What Is Known/What Is New
What Is Known
- Children with Crohn disease are at significant risk for impaired bone mineral density.
- Exclusive enteral nutrition avoids the deleterious effects of corticosteroids on bone development and promotes growth.
- Data on the effects of exclusive enteral nutrition on bone health in pediatric Crohn disease are limited.
What Is New
- Low bone mineral density is common even in mild-moderate pediatric Crohn disease.
- Enteral nutrition has a positive effect on a bone formation biomarker but not on bone mineral density at 24 weeks.
- Children with Crohn disease who achieved clinical remission avoided the decrease in bone mineral density seen in those who did not.
Childhood is a critical time for accrual of bone density, which peaks at 18 to 20 years of age (1). Both the inflammatory burden of Crohn disease (CD) and corticosteroids have a negative effect on bone density (2). Indeed, more than half of children with CD will develop osteopenia (3–5). Treatment goals of pediatric IBD include also optimization of linear growth and bone formation (6,7), and thus, it is essential to utilize therapies that can positively impact these parameters. Exclusive enteral nutrition (EEN) has become the preferred treatment option for induction of remission in children, as it avoids the deleterious effects of corticosteroids and promotes growth (7,8).
EEN is associated with a rapid decrease in the production of pro-inflammatory cytokines, including interleukin-6 (IL-6) (9), which has been shown to decrease bone formation in experimental models (10). EEN has, therefore, been assumed to improve bone outcome in CD but it is unclear to what extent. To date, only a few small studies have been published on this topic, and current available data are insufficient to draw definite conclusions on the effect of nutritional therapy on bone mass (11–14).
As part of a randomized controlled trial (RCT) comparing Crohn disease exclusion diet with EEN in children with mild-moderate CD (15), we performed a planned sub-study aiming to explore the effect of nutritional therapy on bone health in pediatric CD.
Twelve centers (10 in Israel and 2 in Canada) enrolled children 4 to18 years of age with mild-moderately active inflammatory CD (Pediatric CD Activity Index [PCDAI] 10–40 points) diagnosed within the previous 36 months. Patients were excluded if they had isolated colitis with significant rectal involvement, perianal disease, stricturing or penetrating complications or if they had extraintestinal disease. In terms of previous or concomitant therapies, patients could be on stable doses of mesalamine or on immunomodulators commenced at least 8 weeks before enrollment; patients with current or previous biologic treatment or enteral nutrition as well as current steroids were excluded. The current planned sub-study included patients only from the 10 Israeli centers; nearly all of the patients in this cohort had new-onset disease.
Treatment Protocol and Endpoints
Participants were randomized to receive either 6 weeks of EEN followed by 6 weeks of 25% partial enteral nutrition (PEN) with free diet (group 1) or 6 weeks of 50% PEN and 50% exclusion diet followed by 6 weeks of 25% PEN and 75% exclusion diet (group 2). At physicians’ discretion, patients could initiate thiopurines at or after week 3, and methotrexate at or after week 6.
The primary endpoints were serum biomarkers of bone formation and resorption at 12 and 24 weeks, and bone mineral density (BMD) at 24 weeks. Serum biomarkers were determined at weeks 0, 12, and 24. Bone formation was measured by the C-Propeptide of Type I Procollagen (CICP, measured as ng/ml, using the Quidel MicroVue CICP kit) (16) and bone resorption by type I Collagen N-Telopeptide (NTX, measured as bone collagen equivalents/l, using the Alere Osteomark® NTx kit) (17). NTX values exceeding 80 BCE/L (the upper limit of quantification) were considered to have a value of 80 BCE/L for the statistical analysis. Serum samples were drawn at the same time of day at all time-points to avoid intra-subject variability.
BMD was assessed by dual energy X-ray absorptiometry (DXA) scans calculating the z scores of total body less head (TBLH) and, separately, L2-L4 lumbar spine at weeks 0 and 24, adjusted for age and height using the Children's Hospital of Philadelphia online calculator based on the Zemel reference curves (18). Clinical remission was defined as PCDAI <10.
As the RCT was not powered for the secondary endpoint of bone health, we analyzed the 2 study arms together and performed paired analysis of the change in bone parameters over time—before and after the dietary intervention. This was justified by similar effectiveness rate of both treatment arms (week 6 corticosteroid-free remission of 75% for CD exclusion diet with PEN vs 59% for EEN, P = 0.38) (15). Discrete variables were analyzed utilizing Fisher exact test; continuous variables were analyzed with paired Student t test for normally distributed data, with the sign test for paired nonparametric data and the Mann-Whitney U-test for unpaired nonparametric data. For the paired analysis, missing week 12 biomarker values were imputed from week 24 values and missing week 24 biomarkers were imputed from week 12 values. The study was approved by the local ethics committee/institutional review board in each of the participating centers. Missing week 24 clinical remission values were imputed by the last observation carried forward principle. The effect of medical therapy on bone density was explored by comparing the change in bone biomarkers from week 0 to week 24 between patients who received immunomodulator therapy and those who did not, using the Mann-Whitney U-test. Governed by our aim to explore the impact of treatment on bone health, patients who dropped out of the study within the first 3 weeks were excluded from the analysis as this period is unlikely to affect bone status.
