084. THE PREDICTORS OF FRAGILITY FRACTURES IN PATIENTS ON ANTICONVULSANT THERAPY: AN OBSERVATIONAL STUDY

Abstract

Background: The use of anticonvulsant drugs has been associated with a low bone mineral density (BMD) and as a risk factor for fragility fractures in patients (ref). The FRAX tool uses the femoral neck BMD to predict fractures on a population basis but ignores the lumbar spine. Our objective was to determine the predictors of fragility fractures in an observational cohort of patients on anticonvulsant drugs. Methods: Patients referred for BMD estimation to a scanner in the North West of England between 2004 and 2014 on anticonvulsant drugs were identified from a dual X-ray absorptiometry (DEXA) database. Demographics and other risk factors, as well as fragility fractures, were recorded. Initially, those who had sustained a fracture were compared to those who had not sustained a fracture using chi squared test for categorical variables and t-test for continuous variables. Following that, univariate and multivariate logistic regression models were fitted looking at the predictors of fracture. Variables included age at scan, height, weight, alcohol, smoking, family history, rheumatoid arthritis, secondary osteoporosis as defined by FRAX, body mass index and steroid exposure, in addition to BMD in the lumbar spine and femoral neck. Results: 581 patients were scanned in the referral period. The mean age at scan was 59 (SD 12.78). 270 (46.5%) had sustained a fracture. Results of the univariate analysis are shown in Table 1. In the multivariate model, the variables that predicted fractures in this cohort were age at scan [odds ratio (OR) 1.03 (95% CI 1.02, 1.05)], femoral neck BMD [(OR 0.13 (95% CI 0.02, 0.76)] and lumbar spine BMD [OR 0.24 (95% CI 0.07, 0.82)]. Conclusion: In the univariate analysis, many risk factors are associated with fracture within this cohort of patients on anticonvulsant drugs, but both univariate analysis and multivariate analysis showed that lumbar spine BMD is a good predictor of fractures. This is not included in the FRAX tool and would underestimate the fracture risk in this cohort. Further modelling using lumbar spine BMD in other cohorts should be carried out to support this finding. (Table Presented).