Over the past 20 years, doctors have gotten much better at spotting and treating brain conditions caused by the immune system attacking the body. These include illnesses like autoimmune encephalitis, ADEM, and multiple sclerosis. But even with better treatments, many patients-especially children-still struggle with long-term problems. Standard brain scans and tests often miss important issues like memory problems, emotional difficulties, trouble sleeping, and challenges with social behaviour. Early research using a special brain imaging technique (called MEG) has shown changes in brain networks that seem to be linked to poor memory. This study will use a new, advanced version of MEG that works even with very young children (as young as 2 years old). The goal is to better understand how these brain conditions affect children, compare them with other types of brain illness, and eventually use this technology to help predict outcomes and discover new ways to track brain health.

This study is an 8-year cross-sectional and observational cohort study involving the use of OPM-MEG, MEG, MRI and neuropsychology testing based at the Aston Institute of Health and Neurodevelopment, Birmingham, UK. Children and young people with immune and non-immune mediated neurological disease aged 2-15 years will be recruited locally (Birmingham Children's Hospital) and from London and Manchester.

The longitudinal cohorts (n=25 in each, total n=50) will be those with immune- and non-immune mediated neurological disease within 9 months of diagnosis. They will be invited for 3 study visits (Study Visits 1, 2 and 3).

The cross-sectional cohort (n=25) will be those with immune-mediated neurological disease at least 18 months after diagnosis. They will be invited to for one study visit (Study Visit 1).

The study visits:

At Study Visit 1 (Baseline), participants will undergo OPM-MEG, MEG and MRI as well as neuropsychology testing and questionnaire completion. Total time taken is 5 hours. This visit can be split into 2 visits within a 2 week window.

At Study Visit 2 (2 years)and 3 (5 years) participants will undergo OPM-MEG, MEG and MRI and questionnaire completion. Total time taken is 3 hours.

Participants travelling from outside the West Midlands will be offered overnight accommodation for Study Visits.

The participants are welcome to have as many breaks as is necessary during each/any Study Visit. It is expected that breaks will last between 15 minutes to one hour. Refreshments will be available for the participants on the day and will ask in advance of the visit in case of any allergies. Aston University, where the IHN is based, has food outlets Tesco, Greggs and Costa Coffee available too. Another adult, aside from the research team, can be present during the research recordings.

Inclusion Criteria:

• Individuals (age range 2 yrs to 16 years) who have received a diagnosis of immune-mediated neurological disease e.g. autoimmune encephalitis1, acute disseminated encephalomyelitis, multiple sclerosis. 2
• Individuals who have received a diagnosis of a non-immune mediated neurological disease (age range 2 yrs to 15 years 11 months) e.g. stroke.
• Patients who can give informed consent/ assent and have a person with parental responsibility capable of giving informed consent on their behalf if aged <16 years.

Exclusion Criteria:

• There is metal in the body or any other contraindication that precludes MRI scanning at IHN, or child usually requires sedation for clinical MRI scans.
• Participant dissents.

Data from this cohort may be highly valuable to future research efforts. Thus, we will ask participants to provide written informed consent to make their anonymised data freely available for reanalysis by the team in future studies, and to researchers outside of the study team for use in ethically approved projects. Specifically, neuroimaging (MRI), questionnaire, neuropsychology (summary scores) and demographic data that are suitable for sharing will be made available, using open-access data repositories platforms such as OSF (osf.org) or other suitable platforms which meet current best practice within the field, in relation to local and national regulations (i.e. GDPR). Open-access sharing of data will only happen once the linking document (linking study ID to personal identifiable data i.e. name) is destroyed (3 years after study end), to ensure that shared data is truly anonymous, not pseudo-anonymised

3 years after study end after linking document destroyed September 2037 to September 2047

Only the PI and study team