We tested the sera of 50 patients with
Lyme disease for
IgM-
rheumatoid factor (
IgM-RF) using a sensitive ELISA. Levels of
IgM-RF greater than 3 SD above the mean of normal subjects were found in 2 of 15 patients with
erythema chronicum migrans, 7 of 10 with neurologic abnormalities, and 7 of 25 with
Lyme arthritis (p = 0.038). Only 2 of these sera were positive by
latex agglutination. In contrast, none of the 23 control patients with
osteoarthritis,
ankylosing spondylitis, or
Reiter's syndrome had positive tests. The levels of
IgM-RF correlated with disease activity (p = 0.002), total serum
IgM levels (p = 0.002), and specific
IgM antibody titers to Borrelia burgdorferi (p = 0.006).
IgM-RF reactivity was absorbed with heat aggregated
IgG (HAGG), but the titer of specific
IgM antibody was insignificantly affected by this procedure. Thus, small amounts of RF are produced at certain times in many patients with
Lyme disease, and
IgM-RF production appears to be linked to the specific
IgM response.