Fibromyalgia with elevated rheumatoid factor is associated with poor therapeutic response but not with progression to rheumatoid arthritis. Prospective cohort study.

Objetive: Evaluate response to treatment and progression to rheumatoid arthritis (RA) in patients with fibromyalgia (FM) associated with elevated rheumatoid factor (RF).

Material And Methods: Prospective cohort study. The sample consisted of 124 patients with FM: 62 with high RF (>20 U/mL) and 62 with negative RF (0-20 U/mL). All patients were evaluated using FM treatment improvement score (FIQR) and progression to RA according to EULAR/ACR 2010 criteria at 6 and 12 months. Pearson's χ test for homogeneity was used to relate variables of improvement to FM treatment and progression to RA.

Results: The response to treatment was lower in the high RF group (24 and 20 patients improved at 6 and 12 months, respectively, compared to 45 and 38 patients in the negative RF group), with a significant difference. Progression to rheumatoid arthritis was similar in both groups (5 in the high RF group and 4 in the negative RF group), with a non-significant relationship.

Conclusions: FM with elevated RF is associated with a poor therapeutic response but not with progression to RA.