C4A and peeling skin syndrome: Compared with pSS patients without CNS involvement, those with CNS involvement showed higher prevalence of lung involvement (28.6% vs. 15.4%, p < 0.05), renal involvement (9.52% vs 0.2.4%, p < 0.05), ANA (95.2% vs. 71.1%, p < 0.05), anti-SSA positive (88.1% vs. 58.9%, p < 0.05), and lower levels of C3 (0.88 ± 0.30 vs. 1.05 ± 0.32, p < 0.05) and C4 (0.18 ± 0.06 vs. 0.23 ± 0.09, p < 0.05).