Neurofilaments are essential components of the axon cytoskeleton. Neurofilament defects are suspected in several neurodegenerative conditions, and antibodies to neurofilaments have been found in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. Our main objectives were: (i) to determine the prevalence of anti-neurofilaments antibodies in patients with rheumatoid arthritis (RA) complicated by peripheral neuropathy; and (ii) to relate the clinical features of RA and peripheral neuropathy to anti-neurofilament antibodies.
In this study we used an ELISA technique to measure IgG antibody levels against three neurofilament polypeptides (NF-L, 70 kD; NF-M, 150 kD; and NF-H, 200 kD) in RA patients with peripheral neuropathy, and compared them with the antibody levels in uncomplicated RA controls and healthy volunteers.
Abnormal antibody levels to one or more of the neurofilament polypeptides were found in 9 (32%) of the peripheral neuropathy patients, but only in 3 (9%) of the RA and healthy controls. There were significant correlations between the levels of antibodies against the different neurofilaments; the cross-reactivity of some sera with different neurofilament proteins was also observed. There was no significant correlation between the levels of anti-neurofilament antibodies and measures of RA disease activity.
We conclude that a significant proportion of our RA patients with neuropathy had abnormal antibody levels to one or more neurofilaments and that the measurement of these antibodies may provide a useful diagnostic test.