Altered bone metabolism in inflammatory bowel disease.

UNLABELLED: A reduced bone mineral density has been reported in inflammatory bowel disease (IBD).

OBJECTIVE

To assess the mechanisms of bone disease in IBD.

METHODS

We studied in 90 patients (61 with Crohn's disease, 22 with ulcerative colitis, 7 with indeterminate colitis) biochemical markers of bone metabolism in serum and bone mineral density by peripheral quantitative computed tomography at the forearm.

RESULTS

Forty-five percent of the patients had a reduced bone density (Z score < -1). Serum calcium was normal in most patients, vitamin D deficiency was documented in 17%. Osteocalcin, a serum marker of bone formation, was decreased in 26% (1.2 +/- 0.1 ng/ml), whereas the carboxyterminal cross-linked telopeptide of type I collagen (ICTP), a recently described serum parameter of bone breakdown, was stimulated in 38% (10.4 +/- 2.3 microg/L). Of 33 patients with increased ICTP levels, 19 showed a decreased bone density (Z score < -1), and 2 of them never received steroids. An active status of the underlying disease in most patients with increased ICTP levels suggests a direct effect of the underlying IBD. In the whole series of patients with a history of active disease (n = 34), 47% had signs of an increased bone degradation (ICTP > 5 microg/L; mean, 12.9 +/- 4.7 microg/L). Data derived from a retrospective survey of 245 patients with IBD suggest that the prevalence of bone fractures in IBD is unexpectedly high, particularly in patients with a long duration of disease, frequent active phases, and high cumulative doses of corticosteroid intake.

CONCLUSIONS

Several mechanisms may be involved in IBD-associated bone disease: (1) a high inflammatory activity directly induces bone degradation via yet unknown pathways, (2) treatment with corticosteroids may exert catabolic effects on the bone, or (3) malabsorption and vitamin D deficiency may activate bone turnover.