Characteristics of Patients with Guillain-Barré Syndrome and Fisher Syndrome in Complement Activation: A...

Introduction　Guillain-Barré syndrome (GBS) and Fisher syndrome (FS) are immune-mediated neuropathies in which complement activation may contribute to nerve injury. We investigated the clinical features associated with alternative and terminal complement pathway activation in GBS and FS.Methods　We retrospectively enrolled 40 patients with GBS and six with FS and measured pretreatment serum Ba and soluble C5b-9 (sC5b-9) levels. Complement levels were compared between the GBS and FS groups. In GBS, clinical features were compared between patients with sC5b-9 levels above and within the reference range, and associations with sC5b-9 were further assessed using logistic and linear regression analyses.Results　The serum sC5b-9 levels were higher in the GBS group than in the FS group, whereas the Ba levels were comparable. Elevated sC5b-9 levels were observed in 16/40 patients with GBS and in none of the six patients with FS. In GBS, elevated sC5b-9 was associated in unadjusted analyses with lower peak and 4-week Medical Research Council sum scores, less frequent ataxia, a higher frequency of anti-GM1 IgG positivity, and higher Ba levels. When sC5b-9 was analyzed continuously, a univariable linear regression analysis showed that higher sC5b-9 levels were negatively correlated with the peak Medical Research Council sum scores. However, peak muscle weakness, ataxia, and anti-GM1 IgG positivity were not independently associated with the sC5b-9 levels in the multivariable analyses.Discussion　Terminal complement pathway activation was observed in a subset of patients with GBS but not in this small FS cohort, despite similar alternative pathway activation. These findings suggest complement-mediated heterogeneity within the GBS-FS spectrum and support the prospective evaluation of sC5b-9 as a biomarker.