Epilepsy is a disorder of the brain in which people have repeated seizures.

Autoimmune encephalitis (AE) is a rare cause of epilepsy. It is an inflammatory disease of the brain. This means that the body's own immune system attacks healthy brain tissue, just like it would if it were infected by a virus or a bacteria, by producing an army of proteins called 'antibodies' which go on to 'attack' healthy tissues.

Seizures in AE typically do not respond well to classic 'anti-seizure medications'. Instead, medications which suppress the immune system are used. These can have significant side-effects and some patients will still continue to have seizures or experience a recurrence of AE-related epilepsy despite treatment. It is difficult to accurately predict who will experience these outcomes.

This study aims to find ways of predicting and monitoring which people with AE are at greatest risk of these outcomes, so we can better direct them towards appropriate treatments. We will collect clinical information and samples of blood and cerebrospinal fluid (CSF, fluid surrounding the brain and spinal cord) from people with AE and 'control' participants with other neurological illnesses. Samples will be analysed for markers which may help predict or correlate with outcomes in AE and better understand this condition.

Inclusion Criteria:

• AE participants over the age of 18 will be recruited if they meet the criteria for clinically probable or clinically definite Autoimmune Encephalitis as per Graus and colleagues 2016.
• Neurological Control participants undergoing lumbar puncture as part of clinical care for other, non-encephalitis disorders (e.g. for investigation of headache where meningitis or encephalitis is not detected, for investigation and treatment of idiopathic intracranial hypertension) in Beaumont hospital will be recruited.

Exclusion Criteria:

AE participants

• Under 18 years of age
• Participants without AE or those with a definitive alternate diagnosis for presentation.

Other neurological control participants will be excluded if they have a current or historic diagnosis of AE.

Participants with probable or definite autoimmune encephalitis will be recruited via the Oxford Autoimmune Neurology Group in the UK and Beaumont Hospital in Ireland.

Data or samples may (with consent) be shared in coded format with other ethically approved research studies, relating to disorders of the nervous system.

Ethically approved studies which will process and dispose of data under the same regulations required by General Data Protection Regulation (GDPR) in Ireland and the European Union (EU).