Altered bone metabolism in inflammatory bowel disease: there is a difference between Crohn's disease and ulcerative colitis.

OBJECTIVES: The aims of this study were to assess bone metabolism in inflammatory bowel disease (IBD) patients and to evaluate potential differences between Crohn's disease (CD) and ulcerative colitis (UC) with respect to the mechanisms underlying bone loss in this group of diseases.

DESIGN AND SETTING: This was a cross-sectional study which started in 1992. Patients were randomly selected for invitation to participate and were examined during the years 1992-95 in one research clinic in Milan.

SUBJECTS AND METHODS: Fifty-one patients suffering from CD (30 women and 21 men, mean age 38.7 +/- 13.2 years) and 40 with UC (15 women and 25 men, mean age 34.4. +/- 12.5 years) entered the study. Thirty healthy subjects were selected as sex- and age-matched controls (C). Spine and femoral neck bone mineral density (expressed as T score), calciotropic hormones (parathyroid hormone, PTH; 25-hydroxycholecalciferol, 25(OH)D3; 1,25-hydroxycholecalciferol, 1, 25(OH)D3) and biochemical markers of bone turnover (ostecalcin, OC; total alkaline phosphatase, ALP; type I collagen C-terminal telopeptide, ICTP) were evaluated.

RESULTS: Spine and femur T scores were similar in the two groups (spine: CD = -1.49 +/- 1.46; UC = -1. 67 +/- 1.13; femur: CD = -1.80 +/- 1.36; UC = -1.60 +/- 1.03). Based upon the WHO guidelines, only 8% of CD patients and 15% of UC patients had a normal bone mineral density (BMD), 55% (CD) and 67% (UC) were osteopenic, and 37% (CD) and 18% (UC) were osteoporotic. The distribution amongst the three different diagnostic groups was not significantly different between CD and UC groups (P = 0.11). PTH and 25(OH)D3 concentrations were not significantly different between CD and UC patients and controls, whilst 1,25(OH)D3 concentrations were significantly lower in both CD and UC patients compared with controls (P < 0.05). Bone turnover was increased in UC but not in CD patients, as shown by significantly increased concentrations in UC patients of both OC (CD = 7.77 +/- 5.06, UC = 10.03 +/- 6.24, C = 6. 58 +/- 2.87, P < 0.05 vs. C) and ICTP (CD = 5.74 +/- 3.94, UC = 10.2 +/- 8.47, C = 3.48 +/- 0.95, P < 0.05 vs. CD and C). In a stepwise regression that included age, sex, disease duration and cumulative prednisolone dose as independent variables, the femur T score was significantly inversely related to disease duration (r2 = 0.125, F = 6.06) in CD patients. In UC patients, the spine T score was inversely related to age (r2 = 0.107, F = 5.49) and significantly related to sex (more negative in males: r2 = 0.3, F = 16.1); the femur T score was significantly related to sex (more negative in males) and inversely related to the cumulative prednisolone dose (r2 = 0.283, F = 7.3).

CONCLUSIONS: These data show that IBD patients have a diffuse osteopenia, the degree of which is not different in CD and UC; however, bone turnover is significantly higher in UC. Finally, osteopenia is related to disease duration in CD, whilst it is related to the male sex and glucocorticoid treatment in UC.