Background/Purpose: Ankylosing Spondylitis (AS) is not only characterized by pathological bone formation leading to ankylosis, but also by bone loss which may lead to vertebral fractures (VFx). TNF-alpha inhibitors (TNFi) have proven to be effective in blocking the inflammation process. A few studies also showed an increase of Bone Mineral Density (BMD) in AS patients treated with TNFi ^1-3 but the incidence of VFx after two years of treatment was increased.^3-4 To evaluate the long-term effect of TNFi on BMD and the incidence of VFx in patients with AS.

Methods: Consecutive TNFi naive patients diagnosed with AS according to the Modified New York criteria were included. Patients were recruited from the VUmc and the Amsterdam Outpatient clinic Reade and were treated with TNFi for 4 years. BMD at hip and lumbar spine (LS) were measured at baseline and after 4 years. T-scores were categorized as ‘normal BMD’, ‘osteopenia’ and ‘osteoporosis’, based on the WHO osteoporosis criteria.⁵ The incidence of VFx was determined by two observers using the Genant method.⁶

Results: In total, 107 AS patients with complete datasets (68.2% male) were included. The mean age was 42.6 years and the disease duration (time since diagnosis) was 11.0 years. At baseline 40.1% of the patients had a decreased BMD of the hip and 40.2% of the spine, of whom 27 patients (26%) had both a decreased hip BMD as well as a decreased lumbar BMD. The BMD of spine and hip improved after 4 years of TNFi treatment (Table 1). In 13 patients (12.1%), 14 VFx were observed both at baseline. After 4 years of TNFi-treatment 26 VFx were observed in 21 patients. After 4 years, 4 out of 21 patients with ≥1 VFx had a decreased BMD at hip and lumbar spine whereas the other 17 patients had a normal BMD. The majority of VFx was localized in the mid or lower thoracic spine.

Table 1: BMD measurement in spine and hip of 107 AS patients treated with TNFi.

*1 patient with spondylodesis; 4 patients with a total hip replacement

** 2 patients with spondylodesis; 5 patients with a total hip replacement

LS: lumbar spine, Abnormal BMD = osteopenia and/or osteoporosis according to WHO guideline⁶

Vertebral fractures (VFx)are presented in number of patients with a VFx and the actual prevalence of VFx. Outcomes are presented in n (%)

Conclusion: The percentage of relatively young AS patients with a decreased BMD at baseline of the hip and lumbar spine was high (40%). After 4 years of TNFi-treatment the BMD of the lumbar spine improved in 14.9% of the patients and of the hip in 8.3% of the patients. At baseline, several vertebral fractures were found and a few additional vertebral fractures were observed after 4 years of treatment.

References:

¹ Visvanathan S et al. Ann Rheum Dis 2009

²Arends S et al. Arthritis Res Ther 2012

³ van der Weijden et al. J Reumatol 2016

⁴Maas F et al. ClinExpRheumatol 2016

⁵Kanis JA et al. J Bone MinerRes 1994

⁶ Genant HK et al. J Bone MinerRes 1993

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/long-term-effects-of-tnf-alpha-inhibitors-on-bone-mineral-density-and-the-incidence-of-vertebral-fractures-in-patients-with-ankylosing-spondylitis-2/