Objective: To define the pattern of persistent antibody response in children with resolved Lyme arthritis.
Methods: From a cohort of 67 children with Lyme arthritis followed in our department since 1989, 19 were selected using these criteria: All patients (1) were asymptomatic; (2) had an ELISA titer < or = 1:160; (3) had been in treatment a minimum of 6 months. Their initial and late samples were assessed by Western blot and the pattern of reactivity was analyzed.
Results: The mean interval between treatment and last sample was 9.6 months (6-23). Analysis of the last sample showed that only 5/19 were negative by ELISA and 4/19 were at the cutoff limit (1:80). Only 6 patients had fewer than 4 reactive bands, 4 had 4 bands, and 9 had 5-11 bands on Western blot. The 41, 39, and 60 kDa were the most commonly observed reactive bands at last evaluation. 31 and 34 kDa bands, while relatively common in initial samples (36%), became uncommon (5%) on late samples. A significant finding was the absence of IgM reactivity in 18/19: 1/19 had 41 kDa reactivity. Only 4 patients had both ELISA (< 1:80) and Western blot tests negative (< 5 reactive bands).
Conclusion: All patients with resolved Lyme arthritis continue to show serologic reactivity beyond 6 months of therapy. 68% of the patients satisfy Western blot criteria for positivity in our laboratory. IgM reactivity to any antigen was minimal and IgG reactivity against the 41 kDa antigen, considered diagnostic of infection in initial samples by some laboratories, is very common (16/19).