Background/Purpose: Radiographic damage is frequently observed in patients with longstanding
gout.  Although cross-sectional studies have described factors associated with
joint damage in gout, there are very few prospective studies that have
investigated radiographic progression.  The aim of this prospective
observational study was to determine the rate of progression and factors
associated with progressive radiographic damage in gout.

Methods: People
with gout according to the 1977 ARA criteria, with disease duration <10
years were recruited into this prospective observational study.  At the
baseline visit, detailed clinical assessment was undertaken in 295 participants
including subcutaneous tophus count, joint counts, blood tests and plain
radiographs of the hands and feet.  Participants were invited to attend a
further study visit with repeat testing three years after the baseline visit.   Paired
radiographs (XR) were scored for erosion and joint space narrowing (JSN) in
chronological order by two readers according to the gout-modified Sharp van der
Heijde XR damage score.  Both readers were blinded to each other’s scores and
all clinical variables.  Inter-reader intraclass correlation coefficient (95%
CI) for the XR damage score was 0.91 (0.87-0.94).  The mean scores for both
readers were used in the analysis.  Pearson correlation and stepwise linear
regression models were used to identify variables independently associated with
progressive XR damage. 

Results: Paired
XR were available for 135 participants.  At baseline, mean (SD) erosion score
was 4.9 (10.2), JSN score was 6.0 (8.6) and total XR damage score was 10.9
(16.9).  At Year 3, mean (SD) erosion score was 7.7 (14.6), JSN score was 7.1
(9.7) and total XR damage score was 12.8 (19.2).  Change in subcutaneous tophus
count correlated with change in erosion score (r=0.36, p<0.001), change in
JSN score (r=0.33, p=0.001), and change in total XR damage score (r=0.53,
p<0.001). In stepwise linear regression analysis, baseline XR damage score and
change in subcutaneous tophus count independently predicted change in total XR damage
score over three years (model R²=0.48, p<0.001), with the
following baseline variables excluded from the model: tophus count, swollen
joint count, tender joint count, C-reactive protein, and serum urate.  Baseline
XR score and change in subcutaneous tophus count also predicted change in the XR
erosion and JSN scores when analysed as separate dependent variables in the
regression models.

Conclusion : The
presence of radiographic damage at baseline and development of new subcutaneous
tophi are associated with progressive joint damage in people with gout.  These
data provide further evidence that the tophus plays a central role in joint
damage in gout.