Permanent tremor reduction during thalamic stimulation in multiple sclerosis
- Wesley Thevathasan1,2,3,
- Patrick Schweder1,4,
- Carole Joint4,
- Nicola Ray1,
- Pieter Pretorius5,
- Ralph Gregory3,
- Tipu Aziz1,4
- 1Nuffield Department of Surgery, University of Oxford, Oxford, UK
- 2Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, Queen Square, London, UK
- 3Department of Neurology, John Radcliffe Hospital, Oxford, UK
- 4Department of Neurosurgery, John Radcliffe Hospital, Oxford, UK
- 5Department of Neuroradiology, John Radcliffe Hospital, Oxford, UK
- Correspondence to Dr Wesley Thevathasan, Department of Neurology, John Radcliffe Hospital, Oxford OX3 9DU, UK;
- Received 31 March 2010
- Revised 9 June 2010
- Accepted 17 July 2010
- Published Online First 30 September 2010
Background Unlike thalamic lesioning, thalamic stimulation is considered a reversible treatment for tremor. However, tremor in multiple sclerosis (MS) can sometimes permanently improve during thalamic stimulation. Such ‘permanent tremor reduction’ (PTR) has been attributed to limb weakness preventing tremor expression. In this study, 11 consecutive patients with MS tremor treated with thalamic stimulation were assessed for PTR. Eighteen upper limbs had tremor, of which 16 received contralateral stimulation.
Methods Tremor severity and limb strength were assessed preoperatively, early postoperatively (within 1 year) and late postoperatively (after 3 years). Tremor severity was rated using validated clinical scales both on and off stimulation. Following explantation, the parenchyma surrounding three electrode tracts was examined with MRI.
Results At final review (mean 5.2 years) PTR was evident in 11 of the 18 upper limbs with tremor. PTR often rendered stimulation redundant. PTR could occur when limb strength was conserved and could arise remotely from the initial surgery. PTR was significant (and universal) in limbs that received long-term (>2 years) effective (tremor suppressing) stimulation. PTR was not a significant finding in limbs that had not received long-term, effective stimulation. Contralateral to a limb with PTR, MRI revealed a thalamic lesion adjacent to the electrode tract. Thalamic lesions were not identified contralateral to two limbs without PTR.
Conclusions MS tremor often permanently improves during thalamic stimulation, even when limb strength is conserved. PTR may simply reflect natural history. Alternatively, these findings appear consistent with the recent proposal that thalamic stimulation in MS might promote local ‘demyelinative lesioning.’
Statistical analysis was performed by WT.
Funding The Oxford Biomedical Research Centre, The Medical Research Council, UK, The Charles Wolfson Charitable Foundation and the Norman Collisson Foundation.
Competing interests TA has received research funding and honoraria from Medtronic and St Jude's Medical.
Patient consent Obtained.
Ethics approval Ethical approval was obtained from Oxford REC.
Provenance and peer review Not commissioned; externally peer reviewed.