Digital radiogrammetry as a new diagnostic tool for estimation of disease-related osteoporosis in rheumatoid arthritis compared with pQCT

Objectives: To investigate the potential of a new osteogeometric technology based on digital X-ray radiogrammetry (DXR) as a diagnostic tool for quantification of severity-dependent osteoporosis, and to distinguish between inflammation-mediated and corticoid-induced variations of bone mineralisation in patients suffering from rheumatoid arthritis. Methods: Ninety-six patients (duration of disease: <18 months) underwent retrospective calculations of bone mineral density (DXR-BMD) and metacarpal index (MCI) by DXR, which were calculated from plain radiographs of the non-dominant hand. For comparison, pQCT-calculated BMD (total, cortical-subcortical and trabecular partition of bone tissue) was done on the distal radius. Severity was classified using Ratingen Score by two independent radiologists, and divided into three main groups. In addition, the patients were separated into those with corticoid medication (n=44; 5 mg/day over a half year period) and a control group (n=52) without any corticoid therapy. Results: Correlations between DXR-BMD and MCI versus pQCT parameters were all significant (0.36<R<0.71; p<0.01), independent of corticoid therapy. Only in the group without corticoid application, the correlation between DXR-BMD and pQCT-BMD (cortical) showed no significant association. For patients with corticoid therapy, our data revealed the lowest correlation coefficient between DXR parameters and pQCT-BMD (trabecular). Without a difference in comparison to corticoid therapy, the significant relative decrease of BMD estimated by DXR between the highest and lowest score was between 11.1% and 14.3% and for MCI between 15.8% and 17.8%. The also significant relative decrease of trabecular BMD using pQCT varied from 10.3% to 16.9%, whereas no significant results could be verified for pQCT-BMD (cortical and total). Conclusions: Digital radiogrammetry can precisely estimate severity-dependent cortical reduction of bone mineral density in patients suffering from rheumatoid arthritis both with and without corticoid therapy, and seems to be able to distinguish the side effects of antirheumatic treatment from the disease-related periarticular bone loss. The detection and quantification of periarticular osteoporosis by DXR could be an important diagnostic tool in early rheumatoid arthritis.