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Multicentre European study of thalamic stimulation in essential tremor
  1. J P R Dick
  1. Department of Neurology, Greater Manchester Neuroscience Centre, Hope Hospital, Stott Lane, Salford M6 8HD, UK
  1. Correspondence to:
 DR J P R Dick; Jeremy.Dicksrht.nhs.uk

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Bilateral thalamic deep brain stimulation continues to show well maintained benefit in patients who have severe essential tremor after seven years with little increase in stimulation parameters

In their paper, Sydow et al (see this issue pp 1387–1391)1 have shown sustained long term efficacy of high frequency deep brain stimulation of the thalamus (Vim) for the management of severe essential tremor. This observation is of interest as certain authors had commented that its benefit may wane with time.2

A multicentre European trial had initially demonstrated the efficacy of thalamic deep brain stimulation (largely unilateral) in the management of essential tremor3 and a subsequent comparison of bilateral Vim stimulation with unilateral thalamotomy suggested that deep brain stimulation was more effective and certainly associated with fewer side effects.4 In the latter study the outcome was slightly better for essential tremor patients (using either procedure) than for patients with Parkinson’s disease or multiple sclerosis. At 6 months some tremor had recurred in 7 of 34 patients (3 Parkinson’s disease, 4 multiple sclerosis) undergoing unilateral thalamotomy and in 3 of 34 (1 Parkinson’s disease, 2 multiple sclerosis) undergoing bilateral deep brain stimulation; no tremor had returned in any of the 13 patients with essential tremor. The greater efficacy of bilateral thalamic deep brain stimulation for essential tremor is highlighted by Deuschl et al in their review.5 They comment that a bilateral procedure may have additional benefit for tremor of mid-line structures.5

In this study,1 37 essential tremor patients managed with bilateral thalamic deep brain stimulation were reviewed after one and six years. While there was a non-significant trend towards increased tremor after six years, an excellent functional improvement was still maintained when comparing both activities of daily living and tremor scores, ON and OFF stimulation. This trend would, of course, be consistent with the natural history of essential tremor. The observed increase in stimulator output during the six year period largely arose in the first year (2.0 to 2.3 V). The authors speculate that the subsequent increase (2.3 to 2.6 V) was a reflection of disease progression, although acknowledge that it may have reflected an element of tolerance.

They quote only one other study with a follow up period of equivalent length.6 In that study, 19 essential tremor patients were followed for six to seven years after unilateral thalamic deep brain stimulation. The benefits for postural and action tremor were well maintained over 6.5 years (SD 0.3) although, again, some slippage of effect was seen, for example for action tremor of the legs. The stimulator output increased from 2.0 V (SD 0.7), initially to 2.4 V (SD 0.9) after two years, and was 2.3 V (SD 1.0) after six to seven years.

These and other studies have shown that unilateral deep brain stimulation is as effective as unilateral thalamotomy in the management of severe essential tremor and it may be that bilateral deep brain stimulation is better than unilateral deep brain stimulation, particularly for those with a generalised tremor syndrome. Had there been poor durability of long term deep brain stimulation, the marginal superiority of stimulation over thalamotomy would have been lost, especially considering the cost and the more intense follow up regime required for deep brain stimulation. However, these two long term studies show well maintained symptomatic benefit over six to seven years, and any trend for recurrent tremor was scarcely detectable by statistics and may reflect the natural progression of the disease.

Bilateral thalamic deep brain stimulation continues to show well maintained benefit in patients who have severe essential tremor after seven years with little increase in stimulation parameters

REFERENCES

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Footnotes

  • Competing interests: JPRD was sponsored by Medtronic to attend a two day workshop organised by the European Continuing Medical Training Group, on deep brain stimulation in Keil, Germany, January 2003

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