Background Non-radiographic axial spondyloarthritis (nr-axSpA) comprises the term in which patients may have clinical and laboratory features for SpA however do not have definite radiographic sacroiliitis but may have early MRI features on sacroiliac joints. Loss of bone mass in established ankylosing spondylitis (AS) is a known finding however bone status in very early disease stages is unclear.
Objectives To investigate bone mineral density in patients with nr-axSpA and to compare with age and sex matched patients with mechanical low back pain as controls. Also the relationship between disease activity, functional ability, quality of life, existence of inflammation at lumbar spine on MRI and vitamin D status in these patients were assessed.
Methods Patients aged between 18-45 years with chronic LBP with a history of no more than 3 years were consecutively recruited. The exclusion criteria were: other spinal disorders or spinal surgery, use systemic corticosteroids or biologics, prior diagnosis of osteoporosis, other disorders that may interfere with the bone metabolism. All of the patients were assessed for clinical features, anthropometric measurements (Bath AS Metrology Index), and Bath AS disease activity index (BASDAI) (0–10) and Bath AS functional index (BASFI) (0–100) and for ASAS axial SpA criteria.
Complete blood counts, ESR, CRP, HLA-B27 and serum levels of vitamin D [25(OH)vitD], calcium, phosphorus, alkaline phosphatase, parathyroid and thyroid hormones were assessed.
All of the participants underwent lumbar and pelvic X-ray. Lumbar and proximal femoral bone mineral density (BMD) measurements were made on the same advanced densitometer and sacroiliac and lumbar MRI was taken on a 1.5-T MR scanner. Patients who met criteria for ASAS but without definite sacroiliitis on pelvic X-rays were defined as nr-axSpA.
Results Forty-six patients (M/F,32/14) who met criteria for nr-axSpA and 29 (M/F,19/10) patients with mechanical LBP were included. All women in both groups were premenapousal. Tobacco use and number of gestation and delivery in women were similar between groups. Nr-axSpA group had restricted Schober’s test and chest expansion as well as poorer BASFI and higher BASDAI scores compared to the patients with mLBP. BMD values and T and Z scores at L1-L4 and L2-L4 were lower in nr-axSpA compared the patients with mLBP (p<0.05 for all) whereas BMD, T and Z scores were similar at the proximal femur. 25(OH)vit D levels as well as parathyroid hormone and thyroid functional tests were similar between groups.
Twenty (43.5%, 16 male) patients had bone edema (BO) on lumbar spinal MR indicating acute inflammation, whereas 26 (56.5%, 16 male) patients did not have. Comparison of BMD, T and Z scores between these patient subgroups (BO+ vs BO-) of nr-axSpA revealed that patients with inflammation (BO+) had reduced BMD at the lumbar spine and worse T and Z scores (p<0.0001) as well as worse BMD (p<0.001), T (p<0.001) and Z (p<0.01) scores at proximal femur (p<0.001).
Conclusions These results clearly show that patients with nr-axSpA had a significant bone loss in comparison to patients with mLBP at the lumbar spine and hip. MR data reveal that bone loss is closely related to the existence of BO on MRI indicating that inflammation causes low BMD in the very early stage of disease.
Disclosure of Interest None Declared