Tremors can be quite debilitating for many patients with Parkinson's disease, essential tremor or multiple sclerosis. Medical therapy has some benefit, but the response can be variable or of limited duration. For patients with incapacitating tremor that is refractory to drug therapy, thalamotomy is effective for 73 to 93 percent of patients, but it carries a complication rate of 9 to 23 percent in patients with Parkinson's disease or essential tremor, and a complication rate of 16 to 41 percent in patients with multiple sclerosis. Bilateral thalamotomy has an even higher complication rate and is no longer performed. A newer alternative to ablative surgery is the use of deep-brain stimulation with an implantable electrode in the thalamus. Several studies have found this procedure to be effective and to have fewer complications than thalamotomy. Schuurman and colleagues conducted a randomized study to compare thalamic stimulation and thalamotomy in patients with refractory unilateral or bilateral tremor from Parkinson's disease, essential tremor or multiple sclerosis.
Patients enrolled were adults more than 18 years of age who had severe unilateral or bilateral tremor of the arm because of Parkinson's disease, essential tremor or multiple sclerosis. The symptoms had to be present for at least one year and refractory to medical therapy. Excluded were patients with cognitive dysfunction (Mini-Mental State Examination score: less than 24), advanced cerebral atrophy on computed tomographic scan, previous thalamotomy or medical contraindications to surgery (e.g., unstable cardiac or pulmonary disease, coagulation disorders). The patients underwent baseline testing with the use of three different rating systems to assess their individual stage of multiple sclerosis, essential tremor or Parkinson's disease. One month following these evaluations, patients with unilateral tremor were randomized to undergo an electrode implant or unilateral thalamotomy. Patients with bilateral tremor were randomized to undergo bilateral implantation of electrodes in one session or unilateral thalamotomy directed at the hand with the most severe tremor with contralateral electrode implantation performed six months later.
All patients were reassessed at three-month intervals for a total of 24 months following surgery. The primary outcome assessed was functional status based on a previously validated activities index. Secondary outcomes were the measure of the tremor of the arm, adverse effects, including change in cognitive status, and the patient's opinion of the surgical outcome. For this last component, patients were asked to numerically rate their preoperative and postoperative ability to perform complex activities.
Of the 175 patients referred for enrollment in the study, 68 patients were randomized into the trial after application of exclusion criteria. In the thalamotomy group, the mean age was 64 years, and in the thalamic stimulator group, it was 59 years. Of the 68 participants, 45 had a primary diagnosis of Parkinson's disease, 13 had essential tremor and 10 had multiple sclerosis.
The activities index scores from baseline to six months following surgery showed a mean increase of 31.4 to 36.3 in patients in the thalamic-stimulation group and 32 to 32.5 in the thalamotomy group. Thalamic stimulation resulted in consistently better improvement in function in patients with bilateral or unilateral tremor, Parkinson's disease and essential tremor, but not in patients with multiple sclerosis. Total or nearly complete suppression of the tremor occurred in 27 of 34 patients who underwent thalamotomy and in 30 of the 33 patients in the thalamic-stimulation group. At the six-month visit, 16 patients in the thalamotomy group had an adverse event compared with six in the thalamic-stimulation group.
The most frequent complications in both groups were gait or balance disturbances and dysarthria. The frequency of severe dysarthria and gait disturbances was much greater in the ablative surgery patients; however, one surgery-related death resulted from intracerebral hemorrhage in the second group. Patient self-assessment of functional status revealed that of the 34 patients in the thalamotomy group, only eight patients believed their functional status had improved, 22 patients reported no change and 4 patients reported that their condition had worsened. Of the 33 patients in the thalamic-stimulation group, 18 patients believed their functional status had improved, 13 reported no change and two reported that their condition had worsened.
The authors conclude that thalamotomy and thalamic stimulation are effective treatments for patients with severe tremors. However, the thalamic stimulator appears to provide greater functional improvement and to have fewer adverse effects.