Trigeminal Neuralgia

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Diagnosis and reasoning

The patient who presents with facial pain should undergo a conscientious clinical assessment, as many of the underlying conditions can be diagnosed from the history and examination itself. Thus, careful evaluation of the pain in this 34 year old man shows the pain to be repetitive, abrupt, paroxysmal, and triggered by movements. These characteristics are typical of trigeminal neuralgia (TN); the presence of a trigger zone (i.e. the nasolabial groove) lends further credence to this diagnosis. However, it should be noted that conditions such as temporomandibular joint (TMJ) syndrome, migraine and cluster headaches, giant cell arteritis, post herpetic neuralgia, diseases of the ears and nose, chronic sinusitis, dental caries and atypical facial pain can also present in this manner. TMJ syndrome is perhaps the etiology that could most closely mimic this presentation; the intermittent nature and aggravation with movements favor this diagnosis, but in the absence of crepitus and limited range of movement of the joint (which are its cardinal features), it becomes less plausible. Episodes of migraines and cluster headaches last for longer durations, while the pain is usually described as throbbing, and sometimes excruciating; the periorbital and temporal areas are more often involved. These conditions are also largely associated with autonomic symptoms, which are deficient here. Giant cell arteritis is unusual in this age group, but should be a diagnostic priority in patients over 55 years. Diseases of the ears and nose occur in accordance with abnormalities in the specific system examination; these are normal in this patient. The absence of nasal discharge, postnasal drip and sinus tenderness make chronic sinusitis less of a possibility. Post herpetic neuralgia is also unconvincing in the absence of a history of herpes zoster. Dental caries are unlikely, given his good oral hygiene. However, these should still be kept in the back of the mind, as they are the most frequent cause of unilateral facial pain. Atypical facial pain is a diagnosis of exclusion, which should only be considered when all possibilities have been exhausted. Thus, trigeminal neuralgia is the probable diagnosis; however, the assessment should not be terminated here. Trigeminal neuralgia (TN) is classified as classic (CTN) and symptomatic (STN) depending on the presence or absence of an underlying cause. The neurological examination is often helpful in differentiating between the two; CTN presents with no neurological deficits (as in this patient) whereas STN is usually associated with hyperesthesia in the distribution of the 5th cranial nerve, along with other cranial neuropathies. An MRI scan is important to confirm this distinction. The normal scan here rules out a large number of secondary causes such as tumors and multiple sclerosis. MRA of the intracranial vasculature is also of benefit in detecting aneurysms, another cause of STN; this too is normal. Note that a nerve biopsy is not of diagnostic or prognostic value and is not indicated here; nor is CSF analysis indicated. Carbamazepine is the first line treatment for TN; as it is potentially hepatotoxic, a liver profile should be performed prior to initiation. Surgical therapy is usually a second line treatment in resistant cases, following unsuccessful medical therapy. Sumatriptan is mainly used in the management of migraine; while a few small-scale studies have assessed its use in TN, this is yet to enter general medical practice. Valacyclovir is not indicated in this patient.


