To what extent do rheumatoid factor and anticitrullinated protein antibodies influence bone loss?

This paper studies whether anticitrullinated protein antibodies and rheumatoid factor have an additive effect (an increased effect when both are present together compared to when either is present alone) on bone erosions in rheumatoid arthritis. 

In rheumatoid arthritis, the presence of proteins like anticitrullinated protein antibodies and rheumatoid factor indicates a more severe disease. Anticitrullinated protein antibodies trigger bone loss. Rheumatoid factor is associated with bone loss. However, it is unclear how the presence of rheumatoid factor relates to anticitrullinated protein antibodies.  

The authors studied whether the association between rheumatoid factor and bone erosion depends on the presence of anticitrullinated protein antibodies. 238 patients with rheumatoid arthritis were included in the analysis. The presence or absence of anticitrullinated protein antibodies and rheumatoid factor was recorded. The number and size of bone erosions was assessed.

The highest number of bone erosions was found in patients with both rheumatoid factor and anticitrullinated protein antibodies. The average number of erosions per patient was 5.35 (in patients with both proteins; 112 patients), 0.67 (only rheumatoid factor present; 28 patients), 2.41 (only anticitrullinated protein antibodies present; 29 patients) and 2.49 (both proteins absent; 69 patients).

Patients who were positive for anticitrullinated protein antibodies had the highest average erosion volume. There were differences in erosion volume between patients with and without anticitrullinated protein antibodies. Erosion size was influenced by presence of rheumatoid factor only in patients with anticitrullinated protein antibodies.

The authors concluded that both anticitrullinated proteins and rheumatoid factor contributes to bone loss. The presence of both proteins has an additive effect on the number and size of erosions.

This was a short term study.