Background: The cytotoxic T-lymphocyte antigen-4 (CTLA-4) pathway acts as a negative immune regulator of T-cell activation and promotes self-tolerance. Case: We report the first case of biopsy-proven central nervous system inflammatory demyelination in the context of primary immunodeficiency and a novel CTLA-4 variant. Conclusion: This case has significant implications for the development of novel treatments for autoimmune conditions including multiple sclerosis and further emphasises the need for caution with clinical use of CTLA-4 immune checkpoint inhibitors in those with a history of inflammatory demyelination.

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