CNS Inflammation as the First Sign of Complement Factor I Deficiency.

Complement factor I (CFI) deficiency is a rare autosomal recessive inborn error of immunity. In this report, we highlight that complete CFI deficiency may present with isolated and severe CNS inflammation without associated systemic features nor prior non-CNS episodes. This inflammation may respond to complement blockade therapy. This is a case description of a young girl with severe longitudinal transverse myelitis treated with aggressive immunotherapy that included eculizumab. Published cases of CFI-associated CNS inflammation were reviewed and discussed. A primary immunodeficiency panel revealed 2 germline pathogenic variants in the CFI gene. Further complement testing of the index case and her family confirmed complete CFI deficiency. We describe a unique case of severe spinal inflammation secondary to complete CFI deficiency. Although rare, isolated CNS inflammation may be the primary manifestation of complete CFI deficiency. To halt the uncontrolled complement-mediated inflammation associated with CFI deficiency, prompt targeted blockade of the complement pathway using eculizumab may be life changing in the acute phase. Long-lasting blockade of the complement pathway is also essential to prevent relapse in this subgroup of patients.