The bone sub-study group included 45 of the 78 children enrolled in the original study, who had baseline DXA scan or biomarkers or both. Mean age was 13.7 ± 2.9 years and median disease duration was 1 (0--2) month (Table 1). In order to ensure that disease severity in the bone sub-study group was comparable to the complete cohort, we compared PCDAI in the 2 groups: mean PCDAI in the subset was 26.7 ± 9.7 compared with 27.0 ± 9.2 in the complete cohort; 2-tailed t-test found no significant difference, with a P value of 0.90. At the end of the follow-up period at week 24, 34/45 (76%) of patients in the bone sub-cohort were in clinical remission. Thirty-three (73%) commenced medical therapy, including 16 (36%) thiopurines, 10 (22%) methotrexate, 3 mesalamine (7%), and 4 (9%) infliximab with or without a concomitant thiopurine.
TABLE 1 -
Baseline characteristics of included children
||Entire cohort n = 45
||Exclusion diet with PEN n = 23
||EEN, n = 22
||13.7 ± 2.9
||13.5 ± 3.1
||14.0 ± 2.7
|PCDAI: remission (<10)
| Mild (≥10–30)
| Moderate-severe (>30)
|Disease location: Paris L1
|Disease location: Paris L2
|Disease location: Paris L3
|Disease location: Paris L4a
|Disease location: Paris L4b
Counts (%), medians (interquartile range), and means ± SD are presented as appropriate. EEN = exclusive enteral nutrition; L1 = ileal disease (distal 1/3); L2 = colonic disease; L3 = ileocolonic disease; L4a = upper disease proximal to ligament of Treitz; L4b = upper disease distal to ligament of Treitz and proximal to distal 1/3 of ileum; Paris = Paris classification of pediatric CD; PCDAI = pediatric Crohn disease activity index, a score of <10 is considered as clinical remission; PEN = partial enteral nutrition.
Bone biomarkers were available for 29 children who had at least 1 repeat value at week 12 and/or week 24 (22 had week 12 values and 21 had week 24 values and 13 had both) including 9 that did not have DXA scans. Paired analysis of individual patients showed a significant increase in CICP from baseline (130 [106–189]) to week 12 (223 (143–258); P = 0.016)) and to week 24 (193 [143–252]; P = 0.016) (Fig. 1). NTX remained unchanged from baseline (36 [30–58]) to week 12 (50 [28–66]; P = 0.45) and to week 24 (37 [28–66]; P = 0.45). Several NTX values were above the upper limit of quantification (>80 BCE/L): 1/29 at baseline, 5/27 at week 12, and 2/26 at week 24. Comparison of change from week 0 to week 24 between patients who achieved remission and those who did not found no difference between the groups for either biomarker.
As the nutritional intervention was limited to 12 weeks and most patients initiated medical therapy during the course of the study, we tested whether the improvement in CICP was confounded by the medical therapy received. The change in CICP from week 0 to week 24 (ΔCICP) was compared between patients who received immunomodulator therapy (excluding 2 who additionally received infliximab) and those who received no therapy or mesalamine. Median (interquartile range [IQR] 1–3) ΔCICP in the immunomodulator group was 39 ng/mL (12--79) compared with 8 (−29 to 54) in the no therapy group (P = 0.27). A sensitivity analysis performed without imputing missing values at week 24 (8 imputed values) found a ΔCICP in the immunomodulator group of 39 (12--71) compared with −10.5 (−37 to 28) in the no therapy group (P = 0.051).
DXA scans were available for 36 children, including 27 with TBLH measurements; 26 also had follow-up values, including 22 for TBLH. At baseline, 81% of the inception cohort had an adjusted TBLH z score ≤−1, and 33% had z score ≤−2 (Fig. 2). Similar rates were noted at 24 weeks (86% [P = 0.72] and 36% [P = 1.0], respectively). Similarly, the mean TBLH z scores did not improve from baseline (−1.62 ± 0.87) to week 24 (−1.76 ± 0.75; P = 0.30) (Fig. 3). No patients with abnormal BMD at baseline normalized their BMD at week 24. Of note, mean lumbar BMD z scores actually worsened from −0.08 ± 0.98 at baseline to −0.72 ± 0.74 at week 24; paired P = 0.007). Further subgroup analyses by concomitant therapy (immunomodulator therapy vs no therapy or mesalamine) and treatment arm revealed no differences. These analyses were, however, underpowered because of the small number of patients in each group. Finally, we compared the change in BMD from week 0 to week 24 (ΔBMD) between patients who achieved remission and those who did not, and found that patients who achieved remission had a mean TBLH ΔBMD of 0.06 ± 0.51 (n = 15) versus −0.64 ± 0.55 (P = 0.04) for patients who did not achieve remission (n = 6). The difference was not significant for lumbar ΔBMD (−0.36 ± 0.91 [n = 19] vs −0.73 ± 0.71 [n = 7], P = 0.33)
In this multicenter prospective study, we found that one-third of children with mild-moderate CD had BMD z score of less than −2 at disease onset whereas three quarters had less than −1. CICP, a marker of bone formation, increased significantly at 12 weeks and remained elevated compared with baseline at 24 weeks after nutritional intervention followed by various maintenance medical therapies. This did not translate into improved BMD on DXA scans, however. NTX, a marker of bone resorption, showed no change at 12 and 24 weeks.
