Systemic lupus erythematosus in childhood correlations between changes in disease activity and serum complement levels.

Serial complement component (C3 and C4) determinations were performed in 26 children with systemic lupus erythematosus. Twenty-one children with SLE had 52 episodes of C3 depression (mean duration 25 weeks); only 11 of these children had active nephritis when serum concentrations of complement were depressed. Fourteen children had active rash associated with low C3; in seven of these children rash was the only clinical evidence of disease activity. Ten children had active CNS disease; in seven children the CNS involvement correlated with low C3. In general, variations in serum concentrations of C4 did not reflect changes in SLE activity which were not reflected by changes in serum concentrations of C3. Serum C4 occasionally remained depressed longer than C3, perhaps reflecting continuing subclinical disease activity. Increased C3 occurred in 18 of 26 children as doses of corticosteroid were increased, in six of 14 when cyclophosphamide was added, and in two children when hydroxychloroquine was added. Our findings suggest that a wide variety of manifestations of childhood SLE may produce hypocomplementemia. In addition to renal disease, variations in serum concentrations of C3 and C4 can reflect, or occasionally predict, changes in rash and CNS disease.