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Abstract & Commentary
Source: Sydow O, et al. Multicentre European study of thalamic stimulation in essential tremor: A six-year follow-up. J Neurol Neurosurg Psychiatry. 2003;74:1387-1391.
Deep brain stimulation (DBS) of the ventral intermediate nucleus of the thalamus is an effective procedure that markedly improves quality of life in patients with medication-refractory essential tremor. DBS of the thalamus is approved for the treatment of essential tremor, and Medicare, Medicaid, and most insurance companies cover the costs of surgery and office visits to adjust the stimulation parameters. An initial wave of enthusiasm greeted the approval of DBS. However, concerns have been raised about its long-term efficacy and about the risks of hardware failure and infection.
To address these questions, a consortium of European movement-disorder neurologists set out to enroll patients in a longitudinal clinical trial with long-term follow-up. Thirty-seven patients with severe essential tremor were refractory to primidone, propranolol, and/or benzodiazepines and underwent DBS of the thalamus. Patients with cognitive impairment, abnormalities on CT or MRI, or previous thalamotomy were excluded. Of the 37 patients, 19 patients were available for assessment of clinical symptoms and effectiveness of DBS pre-operatively and at the end of 6-year follow-up. Patients were evaluated prior to the operation and followed at 1-, 3-, and 6-year follow-up using the stimulator-on and stimulator-off state on the essential tremor rating scale.
Total tremor score in the stimulator-on vs stimulator-off state showed the same magnitude of tremor reduction at baseline and at 6-year follow-up. Similar effects were seen in measures of activities of daily living and in manual tasks such as writing, drawing, and pouring. Transient adverse events were common, particularly stimulation-induced paresthesias and dysarthria in patients undergoing bilateral stimulation. One patient suffered a thalamic hemorrhage, and 2 patients developed infections of the implanted hardware requiring reoperation.
This study addressed an important question facing neurologists who manage patients with moderate-to-severe essential tremor. Who should undergo the operation, and what is a reasonable expectation for long-term improvement? Even though essential tremor is progressive and action tremor worsens over time, the benefits of DBS were maintained in this study without loss off efficacy over a 6-year period.
Unfortunately, this study illustrates the limitations of longitudinal studies of older patients. Only 19 of 37 patients were available for serial follow-up, due to unrelated patient deaths, serious medical illness, or loss to follow-up. Evaluations were performed by neurologists who were not blinded to stimulator status, and no attempt was made to control for antitremor medications. As a result, there is an inherent bias to collect data on healthier patients. The effects of turning the stimulator on and off are usually obvious, and an unblinded rating introduces bias on the part of the physician and patient. Nevertheless, the message of this paper is that DBS for essential tremor is reasonably safe and effective for at least 6 years.
In discussing the risk of surgery, most surgeons will quote a figure of 1% as the risk of a serious operative or perioperative complication. The rate of hardware failure or infection is probably considerably higher. Taken together, although DBS is a major advance in the treatment of essential tremor, operative, perioperative, and infection risks continue to limit this procedure to patients in good health, with medication-refractory, disabling tremor. — Steven Frucht, MD, Assistant Professor of Neurology, Movement Disorders Division, Columbia-Presbyterian Medical Center, is Assistant Editor of Neurology Alert.