Impact of disease activity on bone density, microarchitecture, and biomechanical properties in rheumatoid and psoriatic arthritis over 7 years.

OBJECTIVES: Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are chronic immune-mediated inflammatory diseases associated with progressive bone deterioration. Comparative longitudinal changes in bone density, microarchitecture, and biomechanical properties, and their association with disease activity, remain insufficiently elucidated in seronegative RA (RA-), seropositive RA (RA+), and PsA. METHODS: High-resolution peripheral quantitative computed tomography (HR-pQCT) was used to assess volumetric bone density (vBMD), microarchitecture, and biomechanical properties at the distal radius and the metacarpophalangeal (MCP) joint during routine follow-up. Generalised additive models, adjusted for age, sex, and body weight, were used to analyse the relationship between bone changes, diagnosis, and disease activity over time, spanning up to 7 years. RESULTS: We analysed 946 radius and 916 MCP scans from 482 patients (175 PsA, 221 RA+, and 86 RA-) over a mean ± SD follow-up period of 25 ± 27 months (maximum: 108) and 24 ± 30 months (maximum: 142), respectively. At all-time points compared, RA+ patients had lower trabecular vBMD than PsA (difference: 14.71 mg hydroxyapatite [HA]/cm³; 95% CI, 2.85-26.58; p = .003 at baseline) and RA- (difference: 16.92 mg HA/cm³; 95% CI, 0.97-32.86; p = .010 at baseline) patients. Longitudinally, total vBMD declined by -16.2 mg HA/cm³ (95% CI, -20.9 to -11.4; p < .001) in RA+ patients over 5 years, with smaller losses in RA- and PsA patients. PsA patients showed stable bone quality with cortical sparing; RA+ patients showed the most pronounced trabecular vBMD and microarchitectural loss; and RA- patients showed intermediate changes. Sustained remission preserved bone, while high disease activity was associated with deterioration. CONCLUSIONS: Longitudinal HR-pQCT shows site- and serostatus-dependent bone deterioration across inflammatory arthritides; RA+ patients have the worst trabecular changes, and those with PsA have relative cortical preservation. Sustained remission preserves bone structure and strength.