Microsoft word - 7-trigeminalneuralgia

Trigeminal Neuralgia and Persistent Idiopathic Facial Pain

Definition
Trigeminal neuralgia (TN) is a unilateral painful disorder that is characterized by brief, electric-shock-like pains, is abrupt
in onset and termination, and is limited to the distribution of one or more divisions of the trigeminal nerve. The
International Headache Society (IHS) differentiates between classical trigeminal neuralgia, often caused by microvascular
compression at the trigeminal root entry to the brainstem, and symptomatic trigeminal neuralgia, caused by a structural
lesion other than vascular compression.
Persistent idiopathic facial pain (PIFP), previously termed atypical facial pain, is a persistent facial pain that does not have
the characteristics of cranial neuralgias and cannot be attributed to a different disorder. The facial pain occurs daily and
persists throughout the day. Generally, it is limited to one particular area on one side of the face at disease onset, is deep
and poorly localized, and is not associated with sensory loss or other neurological deficits. Investigations including X-ray of the
face and jaws or cranial computed tomography (CT) or magnetic resonance imaging (MRI) do not demonstrate any relevant
abnormality. The pain may be initiated by surgery or injury to the face, teeth, or gums, but it persists without any
demonstrable local cause.

Epidemiology
TN and PIFP are rare diseases, and studies on their prevalences are scarce. Analyses of a few of the available studies
suggest that the prevalence of TN in the general population might be between 0.01% and 0.3%. The gender ratio of
women to men is approximately 2:1. TN can first appear at any age, but disease onset occurs after the age of 40 years in
over 90% of cases. The peak age of onset is between the ages of 50 and 60 years. Anxiety and depression, as well as
deterioration of quality of life, are common consequences of the disease. Other cranial neuralgias and PIFP are far less
frequent than TN. Data on their prevalence in the general population are not available.
Pathophysiology
Current opinion is that TN is caused by a proximal compression of the trigeminal nerve root close to the brainstem (root
entry zone) by a tortuous or ectasic blood vessel (an artery or vein), leading to mechanically twisted nerve fibers and
secondary demyelination, probably mediated by microvascular ischemic damages. These changes lower the excitability
threshold of affected fibers and promote inappropriate ephaptic propagation toward adjacent fibers. Thus, tactile signals
coming from the fast myelinated (A-beta) fibers can directly activate the slow nociceptive (A-delta) fibers, resulting in the
high-frequency discharges characteristic of trigeminal neuralgia.
The pathophysiology of PIFP is unknown. The available literature suggests that abnormal sensitization of the trigeminal
nociceptive system may play a crucial role in the development of PIFP.
Therapy
Medical treatment of TN is based on the use of antiepileptic drugs. First-line therapy should be carbamazepine (200–1200
mg/day) and oxcarbazepine (600–1800 mg/day), according to current evidence-based treatment guidelines. Second-line
treatment is based on very little evidence and includes add-on therapy with lamotrigine (400 mg/day) or a switch to
lamotrigine, baclofen (40–80 mg/day), or pimozide (4–12 mg/day). Other antiepileptic drugs have been studied in small
open-label studies. Treatment with phenytoin, clonazepam, gabapentin, pregabalin, topiramate, and valproate, as well as
tocainide (12 mg/day), has also been suggested as beneficial.
The treatment of choice for PIFP is tricyclic antidepressants such as amitryptiline (50–100 mg/day). Selective serotonin
and norepinephrine reuptake inhibitors (duloxetine, venlafaxine, and mirtazapine) are used as well.
Surgical Treatment
If medical treatment is not successful, surgical procedures should be considered. These include microvascular
decompression of the nerve/vessel contact or destruction of the Gasserian ganglion. Microvascular decompression
provides the most sustained pain relief, with 90% of patients reporting initial pain relief and over 80% remaining pain free
after 1 year, 75% after 3 years, and 73% after 5 years. It is, however, a major surgical procedure that entails craniotomy
to reach the trigeminal nerve in the posterior fossa. The average mortality rate ranges from 0.2% to 0.5%, and up to 4% of
patients suffer from major problems such as cerebrospinal fluid leakage, infarcts, or hematomas. The most common long-
term complications include aseptic meningitis (11%), sensory loss (7%), and hearing loss (10%).
Gasserian ganglion percutaneous techniques are destructive interventions that include radiofrequency thermocoagulation,
balloon compression, and percutaneous glycerol rhizolysis. Ninety percent of patients report pain relief following these
procedures. One year following radiofrequency thermocoagulation, 68–85% of patients are still pain free, but after 3 years
the percentage goes down to 54–64%, and after 5 years only 50% of patients are still pain free. The most common side
effects are sensory loss (50%), dysesthesias (6%), anesthesia dolorosa (4%), and corneal numbness with a risk of
keratitis (4%). Gasserian ganglion therapies require short-acting anesthetics and are primarily minor overnight procedures
with an extremely low mortality rate.
In gamma knife surgery, a focused beam of radiation is aimed at the trigeminal root in the posterior fossa. One year after
gamma knife surgery, 69% of patients were pain free without additional medication. After 3 years, 52% were still pain free.
The development of pain relief can be delayed (for an average of 1 month). Side effects include sensory complications in
6% that may develop with a delay of up to 6 months, facial numbness in 9–37%, which improved over time, and
paresthesias in 6–13%. Quality of life improves by 88%. The main disadvantage of gamma knife surgery is the cost, which
limits its widespread use and makes it a last-reserve option for patients who cannot undergo open surgery or who have
blood coagulation problems (e.g., patients who are taking warfarin).
References
[1] Cruccu G, Gronseth G, Alksne J, Argoff C, Brainin M, Burchiel K, Nurmikko T, Zakrzewska JM; American Academy of Neurology
Society; European Federation of Neurological Societies. AAN-EFNS guidelines on trigeminal neuralgia management. Eur J Neurol 2008;15:1013–28. [2] Gronseth G, Cruccu G, Alksne J, Argoff C, Brainin M, Burchiel K, Nurmikko T, Zakrzewska JM. Practice parameter: the diagnostic evaluation and treatment of trigeminal neuralgia (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the European Federation of Neurological Societies. Neurology 2008;71:1183–90. Copyright 2011 International Association for the Study of Pain

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