Complement Factor I Deficiency With Acute Hemorrhagic Leukoencephalitis and Longitudinally Extensive Transverse Myelitis: A Case Report.

Objectives: Complement factor I (CFI) deficiency is a rare condition that can present with fulminant relapsing CNS autoinflammation. In this report, we highlight the utility of genetic testing in unexplained CNS autoinflammation.

Methods: This case report describes a young adult with partial CFI deficiency, presenting with acute hemorrhagic leukoencephalitis and longitudinally extensive transverse myelitis.

Results: In this case of unexplained CNS autoinflammation, in-hospital whole-genome sequencing and complement testing revealed partial CFI deficiency. CSF profiling during flares showed increased neutrophils and proinflammatory cytokines. CSF gene expression profiling more closely aligned with cases of bacterial meningitis than autoimmune encephalitis, consistent with innate immune system hyperactivity. Emergent IL-1 receptor antagonism led to sustained suppression of further immunologic attacks.

Discussion: Our case describes a presentation of CFI deficiency with fulminant and relapsing CNS autoinflammation. These flares were temporally associated with infections, which we hypothesize triggered innate immune overactivity due to CFI deficiency. Treatment with an IL-1 receptor antagonist, anakinra, suppressed further attacks and enabled neurologic recovery in a syndrome that is almost uniformly fatal. This case highlights the diagnostic value of inpatient genetic testing in cases of unexplained neuroinflammation and proposes targeted suppressive treatment to reduce neurologic deterioration.