Trigeminal Neuralgia for General Practitioners
A short report of trigeminal neuralgia for general practitioners.
Trigeminal neuralgia (TN) is a severe type of chronic neuropathic facial pain. Despite symptoms being described for centuries, a recent survey found the diagnosis of TN can easily be missed.  There are a number of reasons for this but, importantly, it is the role of the general practitioner (GP) that has not received due attention in the literature.
The aims of this article are to review the presenting clinical features of TN, the differential diagnosis, evidence-based treatment, referral options and potential barriers to good outcomes.
There are effective medical and surgical treatment guidelines for TN  and, given all patients have a right to pain management,  it is appropriate to review the current evidence-based management guidelines and identify the causes of suboptimal treatment outcome. Suggestions for improving care for patients suffering from TN will also be provided.
Could it be trigeminal neuralgia?
TN is a rare condition with an incidence of 4.3/100 000 people per year.  The pain is typically described as severe, brief, lancinating, triggerable, paroxysmal and usually unilateral. It occurs within the distribution of the trigeminal nerve most commonly within the third and second divisions (see figure 1). The pain arises spontaneously. It does not following previous trauma, shingles, stroke, cancer, or orofacial, ear, nose or throat surgeries.
In addition to its rarity, a wide differential diagnosis exists for pain within the head and face, including more common dental and temporomandibular joint disorders, as there is a complex neuroanatomical overlap between pain sensitive structures. It is important to make the diagnosis of TN because it is eminently treatable. However, TN is a clinical diagnosis based entirely on history, and taking a pain history can be difficult. This last point likely contributes to a delay in diagnosis.
Standardised questionnaires streamline the diagnosis of facial pain, particularly if the diagnosis of TN is suspected. The Burchiel facial pain classification and questionnaire [5, 6] is simple, web-based and has high sensitivity and specificity. It uses an artificial neural network to learn, and can be used by patients to assist their doctors. A distinction is made between type 1 (chiefly brief episodic pain) and type 2 (chiefly chronic constant pain) and other causes of trigeminal nerve injury causing trigeminal neuropathy, which has important prognostic and treatment implications.
Examination of the patient with TN during an attack of neuropathic pain is usually unmistakeable, consistent with its other name ‘tic douloureux’. Between attacks, the neurological exam is normal and the patient appears entirely well with stimulation of the orofacial area not triggering pain. An abnormal neurological exam particularly sensory loss, other cranial neuropathy, visual disturbance or long tract signs should prompt consideration of alternative diagnoses including multiple sclerosis, intracranial malignancy, post-stroke pain or post-herpetic neuralgia.
The aetiology of TN may be due to neurovascular compression of the trigeminal nerve or damage within that nerve; for example, multiple sclerosis. However, neither pathology may be evident in many cases suggesting aetiologies yet to be determined in future research. Nevertheless, magnetic resonance imaging (MRI) of the brain should be performed for all cases of TN to specifically rule out these causes. It can be ordered by GPs with the relevant clinical history of suspected TN, but should not delay treatment.  The imaging should be interpreted in context by a relevant specialist and is not, in itself, diagnostic.
Treatment starts in primary care
The first line treatment of TN is medical. Hospitalisation is rarely needed, but may be required if the pain cannot be managed or the patient cannot eat or drink.
Carbamazepine is the drug of choice and is effective with a number needed to treat (NNT – the number of patients treated for one patient to get a 50% reduction of pain) of 1.7 (1.3–2.2). [7, 8] Doses of 100–200 mg bd titrating upwards can be prescribed until the relief of pain, or to a maximum of 1200 mg a day and immediate and controlled release formulations are available. Side effects can be common including ataxia, cognitive impairment, drug interactions, induction of liver enzymes, hepatotoxicity, syndrome of inappropriate antidiuretic hormone and rarely life-threatening reactions such as agranulocytosis or Stevens–Johnsons syndrome.  Oxcarbazepine, related to carbamazepine, appears to have similar efficacy and may be better tolerated. (10)
Lamotrigine, gabapentin, pregabalin, baclofen, phenytoin and botulinum toxin type A have also been studied, and can be used alone or as additional therapy. Although they are less effective than carbamazepine or oxcarbazepine, they are frequently prescribed and may be better tolerated in some patients. There is no evidence that opioids are effective. Some patients may not respond to any agent, become tolerant to medication over time or the pain may become refractory to pharmacotherapy. 
