Does serum rheumatoid factor have an influence on the clinical picture of ankylosing spondylitis?

To describe the influence of serum rheumatoid factor (RF) on the clinical and radiological picture of definite ankylosing spondylitis (AS).

In a retrospective chart review of 281 AS patients typed for RF, the clinical picture of RF positive patients (Group 1) was compared with RF negative patients (Group 2); mode of onset, disease duration, and treatment were recorded. All patients were examined to determine their clinical status; the blood cell count. HLA-B27, serum IgG, IgM, IgA, and erythrocyte sedimentation rate (ESR) were determined, and radiological studies of the entire spine, pelvis and affected peripheral joints were carried out. In patients from Group 1 the HLA-DR was also determined.

Fifteen of 281 patients (8 men, 7 women) with AS were RF+ (1:64 to 1:1024) (5.3%) and 11 were HLA-B27+. Seven patients in Group 1 had spine involvement and chronic arthritis of the knees. Four out of these 7 were tested for DR, and none was positive; in 6, AS and rheumatoid arthritis (RA) coexisted, 2 were DR1 and 2 were DR4 (test not carried out in 2). In two others we found spinal involvement only, and one of them had both DR1 and DR4. The onset of AS was similar in both groups. Group 1 was characterized by a chronic disease of moderate intensity with chronic arthritis of the metacarpophalangeal and proximal interphalangeal joints (p = 0.0008 and p = 0.04, respectively), no valvulopathy (p = 0.04) and fewer uveitis sequelae (p = 0.007) than Group 2. The ESR (p = 0.01), IgG (p = 0.008) and IgM (p = 0.0001) were higher in Group 1 than in Group 2.

The presence of RF in AS is associated with a chronic disease of moderate intensity with chronic peripheral arthritis and fewer extra-articular manifestations. The presence of RF, not always associated with HLA-DR, seems to affect the course of AS and does not necessarily indicate an association with RA.