Anti-RA33 Antibodies Are Present in Patients With Lyme Disease.

Background/objective: To determine if anti-RA33 antibodies, which can be seen in early forms of inflammatory arthritis, are present in patients with Lyme arthritis (LA).

Methods: Anti-RA33 antibodies were tested using a commercially available assay in patients with LA (n = 47) and compared with patients with erythema migrans who returned to health (EM RTH, n = 20) and those with post-treatment Lyme disease (PTLD) (n = 50), characterized by noninflammatory arthralgia, as an observational comparative study utilizing Lyme-exposed patients from various original cohorts.

Results: We found that anti-RA33 was present in higher proportions of patients with LA (23.4% vs. 0%, p = 0.001) and PTLD (12.0% vs. 0%, p = 0.040) than healthy controls. There was also a trend toward a higher percentage of anti-RA33 positivity in patients with EM RTH versus controls (10.0% vs. 0%, p = 0.080). There were no statistically significant differences among groups of patients with LA, PTLD, and EM RTH (p ≥ 0.567). There was also no difference in the proportion of patients with antibiotic-responsive LA compared with those with persistent synovitis after antibiotics, termed post-infectious LA, and there were no differences in clinical manifestations, musculoskeletal ultrasound evaluation (synovial hypertrophy, power Doppler, tendinopathy), or patient-reported outcomes based on anti-RA33 status.

Conclusions: This is the first study to identify anti-RA33 antibodies in patients with LA, though these antibodies did not identify a unique clinical subset of patients in this cohort. Unexpectedly, we found anti-RA33 antibodies at similar levels in patients with PTLD and EM RTH; further study is needed to determine the relevance of this finding.