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>0.85g/cm(2) (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>15.6mg/L (sens. 91%, spec. 70%), ESR>29mm/h (sens. 82%, spec. 73%), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)>4.75 (sens. 91%, spec. 62%). At follow-up anti-TNFα 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 R(2)=0.676).

Conclusion: Baseline BMD, anti-TNFα 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.