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We read with interest the paper by Wishart et al.1 on chronic deep brain stimulation (DBS) for the treatment of tremor in multiple sclerosis. We would like to highlight two important points.
First, reduction in tremor should not be the ultimate goal of this surgery. It is a means to an end. The most important outcome for the patient must be improved function. Surgery that reduces tremor but does not improve limb function (for example, residual ataxia) is of questionable benefit for the patient, although surgeons may mistake it as “successful” if they only assess tremor. The authors’ review of the literature outlined many papers that focused on tremor but made no mention of function. In the authors’ own series of four patients, improvements in tremor “translated into improvements in aspects of daily functioning” but no details were provided on how this was measured. We addressed this point in a recent paper dealing with thalamic DBS for 12 patients with multiple sclerosis and tremor but unfortunately this was not included in the authors’ review.2
Second, the option of unilateral thalamic DBS in a patient with bilateral upper limb tremor should be discussed. We have found that, following DBS control of their dominant hand, some patients decide they do not need (or want) the other side done. If they have significant head tremor, however, bilateral surgery is required.3
We value Dr Berk and colleagues’ commentary and their input on the relevance of assessing limb function and its implications for quality of life. Our manuscript was written before their important contribution1 appeared in our literature search, and we regret that it was not included in our references. We targeted mainly English language outcome studies; an additional reference of note is that of Fernández-González and colleagues.2
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