TRIGEMINAL NEURALGIA

The incidence of Trigeminal Neuralgia is approximately 70 cases per 100,000 population. It most commonly occurs in people 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.

Idiopathic TN has four major characteristics:

a history of shooting, stabbing, jabbing, electric-shock pain in the distribution of the Trigeminal Nerve, which occurs in paroxysms Pain triggered by talking, chewing, kissing, drinking, brushing the teeth; A normal neurological exam Relatively pain-free periods between attacks

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.