The aim of this work was to examine the relationship between joint damage and monosodium urate (MSU) crystal deposition in gout.
Plain radiographs and dual-energy CT (DECT) scans of the feet were prospectively obtained from 92 people with tophaceous gout. Subcutaneous tophus count was recorded. The ten metatarsophalangeal joints were scored on plain radiography for Sharp-van der Heijde erosion and joint space narrowing (JSN) scores, and presence of spur, osteophyte, periosteal new bone and sclerosis (920 total joints). DECT scans were analysed for the presence of MSU crystal deposition at the same joints.
DECT MSU crystal deposition was more frequently observed in joints with erosion (OR (95% CI) 8.5 (5.5 to 13.1)), JSN (4.2 (2.7 to 6.7%)), spur (7.9 (4.9 to 12.8)), osteophyte (3.9 (2.5 to 6.0)), periosteal new bone (7.0 (4.0 to 12.2)) and sclerosis (6.9 (4.6 to 10.2)), p<0.0001 for all. A strong linear relationship was observed in the frequency of joints affected by MSU crystals with radiographic erosion score (p<0.0001). The number of joints at each site with MSU crystal deposition correlated with all features of radiographic joint damage (r>0.88, p<0.05 for all). In linear regression models, the relationship between MSU crystal deposition and all radiographic changes except JSN and osteophytes persisted after adjusting for subcutaneous tophus count, serum urate concentration and disease duration.
MSU crystals are frequently present in joints affected by radiographic damage in gout. These findings support the concept that MSU crystals interact with articular tissues to influence the development of structural joint damage in this disease.