GAMMA-KNIFE RADIOSURGERY AS A LESIONING TECHNIQUE IN MOVEMENT DISORDER SURGERY

Object. To increase knowledge of the safety and efficacy of the use of gamma knife radiosurgery in patients with movement disorders, the aut hors describe their own experience in this field and include blinded i ndependent assessments of their results. Methods. Fifty-five patients underwent radiosurgical placement of lesions either in the thalamus (2 7 patients) or globus pallidus (28 patients) for treatment of movement disorders. Patients were evaluated pre- and postoperatively by a team of observers skilled in the assessment of gait and movement disorders who were blinded to the procedure performed. The observers were not a ssociated with the surgical team and concomitantly and blindly also as sessed a group of 11 control patients with Parkinson's disease who did not undergo any surgical procedures. All stereotactic lesions were ma de with the Leksell gamma unit using the 4-mm secondary collimator hel met and a single isocenter with maximum doses from 120 to 160 Gy. Clin ical follow-up evaluation indicated that 88% of patients who underwent thalamotomy became tremor free or nearly tremor free. Statistically s ignificant improvements in performance were noted in the independent a ssessments of Unified Parkinson's Disease Rating Scale (UPDRS) scores in the patients undergoing thalamotomy. Of patients undergoing pallido tomy who bad exhibited levodopa induced dyskinesias, 85.7% had total o r near-total relief of that symptom. Clinical assessment indicated imp rovements in bradykinesia and rigidity in 64.3% of patients who underw ent pallidotomy. Independent blinded assessments did not reveal statis tically significant improvements in Hoehn and Yahr scores or UPDRS sco res. On the other hand, 64.7% of patients showed improvements in subsc ores of the UPDRS, including activities of daily living (58%), total c ontralateral score (58%), and contralateral motor scores (47%). Total ipsilateral score and ipsilateral motor scores were both improved in 5 9% of patients. One (1.8%) of 55 patients experienced a homonymous hem ianopsia 9 months after pallidotomy due to an unexpectedly large lesio n. No other complications of any kind were seen. Neuropsychological te st scores that were obtained for the combined pallidotomy and thalamot omy treatment groups preoperatively and at 6 months postoperatively de monstrated an absence of cognitive morbidity. Follow-up neuroimaging c onfirmed correct lesion location in all patients, with a mean maximum deviation from the planned target of 1 mm in the vertical axis. Measur ements of lesions at regular intervals on postoperative magnetic reson ance images demonstrated considerable variability in lesion volumes. T he safety and efficacy of functional lesions made with the gamma knife appear to be similar to those made with the assistance of electrophys iological guidance with open functional stereotactic procedures. Concl usions. Functional lesions may be made safely and accurately using gam ma knife radiosurgical techniques. The efficacy is equivalent to that reported for open techniques that use radiofrequency lesioning methods with electrophysiological guidance. Complications are very infrequent with the radiosurgical method. The use of functional radiosurgical le sioning to treat movement disorders is particularly attractive in olde r patients and in those with major systemic diseases or coagulopathies ; its use in the general movement disorder population seems reasonable as well.