Predicting erosive disease in rheumatoid arthritis. A longitudinal study of changes in bone density using digital X-ray radiogrammetry: a pilot study

OBJECTIVE: Periarticular osteoporosis is one of the first radiological signs of rheumatoid arthritis (RA). Osteoporosis is now quantified using dual-energy X-ray absorptiometry (DXA), although it was originally assessed by radiogrammetry. A new updated system of radiogrammetry has been developed: digitized X-ray radiogrammetry (DXR). We used this DXR system to identify whether changes seen in hand X-rays of RA patients can predict those who subsequently develop erosions. METHODS: We enrolled 24 patients with early RA and they attended for hand radiographs at baseline, 12, 24 and 48 months. The hand radiographs were analysed using a Pronosco X-Posure system which measures bone mineral density, and other parameters using DXR. DXA of the hand was also performed to measure bone mineral density. Sharp and Larsen radiographic scores were calculated and other disease activity markers were measured. RESULTS: DXR bone mineral density fell significantly throughout the study. The group of RA subjects were divided according to the change in erosive status. Change in DXR bone mineral density after 1 yr was very specific (100%) and highly sensitive (63%) in predicting those who either became erosive or whose erosions significantly worsened. In contrast, of the other disease activity markers, only baseline ESR (sensitivity 67%, specificity 80%) significantly predicted the erosive status of subjects at 4 yr. CONCLUSION: Computerized radiogrammetry from digitized images can predict at 1 yr those patients with RA who will become erosive at 4 yr. A larger prospective study is required to confirm these findings; however, these results show some promise as a method of targeting those patients who require more aggressive, expensive therapy.