Background/Purpose:  Despite improvements in clinical management of rheumatoid arthritis (RA), many with early disease are still at high risk for developing periarticular erosions and osteopenia, as well as, generalized systemic bone loss.  It is essential to develop new approaches to assess changes in bone microstructure in people with early RA before permanent macro structural bone damage occurs. High Resolution Peripheral Quantitative CT (HR-pQCT) [XtremeCT, Scanco Medical AG] provides a solution; it is a novel imaging system that images bone microstructure at the thickness of a human hair.  The purpose of this study was to determine if HR-pQCT could identify and characterize early volumetric density or microstructural differences in people with early RA relative to controls.

Methods:  Thirty individuals with early RA and 30 age and gender matched controls consented to participate.  Five regions of interest (ROI) of the dominant side were imaged with HR-pQCT (82 μm, 60 kVp, 900 μA, 100 ms): ultra-ultra-distal radius (UUDr) [9 mm, starting 3 mm proximal to the medial tip distal radius]; metacarpal heads (MH) of the 2^nd and 3^rd digits [18 mm, starting 2 mm distal to tip of most distal 2^nd or 3^rd  MH]; and metacarpal shafts (MS) of the 2^nd and 3^rd digits [9 mm, starting 4.5 mm distal to 3^rd MS mid-shaft].

Standard manufacturer protocols were used for segmentation of the bone from the soft tissue. Cortical and trabecular regions were extracted using direct transformation methods with modified boundary conditions for the MH.  Primary outcome variables included: 1) whole, trabecular and cortical region apparent volumetric bone density (vBMD) and bone volume fraction (BV/TV), 2) trabecular region structural model index (SMI), 3) cortical region thickness (CtTh) and material vBMD, and 4) MS marrow space diameter (MSd).  Paired Student T-test statistical analyses were used to compare all variables.

Results:  Participants:  Both groups = Sex (Females 24, Males 6); age (mean 53 years, range 21 to 73).  RA group = 73% Rheumatoid Factor &/ or anti-CCP positive; mean 8 (SD 5) months since diagnosis and 13 (SD8) months since symptom onset and a Health Assessment Questionairre – Disability Index mean of 0.6 (SD 0.6).  Imaging:  HR-pQCT identified marked differences in whole, trabecular and cortical bone volumetric density and microstructure in the periarticular UUDr and MH regions, as well as, the extra-articular MS regions between RA subjects and controls.  All density and microstructural outcome variables were lower in early RA participants with the exception of UUDr and MH trabecular bone SMI and MSd, which were higher (Table 1).