The relationship between soft tissue swelling, joint space narrowing and erosive damage in hand X-rays of patients with rheumatoid arthritis.

Objectives: To test the hypotheses that the progression of joint space narrowing behaves differently from the progression of erosions and that clinically and radiologically assessed soft tissue swelling relates more to diffuse cartilage loss than to erosive damage.

Methods: Radiographs and clinical data were obtained from 28 patients in a prospective, multicentre, randomized, placebo-controlled trial of prednisolone 7.5 mg daily over 2 yr. Radiographic scoring included the Larsen score, joint space narrowing and soft tissue swelling. Clinical joint inflammation in the hands was assessed every 3 months and cumulative synovitis score over the period of study was then calculated for each joint. The placebo-treated patients and the prednisolone-treated patients were analysed separately. The Larsen scores were compared after log transformation [transformed score=log(10) (original score+1)]. Changes in Larsen scores and joint space narrowing scores were compared with the cumulative presence of clinical synovitis and radiological soft tissue swelling using the correlation coefficient.

Results: There was a difference in the rate of progression in the Larsen score between placebo- and prednisolone-treated patients, but there was no significant difference in the rate of joint space loss. In placebo-treated patients, measures of synovitis correlated more strongly with progression of joint space narrowing than with changes in the Larsen score. In prednisolone-treated patients there was no correlation between clinical synovitis and change in Larsen score (r=0.029) and only a slight and non-significant correlation with joint space narrowing (r=0.127). Radiographic evidence of soft tissue swelling remained correlated with joint space narrowing (r=0.279, P:<0.001) but was not correlated with change in Larsen score (r=-0.113, P:<0.001 for difference between correlations). The correlation between Larsen score progression and joint space narrowing seen in the non-treated patients was completely abolished in the glucocorticoid-treated group (r=-0.003).

Conclusions: The progression of joint space narrowing behaves differently from the progression of erosions. Prednisolone slows (or even stops) the progression of erosions (as assessed by the Larsen score) while making no difference to the progression of cartilage loss (as assessed by joint space narrowing). The results also suggest that synovitis, whether measured clinically or radiologically, is more closely related to diffuse cartilage loss than to erosion progression. Any link between synovitis and erosions is abolished by glucocorticoid therapy while the link between synovitis and cartilage loss is not, pointing to at least two different mechanisms for these observed radiological features.