Interpretation of immunoblot in pediatric Lyme arthritis.

Objective: To determine the pattern of bands present on an immunoblot (Western blot) in children with Lyme arthritis.
Methods: Sera from 20 children with Lyme arthritis from an endemic area were assayed, and the results compared with those obtained in 162 control sera from the same area. The study was retrospective, serum bank based.
Results: Eighty-seven percent of control sera revealed no bands on immunoblot, and all had < or = 4 bands. All Lyme arthritis sera revealed > or = 5 bands (mean 8.4, range 5-13 bands). Bands of molecular weight 25, 28, 39, 47, 50, and 93 kDa were seen in patients and not in controls. There was no correlation between duration of arthritis or activity of arthritis at presentation and number of bands present.
Conclusion: Criteria were derived for a positive immunoblot based on the number and molecular weights of bands seen in our laboratory. These are the presence of 5 or more bands, of which at least one is an apparently specific band (25, 28, 39, 47, 50, or 93 kDa). Results of immunoblot are useful to confirm clinically suspected Lyme arthritis.