The incidence of TN is approximately 70 cases per 100,000 population. It most commonly occurs in people over 50 years old and is rarely seen prior to the age of 30 years.
If TN occurs in a younger patient, it almost always is associated with Multiple Sclerosis (MS). It occurs in females twice as often as in males. The pain is unilateral in 97% of the cases, and if it is bilateral it occurs in the same division of the nerve.
The second or third division of the nerve is affected in the majority of patients, with the first division affected < 5% of the time. The right side of the face is affected 57% of the time. The pain is characterized by paroxysms of electric shock-like pain lasting from several seconds to < 2 mins.
Many daily activities such as brushing the teeth, eating, shaving, or washing the face may provoke attacks and cause spasms of the facial muscles. This is why it is also called Tic-Douloureux. It is important to reassure patients that the pain can almost always be controlled.
TN occurs in many patients because tortuous aberrant blood vessels compress the Trigeminal Root. Acoustic Neuromas, Cholesteatomas, Aneurysms, Angiomas, and bony abnormalities may also lead to the compression of nerve roots. About 2-3% of patients with TN also have MS.
Therefore, coexistent MS should be considered in any patient under 50 y/o who presents with TN. The diagnosis is made by taking a careful history and physical exam. Tumors of the head and neck and MS must be ruled out.
The mainstay of treatment is PharmacoTherapy, and the first-line drug is Carbamazepine (Tegretol) (CARB). The usual rapid response to this drug essentially confirms a clinical diagnosis of TN. Baseline screening labs (complete blood count, urinalysis, and SMA-12) should be obtained before starting the drug.
Start with a 100-200 mg dose of CARB at bedtime for two nights and caution the patient regarding side effects, including dizziness, sedation, confusion, and rash. The drug is in equally divided doses over two days, as side effects allow, until pain relief is obtained or a total dose of 1200 mg daily is reached.
Careful monitoring of lab parameters is mandatory to avoid the rare possibility of life-threatening blood dyscrasia. At the first sign of blood count abnormality or rash, CARB should be discontinued.
Failure to monitor patients started on CARB can be disastrous, as Aplastic Anemia can occur. When pain relief is obtained, the patient should be kept at that dosage at least six months before tapering.
Routine Hematologic monitoring after stable dosage is reached is unnecessary. CARB blood levels should be obtained when non-compliance is suspected, when side effects occur at doses under 1200 mg, and when a 1200 mg/day dose is reached, to establish a baseline to allow safe titration of the dosage upward.
Phenytoin (Dilantin) may be used, but blood tests should also be obtained prior to therapy. A total dose of 300 mg is the goal, or until partial pain relief is obtained, and then carefully titrate the dose upward. Blood levels should be obtained pre-treatment, and side effects are similar to CARB.
Gabapentin (Neurontin) is a new AntiConvulsant that has shown some promise in the treatment of Neuropathic pain. It may be the next reasonable step for those patients not adequately treated with CARB or Phenytoin.
The drug is increased in 300 mg increments over two days as side effects (same as others) allow, until a total dose of 1800 mg daily is reached. Daily dose should not exceed 2400 mg.
Baclofen (Lioresal) may be of value for those patients not responding to the previous drugs. This drug has significant Hepatic and Central Nervous System side effects, including weakness and sedation. It is poorly tolerated by many patients.
Careful monitoring of lab values is indicated during the initial use of the drug. In treating patients with any of these drugs, the premature tapering or discontinuation of the medication may lead to the recurrence of pain and it will be more difficult to control pain thereafter.
The use of TN block with local anesthetic and a Steroid is an excellent adjunct to drug treatment. This technique rapidly relieves pain while oral medications are being titrated to effective levels.
The injection of small quantities of Glycerol into the area of the Gasserian Ganglion also provides relief for patients who have not responded to drug therapies.
The destruction of the Gasserian Ganglion by RadioFrequency is reserved for patients who have failed all other treatments and suffer from intractable TN.
MicroVascular decompression of the Trigeminal Root is the major neurosurgical procedure of choice for intractable TN.
The operation consists of identifying the Trigeminal Root close to the BrainStem and isolating the offending compressing Blood vessel, and interposing a sponge between the Vessel and Nerve, relieving the compression and the pain. This technique may be less successful in patients suffering from MS.
Proper identification of TN allows the patient prompt treatment with CARB while evaluation continues for presence of coexistent disease, including IntraCranial Tumor or DeMyelinating Disease.