Don’t go it alone – an early surgical opinion should be considered
The second line of treatment for TN is surgery, and usually it should be considered sooner rather than later. Reasons for this include the failure of pharmacotherapy to control pain; the risk of progression of acute to chronic pain, which may be more difficult to treat;  patient-reported preferences for surgery;  and improved pain relief with surgery, compared to medical therapy in one longitudinal cohort study. 
Although there is a lack of evidence, current guidelines recommend surgical referral when pain becomes refractory to pharmacological therapy, when pain is controlled but side effects are unacceptable, or pain is controlled but the patient wants to come off medication long term following successful surgical intervention.
There are many additional benefits to early referral to a specialist, who can both medically and surgically manage TN in a multidisciplinary team. These include clarification of the exact clinical diagnosis and suitable cross referral, medication optimisation, patient education, expedited medical imaging, and patient support and future management planning because for a significant number of patients, TN is a chronic relapsing condition.
What is the best surgical option for my patient?
The surgical options for TN can be divided neatly into microvascular decompression surgery (MVD) and lesional procedures to the trigeminal nerve. There are no randomised controlled trials comparing surgical options, with the best evidence arising from non-randomised comparison or single treatment outcome studies.  In day-to-day practice, decision-making often includes multiple variables such as pain aetiology, clinical pain phenotype and distribution, surgeon expertise, patient preference and surgical risk analysis.
MVD is the procedure of choice for a patient with TN and vascular compression, with the best chance of short- and long-term pain relief as surgery addresses the structural cause of pain and is non-destructive to the nerve. In the best hands, 70% of selected patients will be pain free at 10 years.  A craniotomy, however, is often perceived as daunting by the patient, as there are risks of neurological deficit along with a required inpatient stay and further recovery at home.
In patients without vascular compression, lesional procedures are the preferred choice. These include radiosurgery, which delivers highly focused radiotherapy to the trigeminal nerve, or percutaneous procedures to injure the trigeminal ganglion and nerve root. They can be performed under sedation or a brief general anaesthetic with X-ray or stereotactic guidance as a day procedure. The outcomes of these treatments have a high (80–90%) chance of initial pain relief, but with significant chance of pain recurrence over time; however, these procedures can be easily repeated.  Not everybody benefits from surgery and multidisciplinary care and support is important for all patients.
A woman, aged 57 years, was referred to the author by her current GP with a three-year history of left facial pain. The facial pain, which had come on spontaneously, was severe, triggerable and would limit speech and the ability to eat. The pain would go into remission and at other times was so severe that the patient attended emergency departments, was unable to work or felt suicidal.
She consulted numerous medical practitioners, a dentist and a neurosurgeon. The patient reported a number of her providers were unable to make the diagnosis and this was made by the patient. Carbamazepine and gabapentin had been trialled without benefit, but cognitive side effects and worsening pain limited efficacy. Neurological examination was normal, but the patient was obviously having attacks of facial pain during the consultation.
An MRI scan showed vascular compression of the left trigeminal nerve at the dorsal root entry zone, no mass lesion and no evidence of demyelination. The patient underwent a left MVD of the trigeminal nerve. At surgery there was clear neurovascular conflict between a branch of the superior cerebellar artery and the trigeminal nerve, and Teflon felt was interposed between the two.
Following surgery, the patient had immediate relief of her facial pain, was discharged on day three and has remained pain-free and off pain medication since.
In this true but, unfortunately, not unique case, a patient with medically refractory TN sought help from multiple medical providers, including specialists and emergency departments, and ultimately researched the diagnosis herself before definitive care was provided.
GPs can contribute to better outcomes for patients with TN with prompt recognition, evidence-based treatment of neuropathic pain, and rapid referral to effective medical and surgical treatments. We need to raise medical awareness in primary care about TN, use evidence-based guidelines and address barriers to treatment. TN should be treated with a focus on coordinated multidisciplinary input in dedicated clinics. Neurosurgical input should be considered early and could be facilitated with telehealth advances in the Australian setting. Future studies on the knowledge of GPs about TN may facilitate this.
- Trigeminal neuralgia most often first presents to the GP.
- The diagnosis of TN is based on a history of severe pain in the trigeminal nerve distribution.
- The neurological exam is normal.
- Carbamazepine is the most effective medication with NNT 1.7.
- GPs can improve patient outcomes by early recognition, appropriate medication and early referral.
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