The present research is an observational clinical study. The project aims to investigate astrocytic damage, assessed through biological findings such as an increase in GFAP level and/or MRI water index, in patients with NMOSD and its potential role in predicting demyelinating relapses or affecting disability outcomes. It will also explore predictors of astrocytic relapses, focusing on demographic, clinical, and immunological biomarkers like T cell responses, B cell repopulation, and cytokine levels. The goal is to identify unrecognized disease activity, providing insights for future research and clinical trials.

The study will involve 8 sites in Italy: 6 NMOSD clinical centers for patient enrolment and 2 centers for bioengineering and biological analysis. Centralized analysis of the MRI images of all patients enrolled in the clinical centers will be performed by the Neuroimaging Research Unit Fase 1 of San Raffaele Hospital. A total of 50 patients will be included and they will be followed for 12 months.

Comprehensive evaluation of patients, including clinical assessment, bioengineering evaluation, MRI, and blood samples, will be conducted at baseline, month 6, and month 12. To assess silent astrocytic relapses, a specialized evaluation will take place at months 3 and 9, including clinical analysis, blood samples to assess biomarkers like GFAP, a reduced MRI protocol to assess MRI water index, and bioengineering evaluation. In the case of a classical relapse, a dedicated visit will occur within 5 days of symptom onset, using the same evaluation protocol as at months 3 and 9 (MRI and biomarkers will be evaluated if not done in the month before).

Inclusion Criteria:

• Adult patients (age ≥18 years);
• NMOSD diagnosis with AQP4 IgG positive status assessed with a cell-based assay;
• Under rituximab treatment (standard of care) from at least 1 year and for not more than 5 years;
• Ability to provide written informed consent.

Exclusion Criteria:

• History of a clinical relapse or new/enlarging T2 lesion during the 6 months preceding the enrollment;
• Steroids treatment during 30 days before the enrollment;
• Any contraindication to MRI;
• Patients currently participating in a different clinical trial;
• Patients currently pregnant.

The study will include adult patients with NMOSD.