GLORIA GALLOWAY, MD, Associate Professor, Neurology, Children’s Hospital, The Ohio State University, Columbus.
Case report
A 43-year-old woman presented to her primary care physician complaining of an intermittent tingling and crawling sensation
of 2 weeks' duration along the left side of her face, over the cheek, and above the eye. Drinking or eating caused sharp,
lancinating pain that lasted several minutes. She denied headache, weakness, eye tearing, or visual changes. Family and medical
histories revealed no neuromuscular diseases or other neurological disorders. The patient had a desk job.
The neurologic examination revealed an area of hyperesthesia over the area of distribution in the complaint. No weakness,
ataxia, or sensory loss was noted, and all cranial nerve functions were normal. The general medical examination was unremarkable.
Serum blood chemistries and cell count, liver panel, antinuclear antibody, and ESR results were normal.
Most cases of trigeminal neuralgia, or tic douloureux, are due to focal compression of the trigeminal nerve root near the
pontine entry zone, typically by an overlying artery or vein.1 Less commonly, this disorder may be due to a primary demyelinating disease such as multiple sclerosis (MS) or, rarely, infiltrative
etiologies such as a tumor or amyloid or, even more rarely, pontine infarction.2 Trigeminal neuralgia occurs in approximately 1% of patients with MS, in whom demyelination of the trigeminal sensory fibers
causes attacks of neuralgia.3
The incidence of trigeminal neuralgia is 4 to 5 persons per 100,000, with onset most commonly occurring during middle age
or later. (Consider MS in younger patients who present with trigeminal neuralgia.) The attacks, characterized by intense lancinating
pain over the area of the affected nerve, tend to last weeks or months and recur months or years later.3 Triggers include sensory stimuli, eating, drinking, or washing the face. The pain of trigeminal neuralgia has been attributed
to abnormal or ectopic discharges in the demyelinated nerve root and ganglion. Animal studies and pathologic examination of
these demyelinated fibers support this etiology.4
Patients with idiopathic trigeminal neuralgia have normal findings on neurologic examination, although impairment in perception
of temperature and light touch over the affected area may be noted. The workup of trigeminal distribution pain should include
MRI to evaluate the pontine area for ischemia, demyelination, neoplasm, or other causes of impaired sensation.
Spectrum of treatment options
Numerous options are available to treat this painful condition. First-line treatment is pharmacotherapy. Consultation with
a neurologist is warranted if the diagnosis is uncertain or the neuralgia is unresponsive to pharmacotherapy. A neurosurgical
consultation should be considered following failure of trials of numerous drugs.
Pharmacologic treatments for idiopathic trigeminal neuralgia include anticonvulsants such as carbamazepine (the only drug
mentioned in this article that is specifically labeled for use in trigeminal neuralgia), oxcarbazepine, phenytoin, lamotrigine,
topiramate, and gabapentin; antispasmodics such as baclofen; antidepressants such as nortriptyline or amitriptyline; NSAIDs;
and combinations of these medications.
The sodium channel blockers carbamazepine, phenytoin, and lamotrigine reduce the excitability of the gasserian ganglion and
modulate presynaptic excitatory neurotransmitter release. The sodium channel blocker topiramate also acts on enhancing gamma-aminobutyric
acid (GABA) and GABA receptor actions. The membrane stabilizer oxcarbazepine may have comparable efficacy with carbamazepine
and is reported to have a lower associated risk of bone marrow suppression and hepatotoxicity.
Lamotrigine has been used in both trigeminal neuralgia and in the syndrome of SUNCT (short-lasting, unilateral, neuralgiform
headache attacks with conjunctival injection, and tearing).5 Centrally acting antispasmodics such as baclofen inhibit spinal reflexes. Nortriptyline and amitriptyline act by inhibiting
histamine, acetylcholine, and 5-hydroxytryptamine.
Although most patients can tolerate medical therapy, the adverse effects and waning effectiveness of the drug or drugs may
necessitate adjustments in the regimen.
When medical therapy fails—invasive approaches
An estimated one half of patients with trigeminal neuralgia whose symptoms do not respond to pharmacotherapy undergo some
form of surgical intervention, which ranges from microvascular decompression to percutaneous procedures. Surgical treatment
is associated with a low recurrence rate, often eliminating the need for long-term medication use.6
Microvascular decompression
is an invasive procedure involving a craniectomy with examination and repositioning of compressive vessels with stents; some
vessels may be electrocoagulated and divided. Complete relief was reported by 82% of patients and partial relief by 16% in
one long-term follow-up study of the procedure.7 Favorable results at 10 years have been reported by many centers.
