Bone Changes Do Occur in PsA, Study Shows

Patients with psoriatic arthritis are at risk of systemic bone loss that does not show up using traditional scanning methods, new research finds.

​The study could help explain observations of low-trauma fractures in psoriatic arthritis patients, researchers wrote in the October issue of the Journal of Bone and Mineral Research. Using a high-resolution computed tomography technique, the research team found losses in the trabeculae of the radial bone in patients with psoriatic arthritis - changes not seen in healthy controls or patients with skin psoriasis alone. 

"We have to take care of both the joints and the bone with patients with PsA, because patients with PsA suffer from both local and systemic bone loss," said Roland Kocijan, the first author of the study and a physician at the Medical University of Vienna. "This is not reflected by standard measurements."

In fact, previous studies on psoriatic arthritis returned conflicting evidence on bone changes. Because the disease causes both bone loss and bone overgrowth near tendons and ligaments, teasing out the overall changes was difficult.

Kocijan and his team used high-resolution peripheral quantitative computed tomography (HR-pQCT), a strategy that gave them a resolution down to 82 microns in vivo. This technique allowed the researchers to assess cortical and trabecular bone independently. 

The researchers imaged the bones of 50 patients with non-axial psoriatic arthritis, 30 patients with skin psoriasis and 70 healthy controls, focusing on the ultradistal and periarticular radius. Compared to healthy controls, people with psoriatic arthritis had less trabecular bone mineral density, less trabecular bone volume, a lower trabecular bone number and increased trabecular separation. Bone mineral density, for example, was 162.1 +/- 39.8 milligrams of hydroxyapatite per cubic centimeter in psoriatic arthritis patients compared with 181.5 +/- 39 mg per cubic centimeter in healthy controls (p=0.021). Trabecular bone volume was down nearly 12 percent in psoriatic arthritis patients, from 0.151 +/- 0.03 bone volume over total volume (BV/TV) in healthy controls to 0.135 +/- 0.03 BV/TV in the arthritic patients (p=0.020).

The number of trabeculae was decreased 7.1 percent in psoriatic arthritis patients, from a trabecular number of 2.12 +/- 0.27 in healthy controls to a trabecular number of 1.98 +/- 0.31 (p=0.035). Trabecular separation was up 12 percent in arthritic patients, from 409 +/- 70 in healthy controls to 450 +/- 100 (p=0.028).

However, there were no changes in cortical bone between psoriatic arthritis patients and healthy controls. This contrasted with a 2014 study on rheumatoid arthritis by Kocijan and his colleagues. Those patients showed losses in both trabecular and cortical bone, Kocijan said, especially in cortical bone thickness.[[{"type":"media","view_mode":"media_crop","fid":"43495","attributes":{"alt":"©Lightspring/Shutterstock.com","class":"media-image media-image-right","id":"media_crop_8305370125453","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"4752","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"font-size: 13.008px; line-height: 1.538em; float: right;","title":"","typeof":"foaf:Image"}}]]

The lack of changes in cortical bone also contrast with a recent study of patients with psoriatic arthritis in China, published in the journal Osteoporosis International. In that study, researchers found no changes in trabecular bone in patients with psoriatic arthritis, but did find decreased cortical bone mineral density and porosity. Race likely plays a role in these contradictory findings, Kocijan said. Previous research has found thicker cortices and reduced cross-sectional area in Chinese-American women versus white women, as well as thicker trabeculae and less overall porosity, he said.

"Therefore, bone loss in Asian people is different from bone loss in Caucasians," he said.

Skin psoriasis alone did not seem linked to bone loss; patients with skin psoriasis and no arthritis had very similar bone values to healthy controls, Kocijan and his colleagues report in their new paper, which was published in the October issue of JBMR. But in patients with psoriatic arthritis, duration of skin symptoms was linked to the severity of bone changes, Kocijan said. This hints at a skin-bone axis at play in the disease, he said.

"It's all about the chronic inflammation," Kocijan said. In both skin psoriasis and psoriatic arthritis, the body overproduces inflammatory cytokines such as tumor necrosis factor-alpha and interleukin-17, both of which can affect bone structure and growth. If skin inflammation is affecting the bone, one might expect to see skin psoriasis patients experiencing bone losses, which this study did not find. However, Kocijan said, the skin psoriasis patients in the study had experienced their symptoms for 14 years on average, compared with 21 years on average for psoriatic arthritis patients. It's possible that bone damage from skin psoriasis simply takes longer to accumulate and thus wasn't detected in this current study.  Earlier research by Kocijan and his colleagues did find a higher rate of development of enthesophytes in patients with psoriasis but no psoriatic arthritis compared to healthy controls.

Regardless of the effects of psoriatic arthritis versus psoriasis alone, the new research hints at the potential for complications from the bone loss in psoriatic arthritis. Fourteen percent of the arthritic patients had a history of low-trauma bone fractures, the researchers found, while none of the participants in the skin psoriasis or healthy group had such a history. Similar results have been found in previous studies, Kocijan said. And the new research suggests that disease-modifying antirheumatic drugs may not do enough to prevent broken bones - there was no relationship between the occurrence of fractures and the use of these drugs or the use of glucocorticoids.

"We did not find any negative effects of those treatments on bone quality or quantity," Kocijan said. "But to be honest, there is only low evidence that there were positive effects on bone microstructure either … You cannot treat the systemic bone loss with anti-rheumatic drugs."

References:

1. Kocijan, R., Englbrecht, M., Haschka, J., Simon, D., Kleyer, A., Finzel, S., Kraus, S., Resch, H., Muschitz, C., Engelke, K., Sticherling, M., Rech, J. and Schett, G. (2015), Quantitative and Qualitative Changes of Bone in Psoriasis and Psoriatic Arthritis Patients. J Bone Miner Res, 30: 1775–1783. doi: 10.1002/jbmr.2521

2. Zhu TY, Griffith JF, Qin L, et al. Density, structure, and strength of the distal radius in patients with psoriatic arthritis: the role of inflammation and cardiovascular risk factors. Osteoporos Int. 2015 Jan;26(1):261–72.

3. Kocijan R, Finzel S, Englbrecht M, Engelke K, Rech J, Schett G. Decreased quantity and quality of the periarticular and non- periarticular bone in patients with rheumatoid arthritis: a cross- sectional HR-pQCT study. J Bone Miner Res. 2014 Apr;29(4):1005–14. 


4. Simon D, Faustini F., et al. Analysis of periarticular bone changes in patients with cutaneous psoriasis without associated psoriatic arthritis. Ann Rheum Dis. 2015 Feb 4. pii: annrheumdis-2014-206347. doi: 10.1136/annrheumdis-2014-206347. [Epub ahead of print]