The MYTH-MS study is a multicenter prospective study investigating the occurrence of clinical relapses in patients with relapsing-remitting multiple sclerosis (RRMS) in the absence of radiological activity on MRI.

While MS relapses are typically associated with gadolinium-enhancing lesions on MRI, some patients present with acute neurological symptoms without radiological correlates, referred to as acute clinical events with stable MRI (ACES). The frequency, mechanisms, and clinical relevance of these events remain unclear due to limitations in previous studies.

The primary objective is to determine the proportion of RRMS patients experiencing a relapse without gadolinium-enhancing lesions on early brain and spinal MRI. Secondary objectives include identifying clinical, radiological, biological, and psychological predictors, assessing neurologists' diagnostic accuracy, and evaluating clinical outcomes such as disability, cognition, and quality of life over a 6-month follow-up.

A total of 136 patients with recent neurological exacerbations will be included. Each participant will undergo clinical assessment, cognitive and psychological evaluation, and early MRI, with follow-up at 6 months. An ancillary study will explore blood biomarkers (NfL, GFAP, and circulating DNA) to help differentiate true inflammatory relapses from ACES.

This study aims to improve the understanding and diagnosis of MS exacerbations and to optimize patient management by reducing misdiagnosis and unnecessary treatments.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system characterized by relapses corresponding to episodes of new or worsening neurological symptoms. These relapses are typically associated with focal inflammatory activity detectable on magnetic resonance imaging (MRI) as gadolinium-enhancing lesions. However, in clinical practice, a subset of patients presents with symptoms suggestive of relapse without corresponding radiological findings, referred to as acute clinical events with stable MRI (ACES). The clinical significance, underlying mechanisms, and frequency of these events remain uncertain.

The MYTH-MS study is a multicenter, prospective cohort study designed to determine the proportion of patients with relapsing-remitting MS (RRMS) who experience a clinical relapse without gadolinium-enhancing lesions on early brain and spinal MRI. The study also aims to better characterize these events by identifying associated clinical, radiological, biological, and psychological factors.

Eligible participants are adults with RRMS presenting with recent neurological worsening suggestive of a relapse. At inclusion, patients will undergo standardized clinical evaluation, including neurological examination, disability assessment, cognitive testing, and patient-reported outcomes related to quality of life and psychological status. An early brain and spinal MRI with gadolinium injection will be performed within a defined time window following symptom onset.

The study will also assess the diagnostic performance of neurologists by comparing their clinical judgment regarding the presence of radiological activity and the likelihood of a true relapse versus a pseudo-relapse, along with their level of diagnostic confidence.

Participants will be followed for six months to evaluate clinical outcomes, including disability progression, cognitive performance, quality of life, and psychological parameters, and to assess the impact of relapse treatment according to MRI findings.

An ancillary biological study will be conducted to evaluate circulating biomarkers of neuronal and glial injury (e.g., neurofilament light chain [NfL], glial fibrillary acidic protein [GFAP], and circulating cell-free DNA). These biomarkers will be analyzed at baseline and follow-up to explore their potential role in distinguishing inflammatory relapses from ACES.

By providing a comprehensive characterization of MS exacerbations with and without radiological activity, this study aims to improve diagnostic accuracy, reduce uncertainty in clinical decision-making, and optimize therapeutic strategies in patients with RRMS.

Inclusion Criteria:

• Adult aged 18 to 70 years.
• Relapsing-Remitting Multiple Sclerosis according to the McDonald 2024 criteria.
• Patient receiving disease-modifying therapy (DMT) for multiple sclerosis.
• Most recent EDSS score between 0 and 7.0, dating back less than 1 year.
• Patient presenting with a neurological exacerbation lasting more than 24 hours and less than 7 days (excluding fatigue and pain alone).
• Patient capable of understanding the objectives and risks associated with the study and who has provided informed consent.
• Patient affiliated with or a beneficiary of a social security health insurance scheme.

Exclusion Criteria:

• Primary progressive or secondary progressive multiple sclerosis.
• Diagnosis of chronic psychotic disorder.
• Infection within the past week.
• Body temperature > 38.5°C at V0 (baseline visit).
• Corticosteroid bolus or plasma exchange in the month preceding inclusion.
• Chronic treatment with corticosteroids or immunosuppressants for another pathology.
• Contraindication to MRI or gadolinium.
• Uncontrolled cardiac, renal, or hepatic pathology.
• Patient participating in another interventional study or still within an exclusion period.
• Pregnant or breastfeeding woman.
• Severe claustrophobia.
• Patient deprived of liberty (e.g., incarcerated).