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Inclusion Criteria:

* Probable relapsing-remitting MS (RRMS) according to Polman et al criteria 2010. or clinically isolated neurological syndrome (CIS) compatible with a demyelinating inflammatory episode within the central nervous system, potentially beginning multiple sclerosis (MS).
* Age 18-65
* EDSS before the current relapse \<6.5
* Acute relapse (optic neuritis, motor pyramidal relapse, cerebellar relapse, oculomotor relapse) since less than 2 months
* Having been treated by IV or orally steroid (Methylprednisolone, 1g/d for at least 3 days), followed or not by oral tapering.
* The current relapse inducing a significant clinical deterioration as compared to pre-relapse status and persisting 30 days after starting steroids.

  * Loss of visual acuity more than 30% on one ot both eyes;
  * Or: increase of 1 point pyramidal or brainstem functional system score (FSS) (if score ≥ 3) or cerebellar FSS (if score ≥ 2).
  * Or: reduced walking distance associated with an increase ≥ 0.5 point EDSS if EDSS ≥4.0;
* Having signed informed consent.
* affiliated to the French Social Security

Exclusion Criteria:

* Infection
* Improving relapse.
* Other disease interfering with evaluation.
* Current treatment by immunosuppressive drug (as cyclophosphamide and mitoxantrone) or interrupted for less than 3 months.
* Modification of DMT since less than 1 month.
* Physical or psychic disease interfering with evaluation or consent.
* Participation to another trial in the last 3 months.
* Inability to establish peripheral central intravenous access;
* Cerebral, autonomic, cardiac or other conditions with increased risk from hypovolemia
* Pregnancy or breast-feeding.
* Woman in age to procreate without effective contraception
* Treatment by monoclonal antibody.
* Progressive course of MS.

• Bordeaux, France
• Clermont-Ferrand, France
• Lille, France
• Nancy, France
• Nantes, France
• Strasbourg, France