Microvascular decompression may not attenuate symptoms in patients with long-standing symptoms—and therefore long-standing
demyelination. This situation may support earlier surgical intervention than has been traditional and may offer a reasonable
rationale for offering this treatment to patients with persistent or frequent symptoms or who do not gain relief after at
least 2 medication trials.
Complications associated with microvascular decompression include residual pain, facial weakness, postoperative hydrocephalus,
ipsilateral hearing loss, recurrent hemifacial tic, ipsilateral hemifacial spasm, and glossopharyngeal neuralgia.
Percutaneous procedures
such as thermal ablation, balloon compression, and destruction of the trigeminal root using glycerol rhizolysis each involve
a controlled trigeminal injury that creates a traumatic lesion of the trigeminal root or ganglion, causing sensory loss. These
procedures are less invasive than microvascular decompression. Numbness or dysesthesias are reported in more than 15% of patients
who undergo these treatments; greater sensory loss is associated with less frequent recurrence of pain. It appears that the
trigeminal ganglion neuronal function is also altered, since herpes simplex virus reactivation appears to be triggered in
many cases as a result of altered neuronal transcription.
Approximately 90% of those who undergo balloon compression—insertion of a balloon into the entrance of Meckel's cave with
use of a balloon pressure monitor—experience pain relief, but more than 50% of these patients report postoperative numbness.8 Although 60% of patients are free of pain 8 years after undergoing balloon compression, the rate of recurrence is approximately
26%.
Percutaneous radiofrequency thermocoagulation involves insertion of an electrode into the trigeminal ganglion under local
anesthesia, and C and A delta pain-carrying fibers are selectively damaged.8 A systematic review of 175 studies of ablative neurosurgical techniques for trigeminal neuralgia found that when compared
with glycerol rhizolysis and stereotactic radiosurgery, radiofrequency thermocoagulation was associated with higher rates
of complete pain relief, along with the greatest number of complications. Possible complications of thermocoagulation include
facial numbness and dysesthesias.
Other percutaneous modalities include peripheral nerve stimulation via implanted subcutaneous pulse generators. This particular
procedure has been associated with a decreased use of pain medication.9 Stellate ganglion blocks may be effective and have been reported useful in patients with cerebellopontine angle tumors.10 Noninvasive linear accelerator radiosurgery involves high definition neuroimaging with high doses of radiation to the trigeminal
nerve. MRI is used to identify the root entry zone of the trigeminal nerve. Its use in trigeminal neuralgia is considered
experimental.11
More recently, gamma-knife radiosurgery—in which gamma radiation is focused on the root entry zone in the pons to create a
destructive lesion—has been used successfully in trigeminal neuralgia.12 Evidence to support its use is inadequate, however, and the modality cannot be recommended until long-term studies and further
systematic review are completed. Potential adverse effects of gamma-knife radiosurgery include facial numbness, dysesthesias,
corneal irritation, vascular damage, hearing loss, and facial weakness; risk and frequency vary with the dose schedule and
target area.
Botulinum toxin type A has had some success in trigeminal neuralgia, providing relief that typically lasts several months
between treatments.It reduces muscle spasm by inhibiting acetylcholine release at the neuromuscular junction and may also
have analgesic qualities.13 Adverse effects are typically dose dependent and can include allergic reaction and muscular weakness at the injection site.
Case outcome
The patient's physician prescribed a trial of carbamazepine, 200 mg/d, increasing to 200 mg tid over the next week. At a 6-week
follow-up visit, if symptoms had progressed, the physician would consider a brain MRI scan along with neurologic consultation.
At 6 weeks, however, the patient's symptoms had improved considerably. No significant side effects had occurred, and the neurologic
examination was normal.
This article was contributed by Dr Galloway and edited by Julia M. Russell.
Dr Galloway discloses that she has no financial relationship with any manufacturer in this area of medicine.
REFERENCES
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Drugs mentioned in this article
Amitriptyline (Elavil, Endep)
Baclofen (Lioresal)
Botulinum toxin (Botox)
Carbamazepine (Tegretol)
Gabapentin (Neurontin)
Lamotrigine (Lamictal)
Nortriptyline (Aventyl, Pamelor)
Oxcarbazepine (Trileptal)
Phenytoin (Dilantin)
Topiramate (Topamax)
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