Comprehensive evaluation of bone structural and microarchitectural changes in rheumatoid arthritis treated with baricitinib using HR-pQCT, imaging, and biomarker analyses.

OBJECTIVES

To comprehensively evaluate the effects of baricitinib on bone structure and bone-related biomarkers in patients with rheumatoid arthritis (RA) using high-resolution peripheral quantitative computed tomography (HR-pQCT).

METHODS

RA patients initiating baricitinib were enrolled in this prospective study. Bone structure in the second and third metacarpal heads was assessed using HR-pQCT at baseline and after 6 and 12 months. Synovitis, tenosynovitis, and osteitis were evaluated using ultrasound and MRI. Serum cytokines, chemokines, and bone-related biomarkers were analysed through a multiplex bead assay.

RESULTS

Fourteen patients with RA who initiated baricitinib were included in the analysis. No new bone erosions were detected during the 12-month period, and several pre-existing erosions showed partial repair. HR-pQCT revealed favourable trends in trabecular bone parameters, including increases in volumetric bone mineral density and trabecular thickness. Serum osteoprotegerin (OPG) significantly increased, while osteopontin (OPN) and interleukin-23 (IL-23) decreased, indicating suppression of the IL-23/Th17/RANKL axis and enhancement of bone preservation pathways. In addition, baricitinib modulated inflammatory mediators, including increased Eotaxin and decreased MCP-3. These changes were accompanied by improvements in synovitis, osteitis, and tenosynovitis assessed by multiple imaging modalities.

CONCLUSIONS

Baricitinib treatment inhibited the progression of bone erosions and also induced partial repair in some lesions, accompanied by improvements in periarticular bone microarchitecture. These favourable effects on bone structure were paralleled by beneficial modulation of bone-related and inflammatory biomarkers. Collectively, these findings indicate that baricitinib contributes to the prevention of joint destruction primarily through structural preservation, supported by parallel molecular mechanisms.