Serum complement levels in anti-N-methyl-d-aspartate receptor encephalitis

This study aimed to evaluate the relationship between serum complement and anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis.

Serum complement (C3, C4 and CH50), immunoglobulins (IgG, IgM and IgA) and C-reactive protein (CRP) were evaluated in 40 patients with anti-NMDAR encephalitis and 40 controls. Follow-up evaluations of 11 of the 40 patients with anti-NMDAR encephalitis were conducted 6 months after admission. Modified Rankin Scale (mRS) scores and clinical and cerebrospinal fluid parameters were evaluated in patients with anti-NMDAR encephalitis.

Serum C4 levels were significantly higher in patients with anti-NMDAR encephalitis than in controls (P = 0.003), especially in female patients (P = 0.001) and those with severe impairment (mRS ≥ 4; P < 0.001). Serum CH50 levels were significantly higher in patients with severe impairment (P = 0.007) and limited treatment responses (P = 0.007). Serum C4 was associated with C3 (r = 0.506, P = 0.001), CH50 (r = 0.478, P = 0.002) and mRS score (r = 0.607, P < 0.001). Serum C3 was associated with CH50 (r = 0.339, P = 0.032) and cerebrospinal fluid white blood cells (r = 0.351, P = 0.026). Serum CH50 was associated with age, mRS score and CRP. Follow-up evaluations revealed that mRS scores were significantly lower than those before treatment, and a significant negative correlation was observed between the change in C3 levels and the change in mRS score.

Our results demonstrated that serum C4 levels were elevated and associated with C3, CH50 and CRP levels, and disease severity in patients with anti-NMDAR encephalitis.