Managing iatrogenic trigeminal nerve injury: a case series and review of the literature

Abstract

This study describes the management of 216 patients with post-traumatic iatrogenic lingual nerve injuries (LNIs; n = 93) and inferior alveolar nerve injuries (IANI; n = 123). At initial consultation, 6% IANI and 2% LNI patients had undergone significant resolution requiring no further reviews. Reassurance and counselling was adequate management for 51% IANI and 55% LNI patients. Systemic or topical medication was offered as pain relief to 5% of patients. Additional cognitive behaviour therapy (CBT) was offered to 8% of patients. Topical 5% lidocaine patches reduced pain and allodynia in 7% of IANI patients, most often used without any other form of management. A small percentage of IANI patients (4%) received a combination of therapies involving CBT, surgery, medication and 5% lidocaine patches. Exploratory surgery improved symptoms and reduced neuropathic area in 18 LNI and 15 IANI patients resulting in improved quality of life. In conclusion, the authors suggest a more diverse and perhaps holistic strategy for management of patients with iatrogenic trigeminal nerve injuries and recommend pragmatic assessment criteria for measurement of treatment success in these patients.

The most problematic outcome of dental surgical procedures with major medico-legal implications is injury to the trigeminal nerve. The prevalence of temporarily impaired lingual and inferior alveolar nerve function is thought to range between 0.5 and 2% for third molar surgery, whereas permanent injury caused by injection of local analgesics is much less frequent at 0.0001–0.01%. Trigeminal nerve injury is complex because it is the largest peripheral sensory nerve in the human body, represented by over 40% of the sensory cortex. The trigeminal nerve or ‘three twins’ supplies the face, eyes, mouth and scalp with general sensation in three divisions (ophthalmic, maxillary and mandibular), and innervates the mastication muscles.

The most commonly injured trigeminal nerve branches, the inferior alveolar nerve (IAN) and lingual nerve (LN) are different entities. The LN sits loosely in soft tissue compared with the IAN that resides in a bony canal. Injury to the third division of the trigeminal may occur due to a variety of different treatment modalities, such as major maxillofacial and minor oral surgery. Peripheral sensory nerve injuries are more likely to be persistent when the injury is severe, if the patient is older, there is increased duration between the injury and the review of the patient, and when the injury is more proximal to the cell body.

Subsequent to iatrogenic trigeminal nerve injury, the patient will experience reduced quality of life, psychological discomfort, social disabilities and handicap. Patients often find it hard to cope with such negative outcomes of dental surgery since the procedure is often elective and the patient expects significant functional or aesthetic improvements. Altered sensation and pain in the orofacial region may interfere with speaking, eating, kissing, shaving, applying make up, tooth brushing and drinking; in fact just about every social interaction.

Current management of these nerve injuries is inadequate. The focus misguidedly remains on surgical correction or laser therapy of the nerve itself with little or no attention to the patient’s complaints. A more holistic approach, such as medical or counselling intervention with consideration for the patients’ psychological, functional or pain related complaints is required. The fault partly rests with how these patients are assessed. Assessment tends to show little regard for the functional or pain evaluation with the main focus remaining on basic mechanosensory evaluation, which is not necessarily reflective of the patients’ difficulties. Oral surgery specialists assessing these injuries should follow guidelines from the World Health Organisation, which suggests that nerve injury outcomes should be assessed in terms of impairment, activity limitations, and participation restrictions. Guidelines set out by the International Association for the Study of Pain and European Federation of Neurological Societies should also be heeded. These recommendations involve assessment using quantitative thermosensory testing, pain profiling and quality of life questionnaires containing psychometric scales reflecting the important criteria by which the affectivity of interventions should be assessed. These recommendations, without exception, are holistic when compared with current reports evaluating the management of trigeminal nerve injuries.

Traumatic injuries to peripheral nerves pose complex challenges, and treatment of nerve injuries must consider all aspects of the inherent disability. A priority in managing these patients is reassurance and an honest opinion as to whether the nerve injury is permanent. This approach will give the patient a realistic platform from which to decide on future treatment and pain control and rehabilitation should be instituted as early as possible. Reparative surgery may be indicated when the patient complains of persistent problems related to the nerve injury, and is important for optimal physiological and functional recovery, but there remains a significant deficiency in evidence base to support this practice.

Patients’ presenting complaints may include functional problems due to the reduced sensation, intolerable changed sensation or pain that is predominantly intransigent to surgery. Frequently, poorly expressed psychological problems relating to the iatrogenesis of the injury and chronic pain are overlooked. Generally for lesions of the peripheral sensory nerves in humans, the gold standard is to repair the nerve as soon as possible after injury. The relatively few series of trigeminal nerve repair in humans relate mainly to repairs undertaken at significantly more than 6 months after injury, which is unsatisfactory. This phenomenon is peculiar to dentistry and may be based on the misconception that the majority of trigeminal nerve injuries resolve, when in fact, it is only lingual nerve injuries related to lingual access surgery that resolve in 10 weeks in 88% of cases.

