Predicting longitudinal trajectory of bone mineral density in paediatric systemic lupus erythematosus patients

(1) To identify the average lumbar spine (LS) bone mineral density (BMD) trajectory in paediatric systemic lupus erythematosus (pSLE) patients, and (2) to identify predictors of BMD trajectory.

68 consecutive newly diagnosed pSLE patients prospectively followed in our lupus cohort with three annual dual energy x-ray absorptiometry (DEXA) examinations were studied. Low LS BMD was defined as z-score ≤-2.0. Baseline and longitudinal clinical features including disease activity, treatment and bone physiology markers were collected. Hierarchical linear modelling was used to model trajectory of LS BMD and identify predictors.

Women constituted 84% of the cohort and median age at diagnosis was 13.1 years. The mean LS BMD z-scores decreased over time (-0.42 at first, -1.02 at second and -1.11 at third DEXA). Initially 9% of patients had a low BMD, which increased to 19% by 3 years after diagnosis. 35% of patients deteriorated in BMD category from the first to third DEXA. LS BMD (adjusted by height-for-age z-score) followed a general deteriorating trajectory of -0.06 z-score/year from diagnosis. Increased rate of deterioration of BMD trajectory was predicted by pubertal status at diagnosis, increased interval cumulative steroid exposure and decreased weight z-scores.

The LS BMD of pSLE patients followed a general deteriorating trend over time and could be predicted by a combination of pubertal status at diagnosis, interval cumulative doses of steroids and weight z-scores. Interval cumulative steroid dose represents an important target that clinicians may modify to ameliorate deteriorating BMD trajectory over time.