Multiple sclerosis (MS), an inflammatory, neurodegenerative disease of the central nervous system, affects around 120,000 patients in France and is the leading cause of non-traumatic disability in young adults. It affects patients' health-related quality of life (QoL) and has a significant economic impact on patients and society as a whole. Early initiation of disease-modifying therapy (DMT) is recommended in relapsing-remitting MS (RRMS). Nevertheless, according to a recent French cohort, 30% of patients initially treated with a first-line FT will switch to a highly effective compound within 5 years due to its ineffectiveness. Therapeutic failure (Th-F) is therefore a frequent occurrence, but its psychological, social and economic consequences are poorly understood. These elements are generally the subject of measurements reported by patients, and several studies have highlighted the importance of taking them into account in the management of these patients.

Here, the investigators will study two categories of these measures in a Th-F situation. On the one hand, patient-reported outcome measurements (PROMs) will be examined. Patients' psychological distress and their QoL are two important examples of psychosocial impacts in patients with MS, compared to the general population. The impact on activity levels is also well known, but the specific effect of Th-F has not yet been studied. On the other hand, patients' experiences of their care pathway and their opinion on the quality of care (patient-reported experience measurement [PREM]) will also be studied. Some PREMs refer to care coordination, satisfaction with the relationship with carers or doctors' empathy levels. To date, data on the experience of MS patients regarding their care pathway remains limited and non-existent during Th-F.

Finally, the influence of socioeconomic status (SES) on PROMs and PREMs is worth considering. In the general population, patients' experience of care can be influenced by their socioeconomic status. Compared with research on other diseases (notably cardiovascular diseases and cancers), there is relatively little work on the association between socioeconomic status and MS and none has focused on the topic of Th-F.

The investigators therefore hypothesise that a quality of care perceived favourably by MS patients may moderate the negative impact of Th-F on their QoL, anxiety/depression and activity levels (as recently described in oncology), and a more recent measure of abilities assessing well-being defined in a broad sense, as a function of their SES.

Inclusion Criteria:

• Patient aged 18 or over.
• Patient with RRMS according to McDonald 2024 criteria.
• Uninterrupted use of a moderately effective treatment, or highly effective treatment only if it is the first DMT, for at least 6 months.
• Collection of non-objection.
• Patient affiliated to the social security system.

Exclusion Criteria:

• Patient with progressive MS.
• Patient treated continuously with the same DMT for 3 years or more.
• Patient who received a second line DMT or an immunosuppressant before taking a first line DMT.
• Patients who have received mitoxantrone as the first treatment
• Pregnant or breast-feeding woman at the time of inclusion.
• Severe cognitive and/or psychological disorders which, according to the investigator (with or without a neuropsychological assessment), prevent the participant from completing the self-questionnaires independently and accurately.

RRMS patients aged 18 or over with uninterrupted use of a moderately effective treatment, or highly effective treatment only if it is the first DMT, for at least 6 months.