Predictors for longitudinal trajectory of Bone Mineral Density in Pediatric Systemic Lupus Erythematosus Patients
Susanne Benseler, The Hospital for Sick Children 
Martin Charron, The Hospital for Sick Children 
*Lily Siok Hoon Lim, The Hospital for Sick Children 
Earl Silverman, The Hospital for Sick Children 
Pascal N Tyrrell, The Hospital for Sick Children 

Keywords: child, adolescent, lupus, bone mineral density

Pediatric Systemic Lupus Erythematosus (pSLE) is a rare chronic autoimmune disease involving multiple organs. Chronic inflammation from disease activity and treatment with steroids have potential detrimental effects on bone mineralization. Childhood and adolescence are important periods of bone mass accrual- critical to the attainment of peak bone mass- a factor believed to be an important determinant of future osteoporosis. As such, children with pSLE are a group at risk of future osteoporosis due to multiple insults on bone mineralization during this critical growth period. No previous study has evaluated the longitudinal trajectory of bone mineral density (BMD) in this population. Objectives: 1) To identify the average lumbar spine (LS)BMD trajectory in pSLE patients and 2) To identify predictors of BMD trajectory. Methods: 68 consecutive newly diagnosed pSLE patients prospectively followed in our Lupus cohort with 3 annual Dual Energy X-ray Absorptiometry (DEXA) examinations were studied. Low lumbar spine (LS) BMD was defined as z-score = -2.0, referenced to gender, age-norms. Baseline and longitudinal clinical features including disease activity, treatment and bone physiology markers were collected. Hierarchical Linear Modeling (HLM) was used to model trajectory of LS BMD and identify predictors. Results: Females constituted 84% of the cohort and median age at diagnosis was 13.1 years old. The mean LS BMD z-scores decreased over time (-0.42 at 1st, -1.02 at 2nd and -1.11 at 3rd DEXA). Initially 9% of patients had a low BMD, this increased to 19% by 3 years after diagnosis. Thirty-five percent of patients deteriorated in BMD category from the 1st to 3rd DEXA. Only 6% improved in BMD category by the 3rd DEXA. LS BMD (adjusted by height-for-age z-score) followed a general deteriorating trajectory of –0.06 z-score/year from diagnosis. Pubertal (vs prepubertal) status at diagnosis predicted a lower BMD (-0.51) at baseline. Increased rate of deterioration of BMD trajectory was predicted by pubertal status at diagnosis (-0.16), increased interval cumulative steroid exposure (-0.12) and decreased weight z-scores (0.17). Conclusions LS BMD of pSLE children followed a deteriorating trajectory. Predictors of BMD trajectory were pubertal status at diagnosis, interval cumulative doses of steroids and weight z-scores. Interval cumulative steroid dose is an important target clinicians may modify to ameliorate deteriorating BMD trajectory and future osteoporosis.