Multiple sclerosis, chronic inflammatory disease of the central nervous system, affects approximately 100,000 peoples in France. It is the leading cause of disability in young adults. Tremor is a common symptom (25-58% of patients depending on the series) and can be particularly disabling. The drug treatments against tremor are ineffective or insufficient. Deep brain stimulation of the Vim (Small nucleus within thalamus) and stereotactic radiofrequency thalamotomy have shown their efficacy in this indication. However, in some cases these invasive procedures are impossible because of operational risk. Gamma knife thalamotomy can be an alternative choice. This procedure, less invasive, mainly because of the absence of craniotomy is used by several teams of international reputation for over fifteen years, with good to excellent results in essential tremor. The team of Marseille, which has an experience of 22 years in Gamma Knife radiosurgery has treated 250 patients with severe tremor (essential tremor or Parkinson's disease) by a unilateral thalamotomy with an improvement of 70% of functional scores.

In the literature, no formal studies of the effect of Gamma Knife in Multiple Sclerosis (MS) tremor is reported. There are only a few cases without specific evaluation of the efficacy in this disease. Hence the importance of studying in detail the effects of this technique, which allows a precise and limited lesion volume. Using an isocenter of 4mm and a dose of 130 Gy radiation lesion obtained is limited to a volume of 200 to 500 mm3.

The aim of this study is to assess through a minimally invasive technique with a circumscribed and reproducible lesion volume, the effect of thalamotomy on the particular tremor in multiple sclerosis with a prospective evaluation of its effects.

Patients with MS with a disabling tremor will be included in the study. They will be assessed with neurological examination, quality of life scales, neuropsychological assessment, functional scores and cerebral MRI.

This study will demonstrate the feasibility and effectiveness of Gamma Knife thalamotomy in MS patients with severe tremor.

Inclusion Criteria:

• Male or female aged 18 to 70 years old.
• Patient with a diagnosis of MS certainty according to the criteria of Mac Donald (2010)
• Patient with progressive form of MS: remitting, secondarily progressive, primary progressive
• Patient with an Expanded Disability Status Scale score (EDSS) between 3 and 8.
• Patient with clinical stability for more than 6 months (EDSS stable over 1 year)
• Lack of progressive onset (and corticosteroid therapy) for at least 3 months
• Patient with normal palliation or mild impairment
• Patient having a muscle test at 4 or 5 on the upper limb to be treated
• Patient requiring Gamma-Knife radiosurgery due to severity of tremor and functional impairment
• Patient who understood and signed the informed consent form

Exclusion Criteria:

• Stewart Holmes positive maneuver (upper limb to be treated)
• Patient with a muscle test less than 4 on the hand to be treated
• Patient with moderate palliation or severe disease
• Patient with a contraindication to perform a cerebral MRI (pacemaker, intracerebral metallic object etc.)
• Patient with an indication for radiosurgical treatment
• Pregnant or lactating women.
• Participation in another therapeutic trial or exclusion period from a previous clinical trial.