Serum concentrations of complement C3 and C4 in dogs with idiopathic epilepsy

Background: High concentrations of complement factors are presented in serum of animal epilepsy models and human patients with epilepsy. Objectives: To determine whether complement dysregulation occurs in dogs with idiopathic epilepsy (IE). Animals: The study included 49 dogs with IE subgrouped into treatment (n = 19), and nontreatment (n = 30), and 29 healthy dogs. Methods: In this case-control study, the serum concentrations of the third (C3) and fourth (C4) components of the complement system were measured using a canine-specific ELISA kit. Results: Serum C3 and C4 concentrations were significantly higher in dogs with IE (C3, median; 4.901 [IQR; 3.915-6.673] mg/mL, P <.001; C4, 0.327 [0.134-0.557] mg/mL, P =.03) than in healthy control dogs (C3, 3.550 [3.075-4.191] mg/mL; C4, 0.267 [0.131-0.427] mg/mL). No significant differences were observed in serum C3 and C4 concentrations between dogs in the treatment (C3, median; 4.894 [IQR; 4.192-5.715] mg/mL; C4, 0.427 [0.143-0.586] mg/mL) and nontreatment groups (C3, 5.051 [3.702-7.132] mg/mL; C4, 0.258 [0.130-0.489] mg/mL). Dogs with a seizure frequency >3 times/month had significantly higher serum C3 (6.461 [4.695-8.735] mg/mL; P <.01) and C4 (0.451 [0.163-0.675] mg/mL; P =.01) concentrations than those with a seizure frequency ≤3 times/month (C3, 3.859 [3.464-5.142] mg/mL; C4, 0.161 [0.100-0.325] mg/mL). Conclusions and Clinical Importance: Dysregulation of classical complement pathway was identified in IE dogs. Serum C3 and C4 concentrations could be diagnostic biomarkers for IE in dogs with higher seizure frequency.