TNF inhibitors aid AS bone density, but fractures remain a risk
Even with treatment, some axSpA patients had new, worsening spine fractures
Bone density increased significantly with long-term TNF inhibitor (TNFi) treatment for people with axial spondyloarthritis (axSpA), most of whom had ankylosing spondylitis (AS), a study suggests.
Despite the improvement, which could mean bones are becoming stronger, some patients continued to have new or worsening fractures in the spine, which researchers believe emphasizes the importance of monitoring for fractures in this patient population.
The study, “Improvement of bone mineral density and new vertebral fractures during 8 years of TNF-α inhibition in patients with axial spondyloarthritis,” was published in Seminars in Arthritis and Rheumatism.
AxSpA is a form of arthritis that causes inflammation and pain in the joints of the spine. AS is a common type ofaxSpA, where joint damage is visible on X-rays.
Poor bone-related outcomes are common in axSpA. For middle-aged patients, old bone tissue is broken down faster than new bone tissue is formed to replace it, leading to accelerated bone loss. Low bone mineral density (BMD), which causes bones to become weak and brittle, increases the risk of fractures that cause pain and disability.
While a loss of bone density, called osteopenia in earlier stages and osteoporosis when it’s more severe, happens naturally with aging, it’s much faster with axSpA.
TNFi are a class of anti-inflammatory therapies for treating axSpA. Because they come with some safety risks, they’re generally recommended for patients who have persistent disease activity on other standard treatments. Studies suggest TNF inhibitors can help slow bone density loss in axSpA, but long-term outcomes haven’t been evaluated.
Bone density gains; fractures still a risk
Here, scientists reviewed the long-term course of bone mineral density and spinal fractures among axSpA patients on TNF inhibitors. A total of 126 patients who’d been treated for at least eight years at medical centers in the Netherlands were included.
Most of the patients had AS (97%) and the TNF inhibitors used included etanercept, which is sold as Enbrel and biosimilars; infliximab, which is sold as Remicade and biosimilars; and adalimumab, which is sold as Humira and biosimilars.
As expected, overall disease activity decreased significantly with TNF inhibitors.
At the start of treatment, that is, its baseline, 34% had osteopenia in the lower spine and 7% had osteoporosis. In the hip, osteopenia and osteoporosis were observed in 29% and 2% of patients, respectively.
BMD progressively improved after starting TNF inhibitors. Specifically, spine BMD significantly improved relative to baseline over the first four years of treatment and hip BMD improved over the first two years. BMD generally stabilized up to year eight.
Particularly, BMD improved by a median of 8.9% in the lower spine after four years and by 7.2% after eight years. Hip BMD improved by a median of 2% at both times. After eight years, 92% had improved BMD in the lower spine and 67% had improved BMD in the hip.
While BMD increases are promising, they don’t “guarantee good quality of the bone,” wrote the researchers, who said more advanced techniques could be used in future studies to look specifically at changes in bone quality among axSpA patients.
Among 90 patients who had X-rays available at baseline and year eight, 20% had spine fractures at baseline. Over eight years of treatment, 16% developed at least one new spine fracture and existing fractures became more severe for 6%. Of 44 fractures detected after eight years, about 30% were considered moderate or severe.
Overall, fractures “seem to continue to develop and progress, irrespective of improvement in BMD,” wrote the researchers, who suggested that patients should be carefully monitored for fractures, along with bone density loss, in clinical practice.
One limitation noted about the study was the lack of data related to patients’ physical activity during follow-up. Physical activity is known to have beneficial effects on bone strength and can improve BMD in people with osteoporosis.
