interference, suffering and sleep with Numeric Rating Scale. Blink reflex tests of the supraorbital (SON), mental (MN) and lingual (LN) nerves, and thermal quantitative sensory testing were done. The results were analysed with ANOVA. DRD2 gene 957C>T polymorphism was determined in 31 patients, and its effects on neurophysiologic and clinical variables were analysed. RESULTS: Cool (p = 0.0090) and warm detection thresholds (p = 0.0229) of the tongue were higher in BMS patients than controls. The stimulation threshold for SON BR was higher in patients than in controls (p = 0.0056). The latencies of R2 component were longer in BMS patients than in controls (p = 0.0005) at the SON distribution. Habituation of SON BR did not differ between the groups. The heat pain thresholds were highest (p = 0.0312) in homozygous patients with 957TT, who also reported most interference (p = 0.0352) and greatest suffering (p = 0.0341). Genotype 957CC associated with sleep disturbances (p = 0.0254). CONCLUSIONS: Burning mouth syndrome patients showed thermal hypoesthesia within LN distribution compatible with small fibre neuropathy. The DRD2 957C>T genotype influences perception and experience of BMS pain. SIGNIFICANCE: The results confirm earlier findings of neuropathic pain in BMS. The DRD2 957 C>T genotype influences perception and experience of clinical pain in BMS.