Discussion

Trigeminal neuralgia (TN) is defined by the International Headache Society (IHS) as a unilateral disorder characterized by brief electric shock-like pains, which are abrupt in onset and termination, and limited to the distribution of one or more divisions of the trigeminal nerve. The right side of the face is affected more commonly than the left (ratio of 1.5:1) with the maxillary branch being involved the most and the ophthalmic branch the least. The annual incidence has been reported as 4.3 per 100,000 population, with a slight female predominance (1.7:1). The peak incidence is at 60 to 70 years of age. TN is classified by the IHS as either classic (essential or idiopathic) or symptomatic (STN). Although the pain is indistinguishable, in classic TN (CTN) there is no underlying disease causing the condition. It has been proposed that the symptoms are caused by demyelination of the nerves leading to erratic transmission of impulses. This demyelination is postulated to be due to compression of the microvasculature of the trigeminal nerve near its connection at the pons by an enlarged blood vessel, possibly the superior cerebellar artery. In STN, pain is due to a demonstrable structural lesion other than vascular compression. These include multiple sclerosis (MS) plaques, tumours, aneurysms, or chronic meningeal inflammation. MS is the commonest associated disease with STN. The etiology of TN is most likely multifactorial; although a questionable family clustering exists. Multiple other causes have been described, including amyloid infiltration, arteriovenous malformations, bony compression, and small infarcts in the pons and medulla. A strict set of criteria was defined by the IHS in 2004 to distinguish CTN from STN; one of the most important criterions for STN is the presence of a causative lesion which can be demonstrated by special investigations and/or exploration of the posterior fossa. TN is a clinical diagnosis and the history and examination remain essential tools. The pain is classically paroxysmal, lasting from a fraction of a second to 2 minutes, and described as intense, sharp, superficial or stabbing with pain free periods in-between the paroxysms. Talking, smiling, chewing, brushing the teeth, and shaving have all been implicated as triggers. Trigger zones/areas of increased sensitivity are present in one half of patients, and often lie near the nose or mouth. Not all patients with trigeminal neuralgia have trigger zones, but if present, they are nearly pathognomonic for the disorder. The examination in patients with CTN is generally normal. Sensory abnormalities in the trigeminal area, loss of corneal reflex, evidence of any weakness in the facial muscles or presence of neurological deficits should prompt the physician to consider STN or an alternative diagnosis. Studies have demonstrated that trigeminal (corneal) reflex testing can distinguish CTN from STN with a sensitivity of 96% and a specificity of 93%. Investigations are generally unhelpful for the diagnosis, but can distinguish between the classic and symptomatic forms. MRI imaging of the brain may demonstrate MS, tumors, or other causes of STN, and should be performed in the initial evaluation of all patients presenting with TN. Magnetic resonance angiography (MRA) can be helpful in locating a vascular compression; however, its sensitivity remains low. The initial treatment of choice is medical therapy. Surgical options should be considered in refractory cases or in patients who relapse on medical treatment. According to current evidence-based treatment guidelines, first-line therapy should be with carbamazepine (CBZ) or oxcarbazepine (OXC). The efficacy of CBZ is stronger than OXC, but the safety profile is better in OXC. Second-line drugs may be considered if CBZ or OXC are ineffective or not tolerated and the patient refuses neurosurgical treatment. These include lamotrigine, baclofen or pimozide. To date, baclofen has the strongest scientific evidence for efficacy in the treatment of TN next to CBZ. Pimozide is seldom used in a clinical setting now. Other medications used include phenytoin, gabapentin, topiramate, clonazepam, and valproic acid. Surgical procedures may be performed via a percutaneous approach or open approach. Open techniques include partial trigeminal rhizotomy and microvascular decompression. Microvascular decompression appears to provide the longest lasting relief, with persistent relief at 10 years in more than 70% of patients. Percutaneous techniques comprise glycerol injection, balloon compression, radiofrequency rhizotomy, and gamma knife stereotactic radiosurgery. Although less invasive, these techniques may not provide enduring relief and have a higher incidence of sensory loss, which may cause the patient significant discomfort and can be extremely difficult to treat.


Take home messages

  1. TN is a clinical diagnosis characterized by paroxysms of intense unilateral facial pain resembling electrical shocks in the area of one of the branches of the trigeminal nerve.
  2. Investigations are generally not helpful in diagnosis, but can distinguish the classic from the symptomatic form.
  3. The initial treatment of choice is with carbamazipine (CBZ) or oxocarbazipine (OXC).
  4. Surgical therapy should be considered in patients who are refractory or relapses to medical treatment.

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  1. Am Fam Physician. 2008 May 1; 77(9):1291-6: Trigeminal neuralgia: Krafft RM.
  2. BMJ. 2007 Jan 27; 334(7586):201-5: Trigeminal neuralgia and its management: Bennetto L, Patel NK, Fuller G.
  3. Clinics (Sao Paulo). 2009; 64(12):1225-6. doi: 10.1590/S1807-59322009001200014: Successful treatment of a resistance trigeminal neuralgia patient by acupuncture: Sert H, Usta B, Muslu B, Gözdemir M.
  4. Curr Neurol Neurosci Rep. 2012 Apr; 12(2):125-31. doi: 10.1007/s11910-011-0242-7: Surgical management of medically refractory trigeminal neuralgiaPollock BE.
  5. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008 Dec; 106(6):788-805, 805.e1-6. doi: 10.1016/j.tripleo.2008.05.033. Epub 2008 Jul 26: Operative treatment of trigeminal neuralgia: review of current techniques: Toda K.
  6. Ther Adv Neurol Disord. 2010 March; 3(2): 107–115: Treatment options in trigeminal neuralgia: M. Obermann.
  7. Trigeminal neuralgia and other facial pain: EBM Guidelines: 3.8.2010