Trigeminal neuralgia

Trigeminal neuralgia or (tic dolereaux) is characterized by intense, stabbing pain in the distribution of the trigeminal nerve.

The trigeminal nerve is mostly a sensory nerve its only motor function being the muscles of masctication. It is divided into the ophthalmic, maxillary and mandibular divisions. The three divisions join and form the Gasserion ganglion from which the trigeminal nerve root emerges and travels to the trigeminal nerve nucleus in the pons. One or all three divisions may be involved in trigeminal neuralgia.

The symptoms are usually unilateral. The patient may experience exacerbations with more frequent attacks, followed by remissions with fewer and les frequent attacks.

These patients usually are misdiagnosed with dental pain, sinus infections, eye pain, temporal-mandibular joint pain, temporal arteritis etc before an accurate diagnosis is made.

The most common cause of trigeminal neuralgia is irritation of the trigeminal nerve root by blood vessels. The most common culprit is the superior cerebellar artery. Other causes include multiple sclerosis, compression by tumor, or trauma.

Treatment:

1. Medications: Mostly involve anticonvulsants as a first line.

• Carbamezapine (Tegretol) – most significant reactions are: hyponatremia, agranulocytosis, and hepatic toxicity
• Oxycarbemezapine (Trileptal) – has fewer side effects than tegretol.
• Phenytoin (Dilantin) – Side effects include ginigival hyperplasia
• Baclofen
• Gabapentin

2. Surgical – usually attempted when medication fails

• Microvascular decompression (MVD)- aims to protect the trigeminal nerve root from vascular compression
• nerve lesion techniques – include balloon rhizotomy, microsurgical rhizotomy, gamma knife rhizotomy, radiofrequency rhizotomy, or glycerol rhizotomy. All these techniques involve creating a lesion and have a potential to exacerbate symptoms.
• Motor cortex stimulation – currently offered at very few centers.

Medical Management

A. The goal of pharmacologic therapy is to reduce pain.

B. Carbamazepine is regarded as the most effective medical treatment.

C. Additional agents that may benefit selected patients include phenytoin, baclofen, gabapentin, Trileptol and Klonazepin.

Invasive Non-Surgical

A. Peripheral Nerve Block. Provides temporary analgesia by injecting either phenol, or alcohol around the trigeminal branch involved.

B. Percutaneous Stereotactic Rhizotomy (PSR). The goal of PSR is to injure or destroy the trigeminal nerve via different techniques which may include radiofrequency thermocoagulation or glycerol injection.

In radio frequency heating, an electrode is inserted through a spinal needle under radiographic guidance and certain pain fibers of the trigeminal nerve are destroyed by heat. The major complication is called “anesthesia dolorosa” which is a painful condition that is difficult to treat. When this occurs the patient develops a severe constant burning, aching pain which is more disagreeable than the original pain. This occurs approximately 2 -4 % of cases.

With the glycerol injection a rhizotomy or nerve injury is performed by injecting glycerol in this same area instead of using heat. About 85-90% of patients have a good result – that is, significant relief from TN pain. With this procedure there is a lower incidence of “anesthesia dolorosa”.

Surgical

A. Microvascular decompression (MVD). The blood vessel that is pressing against the nerve is moved out of the way by tacking it up away from the nerve with Teflon felt and fibrin glue. The benefit of this procedure involves the fact that the problem itself is treated if in fact the blood vessel is the offending agent. There is an 85-90% initial success rate. The mortality for this procedure is 1%. The most common complications include mild facial numbness (25% – usually temporary), hearing loss on the affected side (3%), double vision (usually temporary), spinal fluid leak (5%), and meningitis (less than 5%)

B. Gamma Knife Radiosurgery (Radiation). This procedure involves targeting focused radiation to the trigeminal nerve thereby injuring it enough to keep it from firing the painful electric shocks. It is a good option for patients who cannot safely undergo general anesthesia or those who failed surgery on the blood vessel.