Objective. To define the pattern of persistent antibody response in ch
ildren with resolved Lyme arthritis. Methods. From a cohort of 67 chil
dren with Lyme arthritis followed in bur department since 1989; 19 wer
e selected using these criteria: All patients (1) were asymptomatic; (
2) had an ELISA titer less than or equal to 1:160; (3) had been in tre
atment a minimum of 6 months. Their initial and late samples were asse
ssed by Western blot and the pattern of reactivity was analyzed. Resul
ts. 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 negati
ve by ELISA and 4/19 were at the cutoff limit (1:XO). Only 6 patients
had fewer than 4 reactive bands, 4 had 4 bands, and 9 had 5-11 bands o
n Western blot. The 41, 39, and 60 kDa were the most commonly observed
reactive bands at last evaluation. 31 and 34 kDa bands, while relativ
ely common in initial samples (36%), became uncommon (5%) on late samp
les. 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) an
d Western blot tests negative (<5 reactive bands). Conclusion. All pat
ients with resolved Lyme arthritis continue to show serologic reactivi
ty beyond 6 months of therapy. 68% of the patients satisfy Western blo
t criteria for positivity in bur laboratory. IgM reactivity to any ant
igen was minimal and IgG reactivity against the 41 kDa antigen, consid
ered diagnostic of infection in initial samples by some laboratories,
is very common (16/19).