Gamma knife thalamotomy for disabling tremor: a blinded evaluation

Background: Gamma knife thalamotomy (GKT) has been used as a therapeutic option for patients with disabling tremor refractory to medications. Impressive improvement of tremor has been reported in the neurosurgical literature, but the reliability of such data has been questioned.
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\nObjective: To prospectively evaluate clinical outcomes after GKT for disabling tremor with blinded assessments.
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\nDesign: Prospective study with blinded independent neurologic evaluations.
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\nSetting: University hospital.
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\nPatients: Consecutive patients who underwent unilateral GKT for essential tremor and Parkinson disease tremor at our center. These patients were unwilling or deemed unsuitable candidates for deep brain stimulation or other surgical procedures.
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\nInterventions: Unilateral GKT and regular follow-up evaluations for up to 30 months, with blinded video evaluations by a movement disorders neurologist.
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\nMain Outcome Measures: Clinical outcomes, as measured by the Fahn-Tolosa-Marin Tremor Rating Scale and activities of daily living scores, and incidence of adverse events.
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\nResults: From September 1, 2006, to November 30, 2008, 18 patients underwent unilateral GKT for essential tremor and Parkinson disease tremor at our center. Videos for 14 patients (11 with essential tremor, 3 with Parkinson disease tremor) with at least 6 months' postoperative follow-up were available for analysis (mean [SD] follow-up duration, 19.2 [7.3] months; range, 7-30 months). The Fahn-Tolosa-Marin Tremor Rating Scale activities of daily living scores improved significantly after GKT (P = .03; median and mean change scores, 2.5 and 2.7 points, respectively [range of scale was 0-27]), but there was no significant improvement in other Fahn-Tolosa-Marin Tremor Rating Scale items (P = .53 for resting tremor, P = .24 for postural tremor, P = .62 for action tremor, P = .40 for drawing, P > .99 for pouring water, P = .89 for head tremor). Handwriting and Unified Parkinson's Disease Rating Scale activities of daily living scores tended to improve (P = .07 and .11, respectively). Three patients developed delayed neurologic adverse events.
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\nConclusions: Overall, we found that GKT provided only modest antitremor efficacy. Of the 2 patients with essential tremor who experienced marked improvement in tremor, 1 subsequently experienced a serious adverse event. Further prospective studies with careful neurologic evaluation of outcomes are necessary before GKT can be recommended for disabling tremor on a routine clinical basis.
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\nGamma knife thalamotomy (GKT) is a noninvasive method of surgical lesioning that may be suitable for patients with medical comorbidities not eligible for traditional surgical procedures. Some patients may also prefer to avoid an open operation or placement of hardware. However, GKT lacks the benefit of intraoperative electrophysiological confirmation of the target site and is associated with delayed benefit (typically several months or longer) owing to the time it takes for the radiation to functionally damage or destroy the targeted tissue. Gamma knife thalamotomy is usually performed for essential tremor (ET); it is performed less commonly for Parkinson disease (PD) tremor as it does not improve bradykinesia or other motor symptoms of PD.
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\nDespite some literature claims of significant benefit from GKT,1-5 proper blinded assessments are necessary to determine how useful the procedure is and the time it takes to benefit. Likewise, adequate assessment of possible complications6-8 needs to take place. Using blinded video assessments and activities of daily living (ADL) scores, we have analyzed the clinical outcomes in patients with tremor who underwent unilateral GKT at the Toronto Western Hospital. Complications of treatment were also evaluated.

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