The purpose of this study is to demonstrate the superiority of propionic acid over placebo as add on treatment in multiple sclerosis (MS).

This is a single-center, double-blinded, randomized trial. One hundred multiple sclerosis (MS) patients will be randomly assigned in a 2:1 ratio to receive either 100 mg of propionic acid or a placebo over a period of 90 days. Outcome measures will encompass NfL and GFAP levels, fatigue scores, quality of life assessments, and physical examinations. Additionally, subgroup analysis will involve the evaluation of MRI and MEG data.

Inclusion Criteria:

• Diagnosis of multiple sclerosis (MS)
• Clinically and radiologically stable MS in the previous 3 months
• Age between 18 and 60 years
• Positive finding for oligoclonal bands (OCBs)
• Written consent
• Blood collection at the beginning and end of the study for routine parameter examination as well as sample preservation (especially for measuring propionic acid levels)
• Negative pregnancy test for female participants of childbearing age

Exclusion Criteria:

• Existing propionic acid supplementation
• Change in disease-modifying therapy (DMT) in the previous 4 weeks
• Existing severe systemic diseases
• Presence of other concomitant structural nerve diseases (e.g., polyneuropathy, brain tumor, strokes)
• High JCV titer under Natalizumab