BONE DISEASE IN NEWLY DIAGNOSED LUPUS NEPHRITIS PATIENTS

Abstract

Introduction and Aims: Bone disease is an important and preventable condition related to systemic lupus erythematosus (SLE). The role of glucocorticoid therapy as the major event in bone loss has been questioned by recent studies. However, the methodology of most of these studies included only evaluation of bone mineral density by X-ray absorptiometry. The aim of this study was to evaluate bone disease using histomorphometric parameters in newly diagnosed SLE patients. Methods: We included pre-menopausal female patients with =2 months of diagnosed SLE and Lupus Nephritis (LN) according to the American College of Rheumatology classification criteria. Exclusion criteria were: estimated GFR (MDRD) < 30 ml/min/1,73m2 and previous use of drugs that affect bone metabolism (as calcium supplements, anticonvulsants and anticoagulants). Patients were submitted to bone biopsy and histomorphometry analysis was performed according to the American Society for Bone and Mineral Research. The 8 patients included from 2011 January to December were compared to 16 gender and age-matched controls from a Brazilian bone database of healthy individuals (Dos Reis et al. Bone 1998; 23: S476). Results: Patients presented a mean age of 30.5±9.7 years, with a BMI of 23.1±3.0 Kg/m2. They were on glucocorticoid treatment for 35.3±11.5 days, with a cumulative prednisone dose of 5614.4±2039.8 mg. Seven patients (87.5%) presented focal or diffuse proliferative LN and one patient presented membranous LN. Mean 24h proteinuria was 6.0±.1.9 g, with a serum albumin of 2.0±0.7 g/dL and an estimated GFR of 65.1±34.5 ml/min/1.73m2. All patients presented vitamin D deficiency (serum 25-hydroxyvitamin D = 8.8±2.7 ng/ml, range 4-12), probably contributing to an increased iPTH levels (79.4±59.5 pg/ml). Histomorphometric parameters of patients and controls are shown in table 1. We observed that SLE patients presented lower OV/BV and O.Th, suggesting a reduced bone formation. These patients also presented higher ES/BS and Oc.S/BS, revealing an increased bone resorption. Results are expressed as: mean±std or median (25-75 IQR). BV/TV= trabecular volume; Tb.Th= trabecular thickness; Tb.Sp= trabecular separation; Tb.N= trabecular number; OS/BS= osteoid surface; Ob.S/BS= osteoblast surface; OV/BV= osteoid volume; O.Th= osteoid thickness; ES/BS= eroded surface; Oc.S/BS= osteoclast surface. Conclusions: Newly diagnosed LN patients presented a reduced bone formation associated with an increase in resorption parameters. We believe these findings could not be attributed to glucocorticoid use and might actually be related to the active inflammation involved in LN physiopathology.