Permanent tremor reduction during thalamic stimulation in Multiple Sclerosis

Wesley Thevathasan (1) , Patrick Schweder (1) , Carole Joint (2) , Nicola Ray (1) , Pieter Pretorius (2) , Ralph Gregory (2) , Tipu Aziz (1)

1 AOPP - Department of Atmospheric, Oceanic and Planetary Physics [Oxford]
2 John Radcliffe Hospital [Oxford University Hospital]

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, eleven consecutive patients with MS tremor treated with thalamic stimulation were assessed for PTR. Eighteen upper limbs had tremor, of which sixteen received contralateral stimulation. Methods: Tremor severity and limb strength were assessed preoperatively, early postoperatively (within one year) and late postoperatively (after three 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 eleven of the eighteen 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, our findings appear consistent with the recent proposal that thalamic stimulation in MS might promote local 'demyelinative lesioning'.

Mots clés: MULTIPLE SCLEROSIS; STEREOTAXIC SURGERY; TREMOR

Wesley Thevathasan, Patrick Schweder, Carole Joint, Nicola Ray, Pieter Pretorius, et al.. Permanent tremor reduction during thalamic stimulation in Multiple Sclerosis. Journal of Neurology, Neurosurgery and Psychiatry, 2010, 82 (4), pp.419. ⟨10.1136/jnnp.2010.213900⟩. ⟨hal-00581009⟩