The lack of improvement in DXA scan is consistent with adult studies that generally reported minor improvement if at all of bone density with anti-tumor necrosis factor (anti-TNF) therapy. (19,20). In contrast, bone biomarkers have shown improvement following initiation of anti-TNF treatment both in adults (21–24) and in children (25–27). Two pediatric studies showed improvement in BMD after commencing on infliximab therapy (26,28), whereas 1 smaller study showed none (27).
Four studies explored the effect of enteral nutrition on bone health in CD, all in children and all smaller than the current study. In a retrospective case series, Soo et al (11) found no significant change in lumbar DXA scores in 16 children with CD on EEN. Whitten et al (12) prospectively studied 23 children with CD on EEN and found improvement in markers of bone formation and bone resorption at 8 weeks but did not measure BMD. Werkstetter et al (13) prospectively studied 10 children with CD who received 8 weeks of EEN along with azathioprine maintenance; they found a rapid increase in markers of bone formation and bone resorption with no further improvement later on, along with improved BMD at week 12 as measured by peripheral quantitative computer tomography (pQCT). Recently, Strisciuglio et al (14) prospectively studied 25 children receiving EEN as induction therapy for CD and found a significant improvement in BMD at week 52; 8 of these received azathioprine and none received biologics. Only children who achieved clinical remission (18/25) were, however, included in the analysis.
The lack of improvement in BMD along with biochemical indication of increased bone formation may suggest that the biochemical change might be a precursor to increased BMD, which is a much slower process that would be expected to occur later than 24 weeks. The studies that found an improvement in BMD all used 12 months or later for this endpoint (13,19,20,26,28). We selected the earlier time point as later assessment would have been biased by interventions commenced following the 8-week dietary intervention. Only 2 children were commenced on biologics during this time frame. As immunomodulators gain full effectiveness in many patients only after 3 to 4 months of treatment and these were commenced after the 2-month dietary intervention period, we did not anticipate that a significant effect would have been apparent at a 6-month visit. In order to explore the potential effect of immunomodulators, we performed a sensitivity analysis that found no difference in bone health between those receiving immunomodulators and those on no therapy or mesalamine. We did, however, find that the change over time in TBLH BMD differed between children who achieved remission and those who did not, as those who achieved remission had stable values over 24 weeks whereas those who did not had a decrease.
Regarding bone resorption, our negative findings appear to be consistent with previous pediatric studies that generally failed to detect improvement in bone resorption biomarkers with therapy. Only 1 study found an improvement (12), whereas the others found bone resorption biomarkers to be either unchanged (27) or worsened (13,25,26). In addition, the NTX biomarker analysis was hampered by the several values truncated at the upper limit of quantification. As all week 12 and 24 upper limit values, however, had measurable baseline values <80, the results of the nonparametric sign test we utilized would not have been different had the true value been used.
Limitations of our study include the fact that the original study was statistically powered for the clinical endpoint of tolerance to the CD exclusion diet, and thus the bone analysis may have been underpowered. Furthermore, a fairly high number of patients from the original study was not represented in various bone analyses because of nonperformance of DXA scans or biomarker tests. As a result, our ability to perform reliable subset analyses was limited. It is, however, unlikely that significant selection bias occurred, as the selection was not of a systematic nature.
Strengths of our study include the prospective design and data collection. In particular, prospective measurement of bone metabolism biomarkers enabled properly timed measurement, as the biomarker levels fluctuate throughout the day because of circadian variation. An additional strength is the focus on a well-defined patient population—new-onset pediatric CD.
In conclusion, we found that osteopenia is a frequent silent complication of new-onset pediatric CD, even in the mild-moderate group. Nutritional treatment improved CICP, a responsive and sensitive marker of bone formation, but not BMD, implying that bone improvement is a challenging and a slow process. Children who achieved clinical remission did, however, avoid the decrease in BMD seen in those who did not. As childhood is the time in which bone is accrued, timely and appropriate therapy towards endoscopic healing and steroid-sparing may potentially ameliorate deficits that could later become irreversible.
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