Bone metabolism and inflammatory bowel disease

Abstract

A serious and silent complication of inflammatory bowel disease (IBD) is the development of osteoporosis [1-3]. Osteoporosis is a systemic skeletal disease characterized by low bone mass, microarchitectural deterioration of bone tissue and increased bone fragility and susceptibility to fracture [4]. Milder bone loss or osteopenia is defined as a bone mineral density (BMD) that is 1.0-2.49 standard deviations below a control population, and osteoporosis as BMD that is less than 2.5 standard deviations below a control population [5] (Table 1). Estimates of osteopenia in IBD range from 31% to 59% [6, 7] and osteoporosis from 5% to 41% [1, 8- 11]. Bone loss is more prevalent in patients with Crohn's disease (CD) than those with ulcerative colitis (UC), and this may be related to the fact that childhood onset of CD does not allow children to reach peak bone mass [1]. In a prospective series of patients with IBD the rate of bone loss over a 19- month period was -3.1 for CD, -6.4 for UC (includes patients on steroids) and +2.0 for UC after an ileoanal anastomosis [12]. The reasons for development of osteopenia and osteoporosis are multiple and include steroid-induced bone loss [12-15], malabsorption of nutrients [16, 17], vitamin D deficiency [18], smoking [19], and inflammatory cytokines [9, 20] (Table 2). Based on the high prevalence of osteopenia and osteoporosis in patients with IBD, a baseline evaluation of BMD is warranted, especially in patients with CD [21]. The diagnosis of osteopenia and osteoporosis is most often made by dual-energy X-ray absorptiometry (DEXA) of the lumbar spine, proximal femur, and forearm, but can be made using other techniques such as calcaneal ultrasound or quantitative computed tomography [22, 23]. In addition to DEXA scanning for BMD, other serum and urinary markers are available for assessment of bone turnover. In patients with IBD, measurement of urinary N-telopeptide crosslinked of Type 1 collagen, a marker of bone resorption, was the best predictor of spinal bone loss over a 2-year follow-up period compared with other markers, including bone alkaline phosphatase, osteocalcin, parathyroid hormone (PTH) and vitamin D levels [10, 24, 25]. (Table presented). © 2005 Springer Science+Business Media, Inc.