Abstract
This report highlights the management of a rare complication, namely allodynia, which arose following mandibular advancement surgery. A 56-year-old female underwent bilateral sagittal ramus advancement osteotomy. Postoperatively, she developed allodynia corresponding to the distribution of the left inferior alveolar nerve. A hierarchical pathway of topical and pharmacological agents followed by ablative techniques was used without success. Eventually, electrical neuromodulation via a motor cortex stimulator was implemented to manage the symptoms. The report serves to outline treatment options available and the risks associated with this treatment.
Chronic neuropathic pain associated with the distribution of the inferior alveolar nerve (IAN) is a rare complication that can occur following orthognathic surgery involving the mandible. The incidence of this condition following mandibular osteotomy is unknown, but some studies have reported that in patients with known sensory nerve injury, 5% may develop neuropathic pain following the procedure.
The goal of treatment for chronic pain is to make pain tolerable and to improve functionality and quality of life for the patient. Conventional medical management may include pharmacological interventions such as non-steroidal anti-inflammatory drugs, tricyclic antidepressants, anticonvulsants, analgesics and opioids. Non-pharmacological interventions, include physiotherapy, acupuncture, transcutaneous electrical nerve stimulation and psychological therapies. If conventional management is unsuccessful, it may be possible to treat the cause of the pain directly through more invasive measures such as spinal cord stimulation (SCS), motor cortex stimulation (MCS) and even deep brain stimulation (DBS).
The aim of this case report is to describe a patient who underwent a mandibular advancement osteotomy and developed chronic neuropathic pain in association with allodynia postoperatively. The pain pathway resulted in the condition being managed through MCS. To the authors’ knowledge this is the first published report on the management of chronic neuropathic pain following mandibular osteotomy using this technique and presents clinicians with the hierarchical treatment options available to manage this debilitating complication.
Case report
A 56-year-old female was referred by her general dental practitioner to the Orthodontic Department at the University Dental Hospital, Cardiff because her upper teeth protruded and she had difficulty chewing food. Clinically the presentation was a Class II division 1 incisor relationship on a Skeletal 2 dental base related to mandibular deficiency. The malocclusion was complicated by an increased overjet, an increased, traumatic overbite and multiple missing posterior units. A lateral cephalometric radiograph confirmed the clinical picture of mandibular deficiency.
Owing to the skeletal aetiology of the malocclusion, treatment options based around upper and lower fixed appliances for orthodontic decompensation followed by mandibular advancement surgery were discussed with the patient. The risks and complications of the surgery, including neurosensory deficit, were discussed and the patient formally consented prior to the surgery.
Following a limited course of orthodontic treatment, mandibular advancement surgery was carried out with favourable splits of the proximal and distal segments and an intact IAN bilaterally documented throughout the procedure. Although the orthodontic appliances were removed 6 months after the surgery, a neuropathic pain corresponding to the left IAN radiating to the lower lip, teeth and gingivae developed 1 month postoperatively. The pain was continuous and burning with additional paroxysmal stabbing pains and marked allodynia throughout the affected area, which was evoked by light touch or by hair or feather. Visual analogue scales (VAS) reported her intensity to vary between 9/10 and 10/10. A pharmacological approach to pain management was initially adopted. Medications including gabapentin (1800 mg daily), prothiaden (75 mg daily) and amitriptyline (125 mg daily) were prescribed. These were primarily in response to whether an improvement in her symptoms was seen and/or whether any adverse side-effects were evoked. Ultimately the medications did not control her symptoms to any degree of manageability and during acute episodes of pain, nerve ablation direct to the mental nerve was used. This included local anaesthetic blocks (0.5% bupivacaine), cryotherapy and pulsed radiofrequency ablation. Despite this, little improvement was seen.
A referral was made to a neurosurgeon, who noted that the failure of local nerve blocks suggested a degree of central sensitization and therefore the option of electrical neuromodulation was discussed. Owing to the patient’s reduced quality of life and the exhaustion of conservative treatment options she consented to the insertion of an SCS. The SCS incorporated a paddle electrode system which was inserted at C2 and C3 to the left of midline near the trigeminal spinal nucleus caudalis ( Fig. 1 ). This was connected to a rechargeable pulse generator located beneath the right axilla. The stimulation frequency was set at 120 Hz with a pulse width of 250 ms and amplitude of 6 V.
Although the recovery was uneventful, it was not possible to achieve stimulation of the trigeminal territory. Instead stimulation was felt throughout the left upper limb and the left occipital scalp. Even with the amplitude high enough to induce a motor response in the limb, the patient felt nothing in the face.
Therefore, after 4 months, the SCS was substituted for a right sided MCS. The procedure was performed via craniotomy with the electrodes of the MCS placed in the region of the central sulcus and motor cortex using image navigation ( Fig. 2 ). Once the electrode paddle of the MCS was secured subdurally, the original pulse generator used for the SCS was disconnected and re-connected to the MCS. Confirmation of the position of the lead on the motor cortex was performed with a cortical stimulator, which failed to elicit a motor response. However, when the MCS was stimulated through the implanted system using a block of four contacts as cathodes at a frequency of 2 Hz and pulse width 350 ms, contractions first in the trapezius muscle and then face at 16 mA (4 mA at each contact) were seen. Various stimulation parameters were used postoperatively with the final configuration set at a frequency of 30 Hz, pulse width 730 ms and motor threshold of 12 mA. This was set on a cycling of 90 min on and 90 min off. The SCS was left deactivated in situ to minimize further morbidity to the patient.
Following insertion of the MCS, the patient reported a 50–60% improvement in baseline VAS pain ratings. There were no significant side effects and she was able to be examined without undue distress implying an alleviation of allodynia. Although the effect of the MCS varied from time to time she was able to control her symptoms and experience a much improved quality of life.
Discussion
Management pathways for chronic neuropathic pain are typically hierarchal in nature. Table 1 summarizes the main options available to clinicians. As a guideline, electrical neuromodulation can be recommended as a treatment option for adults who continue to experience chronic neuropathic pain (measuring at least 50 mm on a 0–100 mm VAS) for at least 6 months despite the use of conventional medical management. SCS, MCS or DBS can be considered.
| Treatment group | Specific treatment |
|---|---|
| Topical | Local anaesthetic |
| Capsaicin | |
| Local | Transcutaneous electrical stimulation |
| Acupuncture | |
| Thermal (hot, cold) | |
| Vibration | |
| Massage | |
| Nerve blocks | Somatic nerve, plexus or root |
| Sympathetic ganglia | |
| Regional guanethidine | |
| Central stimulation | Spinal cord stimulation |
| Motor cortex stimulation | |
| Deep brain stimulation | |
| Spinal drugs | Epidural |
| Intrathecal | |
| Pharmacological | Non-steroidal anti-inflammatory drugs Opioids Tri-cyclic antidepressants Anticonvulsants |
| Surgery | Decompression |
| Psychological | Behavioural measures |
| Pain management programmes | |
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