PERIPHERAL QUANTITATIVE COMPUTED TOMOGRAPHY-DERIVED BONE OUTCOMES AND RELIABILITY IN RHEUMATOID ARTHRITIS PATIENTS AND CONTROLS

Abstract

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease that affects the feet in up to 90% of patients, and can result in bone erosions. Little is known about disease activity at the metatarsophalangeal joints (MTPJs). Magnetic resonance imaging is used to visualize erosions, but does not provide quantification. Quantitative computed tomography (QCT) allows for differentiation between bone layers and quantifies volumetric bone mineral density (vBMD). We used a peripheral QCT (pQCT) scanner in MTPJs 2-5 in RA patients to determine reliability of a pQCT protocol, and then we determined the variability in vBMD between RA patients and controls. Patients (n=25) diagnosed with RA (2010 ACR criteria) were recruited from an academic Rheumatology clinic. Controls (n=27) were also recruited and matched for sex, age and ethnicity. Baseline MR data demonstrated that 80%, 64%, 40% and 20% of patients had erosions at MTPJs 2-5, respectively. One year later, MTPJs 2-5 were scanned using pQCT (XCT 2000); 2 transaxial slices were acquired per joint. A trained pQCT operator acquired 2 scans per participant with repositioning. Test-retest, intra- and inter-rater reliability were assessed blindly for total and cortical subcortical densities (mg/cm3). Reliability was reported as root mean square coefficients of variation (%RMSCV) and RMS standard deviation (RMSSD). The mean (SD) age and disease duration were 57.8 (10.2) years and 5.0 (0.9) years, respectively. Test-retest reliability was better for MTPJs 2 and 3, than MTPJs 4 and 5. Inter- and intra-rater reliability demonstrated high reproducibility. Total and cortical subcortical vBMD appeared lower in RA patients than controls. We have reliably determined vBMD using pQCT in MTPJs 2 and 3 in RA patients. The lower vBMD in MTPJ 3 suggests that RA patients may have true erosions at this joint. This research is in the early phases, but we hope to explore the correspondence between pQCT and other RA assessment tools.