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Trigeminal Neuralgia & Hemifacial Spasm (Part II)
The objective of treatment for trigeminal neuralgia is pain relief. While usual painkillers are not very effective, there are specific medications for this neuropathic pain. Developed for treating epilepsy, these drugs have proven to be effective for neuropathic pain as well. However, there might be side effects like fatigue or dizziness if it is started at high dose initially. Therefore, doctor usually starts with a low dosage, which can be gradually increased as the patient adapts to the medication. If the outcome is less than satisfactory with single medication, doctors may prescribe a combination of two or three medications.
Treatment for hemifacial spasm focuses on suppressing muscle twitching. Common oral medications include sedatives. They help patients stay relaxed and reduce the discomfort caused by hemifacial spasm. However, these medications do not directly control muscle contractions. Their effectiveness is often limited. In addition to oral medications, Botulinum Toxin type A (BtA) injections are also prescribed to reduce muscle spasms. As the effects typically last only two to three months, one may need to have repeated injection after about three months. It may also become less effective with time as the body develops drug resistance.
Q2. What are the effects of surgical treatment for trigeminal neuralgia?
If medication is ineffective for trigeminal neuralgia, interventional treatments can be considered. There are several options: firstly there is a neurosurgical procedure called “microvascular decompression”. Under microscope, the blood vessel causing nerve compression is identified and separated. A tiny piece of synthetic fibre is inserted between the blood vessel and the nerve. The piece of synthetic fibre acts as a cushion to avoid direct nerve stimulation from the blood vessel. Although it is an open surgery and performed under general anaesthesia, it requires no nerve cutting and causes no harm to other nerves if safely performed. Success rate in pain relief is around 80% to 90%.
Potential risk of this procedure includes hearing impairment if the acoustic (hearing) nerve is damaged. Therefore, doctors usually use intraoperative neurophysiological monitoring to closely monitor the nerves function during surgery to prevent these complications. If the patient is not fit for surgery or general anaesthesia, radiofrequency ablation or Gamma Knife surgery can be considered as alternative options. In radiofrequency ablation, an electric probe is inserted percutaneously to the trigeminal ganglion to destroy the nerve tissue. Although it is a less invasive procedure and does not require general anaesthesia, it causes damage to the trigeminal neuralgia, replacing the pain with numbness. If the sensation of cornea or eyelid is compromised, the protective blinking reflex may be lost or patient may not notice even if there is foreign body on the cornea. Therefore, this type of lesioning procedure is usually reserved for the patients of extreme age or physically not fit for surgery.
Gamma Knife surgery has also been introduced as a treatment option in recent years. With the same principle, it uses radiation (gamma rays) to cause local nerve destruction and reduce signal transmission. The drawback is that it takes time to become effective. On average, significant results are only noted after 6 to 12 months. Due to nerve destruction during treatment, one’s face may feel numb even if the pain is gone.
Q3. What are the surgical treatment options for hemifacial spasm? What are the effects?
If the effect of Botulinum Toxin type A (BtA) injection is not satisfactory, or if the patient does not want injections, doctors generally recommend microvascular decompression surgery. Under the operating microscope, the offending blood vessel is identified and separated from the nerve. A tiny piece of artificial fibre is then inserted between the vessel and nerve to protect it from being stimulated. The success rate is as high as 80% to 90%.
Rate of complete control may be lower if the hemifacial spasm has been existing for a prolonged period of time. The postulated reason is that irreversible damage of the nerve was established after prolonged period of compression. So it may continue to emit false signals and cause muscle spasms even the offending stimulus was removed. In some cases, severe tortuosity or atherosclerosis of the blood vessels can lead to excessive pressure on the nerves, which cannot be completely alleviated by the inserted cushion.
Likewise, the biggest risk involves the auditory nerve, since it is located very near the facial nerve. Both nerves must be monitored with extra caution to avoid any damage. In practice, the likelihood of this occurrence is only a few percent.
Q4. What are the precautions after surgery?
A few days of hospital stay are recommended after surgery to monitor wound healing and check for any signs of infection or other complications. Some patients may experience dizziness during the first two days, and are usually controlled by medication or subsided spontaneously. Since the surgical wound is located at the back of the neck, patients may feel stiffness and discomfort in that area during the first one to two days. This will also recover shortly.
The first two to three weeks after surgery are most critical. Patients should avoid vigorous exercise and weight lifting as the internal wound takes time to heal. This is also important for preventing cerebrospinal fluid leakage.
As with other open brain surgeries, it is generally recommended to avoid air travel for at least one month after the procedure. This is because air may have entered the brain during surgery, and expanded at high altitudes, which may then cause headache or even brain compression. Therefore, it is safer to wait for complete absorption of intracranial air.
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