It is evident from the literature review that there needs to be a cultural change in the choice of intervention, timing and outcome criteria when evaluating interventions for trigeminal nerve injuries. To date, there have been a very limited number of prospective randomized studies to evaluate the effect of treatment delay, and the surgical, medical or counselling outcomes for trigeminal nerve injuries in humans. This is probably due to the ethical difficulties of initiating such a study.

The aims of this study were to establish the main complaints of patients with iatrogenic trigeminal nerve injuries and determine how they are managed, with the aim of recommending improved criteria for assessing the outcomes of these interventions.

Materials and methods

Two hundred and fifty-four patients with trigeminal nerve injuries collected over 3 years were consulted at the authors’ institution. Thirty-eight patients presented with trigeminal neuropathy caused by neurological disease, malignancy, multiple sclerosis, sickle cell disease, known alcoholism, injury caused by non dental trauma, orthognathic surgery, diabetes, HIV, post-herpetic neuralgia, stroke or chemotherapy. The aetiology and functional status of the remaining 216 injuries were evaluated and their management documented.

All patients were seen and assessed by a single clinician (TR) who obtained a detailed history. This included the date and mode of injury and the patients’ self-assessment of neurosensory function in terms of reduced function (hypoaesthesia, anaesthesia), and neurogenic discomfort (paraesthesia, dysaesthesia, allodynia, dysgeusia, ageusia). The related interference with daily function was explored on a task basis, and psychological effects were specifically identified, the details of which are described elsewhere.

A series of standardized tests of neurosensory functions was undertaken on all patients by the same observer (TR) based on recommendations by Robinson et al. Key factors assessed were size and extent of the neuropathic area, subjective function, mechanosensory function, functional problems and pain profiling.

The percentage neuropathic area (percentage of extra-oral and intra-oral dermatomes) was mapped by running closed forceps gently over the surface from the unaffected area to the injured zone, mapping points when the patient acknowledged a change in sensation. A neuropathic area of 100% within the extra-oral dermatome indicated that the whole mandibular nerve extra-oral skin area of the injured side was affected. A neuropathic area of 100% within the intra-oral mucosa indicated that the whole intra-oral mucosa area of the injured side was affected. Pain scores were rated on a visual analogue scale, where 0 indicated no pain and 10 the worst pain imaginable. Mechanical allodynia was indicated by evoked pain in response to touch.

Following assessment, the patient was informed of the diagnosis, the degree of injury, the likely cause and permanency of the injury, followed by a discussion of the possible strategies to manage their symptoms and their expectations. The consultations usually lasted 30–40 min. Patients were seen on more than one occasion and were informed at each consultation of how their symptoms may relate to current understanding of neuroscience with explanations of neuropathic pain (for example cold allodynia). The patients were always offered the contact details of the clinician.

The strategy for selecting the mode and timing of intervention was based on the cause of the injury, the patient’s symptoms, the extent and permanency of the injury and the patient’s choice. The key management strategies included counselling and reassurance, medication and surgery (exploration with or without decompression or direct anastomosis). As time progressed, the service developed by providing liaison psychiatric and psychological support in the form of cognitive behavioural therapy (CBT). CBT was provided by initial screening by a consultant liaison psychiatrist and provided by a clinical psychologist and was based on both qualitative analysis and results from specific psychometric questionnaires, of which one was the PainDETECT questionnaire. Other novel strategies included topical 5% lidocaine patches, topical clonazepam and botulinum toxin type A (Botox) injections. More traditional pain management strategies included systemic pregabalin, oxcarbazepine, venlafaxine and nortriptyline for chronic pain. Outcomes assessed were pain relief, improved functionality and ability of the patient to cope with their iatrogenic post-traumatic neuropathy.

Data analysis

All data was analysed using SPSS and Excel. Student’s t -tests were carried out for the analysis of the mean, where P values less than 0.05 were statistically significant.

Data analysis

All data was analysed using SPSS and Excel. Student’s t -tests were carried out for the analysis of the mean, where P values less than 0.05 were statistically significant.

Results

Two hundred and sixteen patients, referred from many parts of the UK, were involved in this study. One hundred and twenty-three patients had IAN injury (IANI, 57%) and 93 patients had LN injury (LNI, 43%). In this cohort, the authors present a more holistic assessment of patients with post-traumatic neuropathy with equal focus on mechanosensory results and the patients’ experience of pain and altered sensations, and functional morbidity.

LNI patients presented with a mean age of 38.4 years (range 20–64 years) and IANI patients with a mean age of 44.0 years (range 22–85 years). The majority of these injuries were caused by third molar surgery carried out under local anaesthesia ( Fig. 1 ). Time from injury to examination followed a skewed distribution with median of 6 months (arithmetic mean of 16.7 months; standard deviation (SD) 41.5 months; range 1 week to 360 months) for IANI patients, and a median of 5.5 months (arithmetic mean of 17.3 months; SD 43.3 months; range 1 week to 312 months) for LNI patients.

