Plasma C3c in immune-mediated neurological diseases: a preliminary report

Plasma C3c levels were examined in 56 patients with immune (27) and non-immune (29) mediated neurological diseases by crossed immunoelectrophoresis. Plasma samples were collected during the active phase of illness in both groups, usually within 7 days of admission. 11 patients (4 Guillain-Barré Syndrome-GBS, 3 chronic inflammatory demyelinating polyneuropathy-CIDP, 4 myasthenia gravis-MG) had their plasma saved sequentially during the active and the recovery phase. Plasma C3c levels were elevated in the group with immune mediated diseases when compared with those of non-immune mediated diseases. The sensitivity and specificity of C3c as a diagnostic test for immune mediated neurological diseases were 61.4 and 100% respectively with a positive and negative predictive value of 100 and 41%. the C3c levels in plasma correlated well with disease severity in MG and GBS patients. Such a correlation was also evident in all CIDP patients except one that had persistent elevation in the presence of clinical improvement. Results suggest that the plasma C3c level may be useful for differentiating immune from non-immune mediated neurological diseases. Plasma C3c may also be used for monitoring disease severity, particularly in myasthenia gravis.