Factors associated with bone mineral density loss in patients with spondyloarthropathies: A 4-year follow-up study

Objective: To explore the relationship between laboratory, functional, disease activity markers and bone mineral density (BMD) loss in patients with spondyloarthropathies (SpAs).
Methods: A cohort of 41 SpA patients were followed up for 4 years. Disease activity indices, spinal mobility and laboratory tests, BMD using were monitored at the baseline and 4-year follow-up. The 4% BMD loss at either of the proximal femurs was defined as significant.
Results: Over the 4-year study period, 27% of SpA patients experienced femoral BMD loss. Baseline BMD > 0.85 g/cm² (p = 0.011) was the baseline factor associated with BMD loss at 4- year follow-up. Several clinical and functional tests were helpful in identifying the BMD loss at follow-up: CRP > 15.6 mg/L (sens. 91%, spec. 70%), ESR > 29 mm/h (sens. 82%, spec. 73%), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) > 4.75 (sens. 91%, spec. 62%). At follow-up anti-TNFa treatment history, stable or improved lateral flexion and intermalleolar distance (NPV, accordingly, 95%, 88% and 87%), made BMD loss unlikely. Deterioration of the physician assessment of global disease activity (PAGDA) score from baseline to follow-up was a remarkable predictor of BMD loss (PPV = 0.83), while stable or improved score excluded the BMD loss (NPV = 0.83). According to multiple logistic regression analysis, baseline BMD value and follow-up CRP levels, when considered together, identify BMD status correctly in 85% of SpA patients (Nagelkerke R² = 0.676).
Conclusion: Baseline BMD, anti-TNFa treatment, PAGDA score, spinal mobility tests and disease activity markers are useful factors in predicting the BMD loss in SpA patients and can provide surrogate information on BMD status.