Fig. 1
Key causes of IANI and LNI. The majority were caused by third molar surgery, followed by local anaesthetic. Only IANI were caused by implants and endodontics.

Nerve injuries were defined as permanent if caused by implant or endodontic procedure (>1 month), third molar surgery and other causes (>6 months). The majority of IANI (64%) and LNI (69%) patients had permanent injury, in comparison with only 7% and 14% with temporary IANI and LNI, respectively. Twenty-nine percent IANI patients and 17% LNI patients were under repeated review as their lesions continued to resolve with minimal pain or functional problems not requiring any specific intervention with the exception of the initial and subsequent consultations.

Approximately 70% of all patients presented with neuropathic pain, despite the additional presence of anaesthesia and hypoaesthesia, and other neuropathic symptoms, such as paraesthesia ( Fig. 2 ). Neuropathy was demonstrable in all patients with varying degrees of loss of mechanosensory function, paraesthesia (74%), dysaesthesia in the form of burning pain (18%), mechanical allodynia (by pain to light touch discrimination; 32%) and mechanical hyperalgesia (by pain to sharp-blunt discrimination; 46%). Although IANI patients suffered from a larger mean intra-oral and extra-oral neuropathic area (58% and 56%), their mean subjective function value of 8.0 was slightly better than the 5.0 of the LNI patients. Key functional problems experienced by this cohort are shown in Fig. 3 .

Fig. 2
Incidence of pain, anaesthesia and hypoaesthesia, and neuropathic symptoms (e.g. pins and needles, paraesthesia) in all patients. Although anaesthesia, pain and other neuropathic symptoms such as paraesthesia are different sensations, patients experienced a mixture of symptoms in different parts of the neuropathic area. For example, pain may occur in the chin area of a patient with IANI despite numbness of the lip. Thirty-two patients experienced anaesthesia, pain and other neuropathic symptoms in the form of paraesthesia.

Fig. 3
Interference of symptoms with functionality of the patients. The majority of IANI and LNI patients had problems with speech and eating; speech significantly affected more LNI patients (** P < 0.001). Significantly more IANI patients had difficulties with brushing their teeth (** P < 0.001), drinking (*** P < 0.0001) and sleep (* P < 0.05). Kissing was affected in equal percentages of IANI and LNI patients.

All patients with permanent nerve injury were reassured that their injury will not worsen, while at the same time it will not improve, and that it will not predispose them to developing any pathology in the area. They were also offered an explanation of the physiology of nerve injuries and were told how difficult they are to treat. This was the only form of management for 63 IANI (51%) and 51 LNI (55%) patients, as there was no indication for medical, surgical or liaison psychiatric assistance in the form of CBT ( Fig. 4 ). Seven IANI patients and two LNI patients who were only reassured, because medical, surgical or CBT treatment was not indicated, had recovered well from their injuries and were discharged from hospital. CBT alone was offered to 5% of all patients (seven IANI and four LNI patients), while 5% of IANI patients had CBT combined with another treatment method ( Table 1 ). It is anticipated that these values will increase over time, as CBT sessions provided by a clinical psychologist had only just started to be offered in the authors’ multi-disciplinary facial pain clinics.

Fig. 4
Key management modes for patients with IANI and LNI.

Table 1
Key methods used for managing patients with IANI and LNI.
Number (%) of patients
Management method IANI LNI
Reassurance and counselling 63 (51.2) 51 (54.8)
Reassurance and counselling; patient discharged 7 (5.7) 2 (2.2)
CBT:
– Alone 7 (5.7) 4 (4.3)
– With surgery 2 (1.6)
– With medication 1 (0.8)
– With topical 5% lidocaine patches 1 (0.8)
– With surgery and topical 5% lidocaine patches 1 (0.8)
– With medication and topical 5% lidocaine patches 1 (0.8)
Surgery:
– Carried out alone 15 (12.2) 18 (19.3)
– Informed patient but refused surgery 6 (4.9) 12 (12.9)
Medication:
– Alone 4 (3.3) 2 (2.2)
– Refused by patient, no surgery or CBT 1 (0.8) 1 (1.1)
– Medication and CBT refused by patient 2 (1.6)
– Medication finished 3 months prior to appointment 1 (1.1)
– Pregabalin and topical lidocaine intra-orally 1 (1.1)
Topical 5% lidocaine patches:
– Alone 8 (6.5)
– Alone with positive results; discharged from clinic 2 (1.6)
– Alone but gave adverse reaction so patients given medication 2 (1.6)
– With surgery 2 (1.6)
– With medication 1 (0.8)
Alternative:
– Chew chillies 1 (1.1)
– Speech therapy 1 (1.1)
– Pregabalin and tabasco sauce 1 (1.1)
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Managing iatrogenic trigeminal nerve injury: a case series and review of the literature
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