Are Osteoporotic Fractures Preventable in Spondyloarthritis?

August 10, 2015

Up to one-third of people with active ankylosing spondylitis (AS) have some degree of bone loss due to systemic inflammation and decreased mobility, but lowering inflammation with tumor necrosis factor blockers may improve bone density.

Up to one-third of people with active ankylosing spondylitis (AS) have some degree of bone loss due to systemic inflammation and decreased mobility, but lowering inflammation with tumor necrosis factor blockers may improve bone density, recent studies suggest.

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In a review published online July 14, 2015 in the BMJ journal RMD Open, researchers from Descartes University in Paris, report that “treatments effective against inflammation have a positive effect on bone, and prospective open studies have shown that tumournecrosis-factor blockers can improve bone mineral density at the spine and the hip.” However, the researchers say, “There is so far no evidence of a decreased risk of fractures with such treatment.”

Ankylosing Spondylitis Effects on Bone

A case study published in the May 11 online issue of Clinical and Experimental Rheumatology, compared bone density scans of 504 ankylosing spondylitis patients - 417 men, 87 women, mean age 19, disease duration almost 8 years - with 106 age and sex-matched healthy controls.

Of the ankylosing spondylitis patients, 93 had added low-dose GCs (5-10 mg/day prednisone or equivalent) and 119 cases had been treated with conventional disease modifying anti rheumatic drugs (DMARDs).

Dual-energy X-ray absorptiometry (DEXA) scans were taken of the lumbar spine, proximal femur and forearm at the start of the study and every two years thereafter.

Those DEXA scans reveal that patients with ankylosing spondylitis had a higher prevalence of osteoporosis compared to controls (9.7% vs. 0%) and osteopenia (57.5% vs. 34.9%), researchers reported. One third of the patients with ankylosing spondylitis had normal bone mineral density, compared to 65% of controls. Cases with osteoporosis tended to be older, mostly male with longer disease duration; osteoporosis was more prevalent in the hip area.

Those with osteoporosis also had higher disease activity, body mass index (BMI), higher grades of sacroiliitis, higher erythrocyte sedimentation rates (ESR) and C-reactive protein (CRP), indicating greater inflammation, and also tended to be untreated. Osteoporosis tended to be more common in patients with syndesmophyte formation (bony growths) than those with a normal spine.

Of the 173 cases followed 1 to 5 years, low-dose systemic glucocorticoids in those with active disease did lower the disease activity but, interestingly, annual BMD changes were comparable between the glucocorticoids (GC) group and the non- glucocorticoids group.

“These results indicated that in active ankylosing spondylitis,  the benefits of low-dose GCs treatment on decreasing inflammatory bone loss by dampening inflammation may outweigh the risk of developing osteoporosis. Therefore low-dose GC treatment is beneficial for the treatment of AS and had few impact on bone mineral density,” the researchers wrote.

Resolving the Bone Paradox in Ankylosing Spondylitis

The exact mechanism and causes of bone loss in ankylosing spondylitis are not fully identified yet. In early disease, inflammation may play a dominant role, while in late ankylosing spondylitis, “bamboo” spine (resulting from vertebral fusion and bony growths) and ankylosis of hip joint result in decreased mobility, which may induce disuse osteoporosis, the authors wrote.

Patients with ankylosing spondylitis have both osteoporosis and an excess of bone formation (syndesmophytes). Vertebral fracture risk can be increased. Acute back pain patients is not always a flare-up of ankylosing spondylitis, since it can be related to bone complications. Those local changes and systemic bone loss are underpinned by different mechanisms.

There are no current guidelines for treatment of osteoporosis in ankylosing spondylitis. And low bone mineral density is found in early ankylosing spondylitis before any apparent structural changes.

For inpatients with an indication for tumournecrosis-factor blocker treatment, without prevalent non-traumatic fractures, “it seems logical to assess first the benefit of this treatment. However, in patients with severe osteoporosis and prevalent fractures, available guidelines in osteoporotic participants and male osteoporosis must be applied,” the authors of the study in Clinical and Experimental Rheumatology report.

References:

Briot K, Roux C. Inflammation, bone loss and fracture risk in spondyloarthritis. RMD Open, July 14, 2015, doi:10.1136/rmdopen-2015-000052.

Wang DM, Zeng QY, Chen SB, et al., Prevalence and risk factors of osteoporosis in patients with ankylosing spondylitis: a 5-year follow-up study of 504 cases. Clin Exper Rheum. 2015 Jul-Aug;33(4):465-70. Epub 2015 May 11.