Trigeminal surgery: two targets better than one.
In a study of 50 patients with trigeminal neuralgia, researchers compared two radiosurgery techniques using a gamma knife, which uses more than 200 collimated beams of gamma radiation that converge into a single beam that damages or destroys target tissue. The surrounding tissue receives a much lower dose of radiation.
During the procedure, the patient's head is secured in a stereotactic frame. Stereotactic imaging of the head and target is performed and a treatment plan is developed with the help of a computer. The plan may consist of a number of "shots" or rounds of radiation that cumulatively apply the amount of radiation necessary.
Classical radiosurgery treatment for trigeminal neuralgia focuses a 4-cm beam of gamma radiation at the root entry zone of the trigeminal nerve, said Robert M. Levy, Ph.D., of Northwestern University, Chicago.
He and his associates compared the classical procedure with treatment using a two-target strategy in patients with trigeminal neuralgia. In the alternative approach, two 4-mm diameter spheres of intense gamma radiation, called isocenters, targeted two points along the trigeminal nerve; the targeted volume of nerve was about 200 cc, roughly twice that of the traditional approach.
The study included patients with traditionally defined trigeminal neuralgia (TN) and atypical trigeminal neuralgia (ATN). Patients with both types experience episodic bouts of sharp, stabbing pain, but patients with ATN can have a constant burning or aching sensation in between bouts of the sharper pain. Both groups of patients have normal sensory examinations, with the exception of triggers that elicit pain.
Of the 50 patients who were enrolled, 41 had reached 18 months of follow-up at the time of Dr. Levy's presentation. Of the nine patients who underwent classical treatment, four had TN and five had ATN. Of the 32 patients who underwent two-target treatment, 13 had TN and 19 had ATN.
At 2 weeks after treatment, 89% of patients in the traditional treatment group had at least 90% pain relief, compared with 97% patients in the two-target group. At 18 months, 55% of patients in the traditional group had at least 90% pain relief, compared with 91% of patients in the two-target group. The traditional approach also had a higher recurrence rate than the two-target approach.
"Side by side, there is probably a slightly better initial success rate with two isocenters compared to one, but the real difference is in the vigor of the response with better long-term pain control," Dr. Levy said, adding that longer follow-up is needed to better assess the two-center approach. The two-target treatment worked similarly well for patients with TN and for those with ATN. Patients with ATN have been excluded from several previous treatment studies.
Side effects and complications were comparable in the groups, he said.
Surgery is indicated for trigeminal neuralgia when there are unacceptable side effects to medication or the medication fails to provide adequate relief. Although it is difficult to compare published treatment studies because of differences in the definitions of typical trigeminal neuralgia, microvascular decompression has at most a 90% success rate, Dr. Levy said.
Likewise, radiofrequency lesion procedures have a success rate of 85%-90% at most. Gamma knife radiosurgery success rates have ranged from 60% to 80%, but success rates have been lower for the treatment of ATN.
BY KERRI WACHTER
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|Title Annotation:||Pain Medicine|
|Publication:||Clinical Psychiatry News|
|Date:||Dec 1, 2004|
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