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smass index (FMI) (fat mass(kg)/height(m)2) and appendicular skeletal muscle index (ASMI)(appendicular lean mass(kg)/height(m)2). Relationships amongst variables were examinedwith correlation coefficients. Results To date, we have data on 71 IBD patients, 41 (58%)males, 54 (76%) with Crohn's Disease, 15 (21%) ulcerative colitis, and 2 (3%) IBD unspeci-fied. The mean age was 34.3, median 32.8 (range 19 to 50) years. The mean BMI amongstthe cohort was 27.1 kg/m2, median 25.3, males 26.5 and females 28. BMI was found tobe a good predictor of fat mass, with a close correlation between BMI and FMI in bothmales and females (r2=0.91, r2=0.96 respectively) (Fig 1). However, by comparison, BMIdid not correlate as well with ASMI in either males or females (r2=0.69, r2=0.67 respectively)(Fig 2). Conclusion In this cohort of mixed IBD patients, BMI was normal. BMI is a goodpredictor of fat mass but a poorer predictor of lean mass amongst adult IBD patients.Interpretation of nutritional status on the basis of BMI should be viewed with caution giventhe propensity to miss deficits in lean mass in this cohort predisposed to malnutrition. Giventhe known propensity for fat gain with steroid therapy, there is a risk that deficits in leanmass will be missed unless specifically sought.

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Cumulative Length of Bowel Resection in a Population-Based Cohort ofCrohn's DiseaseLaurent Peyrin-Biroulet, William S. Harmsen, William J. Tremaine, Alan R. Zinsmeister,William Sandborn, Edward V. Loftus

Background: A referral-based study suggested that the length of post-operative recurrentCrohn's was similar to the length of pre-surgical Crohn's disease (Gut 1995;36:715-717).Although several population-based studies of Crohn's disease have described the cumulativeprobability of surgery, there are limited data on the cumulative extent of bowel resectionin these patients. Methods: Using the resources of the Rochester Epidemiology Project, wehave previously identified a cohort of 310 incident cases of Crohn's disease among OlmstedCounty, Minnesota residents diagnosed between 1970 and 2004. One hundred fifty-twopatients underwent at least one abdominal surgery, including 147 patients who underwentat least one bowel resection (Am J Gastroenterol 2012;107:1693-1701). Operative reportsand corresponding pathology reports were abstracted for bowel resection length—these datawere available for all but 6 patients. Median bowel resection lengths (with interquartilerange, IQR) were calculated per resection, cumulatively, and as a rate per year of follow-up. Repeated measures analysis of covariance was used to compare successive resectionlengths. Results: Median follow-up per patient was 13.6 years (range, 0.2-39). Among the141 patients with resection data available, a total of 211 resections were performed (100with 1, 24 with 2, 9 with 3, 6 with 4, 1 with 5, and 1 patient with 7 resections). Medianlengths of small bowel (SB), colon and total bowel resected at any, first, second, and thirdresections and cumulatively are shown in Table 1. The length of the first resection wassignificantly greater than that of the second (p=0.002), without significant differences betweensecond and third or subsequent. The median (IQR) "rate" of bowel resected in this cohortwas 2.4 cm SB per year (1.2-4.8), 1.5 cm colon yearly (0.5-3.6), and 4.2 cm total bowelannually (2.8-7.7). Conclusions: In this population-based cohort of Crohn's disease, themedian length of bowel resected was highest for the first resection (52 cm). The median

S-634AGA Abstracts

cumulative length of bowel resected among the 141 patients who underwent at least oneresection was 64 cm. The length of subsequent resections was significantly lower than thatof the first resection. The median rate of bowel loss due to resection in the subset requiringat least one resection was 4.2 cm annually, highlighting the fact that Crohn's disease canbe a progressive, destructive illness in a subset of patients with the condition.Median Bowel Resection Lengths in a Population-Based Cohort of Crohn's Disease

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Predictors of Long-Term Outcomes of Perianal Fistulizing Crohn's DiseaseBelinda Tchoundjeu, Tanguy Rohou, Guillaume Bouguen, David Cuen, TimotheeWallenhorst, Isabelle Berkelmans, Yves Gandon, Jean-François Bretagne, LaurentSiproudhis

BACKGROUND The treatment of perianal fistulizing Crohn's disease remains a challengein clinical practice, requiring a combined medical and surgical approach which is ofteninsufficient. The purpose of this study was to identify clinical and imaging based predictorsof the long-term outcome of PCD. METHODS All clinical (including Montreal classification,Harvey Bradshaw, PDAI, UFS) and radiographic (3T MRI) data of Crohn's disease at thetime of management of PCD were recorded in a prospective database. Survival analysis wasused to look for predictors of clinical and anatomical remission of the PCD. RESULTS Theanalysis focused on the clinical outcomes of 122 events in 70 patients with PCD (H/F: 26/44), with a median age of 32 years, and complex fistula in 55 patients. Comparing MRIand clinical assessment of PCD, more than 90% of clinical fistulas (111/122) were identifiedusing MRI. However the concordance of anatomical description between physical examina-tion and imaging was fair: similar for just over half of PCD 71/122 (58.2%). After a medianfollow-up of 33 months (range 17-55), the cumulative probabilities of remission of PCDwere 31% and 43%, at 24 and 36 months respectively. Of note, univariate analysis founda Van Assche score. 15 was associated with a long-term non-healing fistula. Independentpredictors of poor outcomes of PCD were tobacco use (HR 8.9 [2.8 to 40.8], p ,0.0001),female gender (HR = 7.1 [2.8 to 18.6], p ,0.0001), the presence of perianal lesions at thetime of initial Crohn's disease diagnosis (HR = 2.9 [1.3 to 7.4], p ,0.007), the B1 phenotype,the lateral extension of PCD of more than 30% of the anorectal circumference (HR =17.8[5.7 to 58.3], p ,0.0001) and inflammatory disease of the rectal wall on MRI (HR = 6.5[2.5 to 25.2], p ,0.0001). CONCLUSION Some MRI or clinical features are associated witha poor outcome of PCD. Physicians should consider these predictors when choosing therapiesfor PCD.

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Natural History of Elderly Onset Inflammatory Bowel Disease - Sydney IBDCohort (1942-2012)Viraj C. Kariyawasam, Tony D. Huang, Paul C. Lunney, Kate Middleton, Rosy R. Wang,Christian P. Selinger, Peter Katelaris, Jane M. Andrews, Rupert W. Leong

Background: The incidence of inflammatory bowel disease (IBD) is increasing in the elderly.They have unique management related issues and hence require individualised therapy.However, little data is available on the natural history of disease and the impact of immunomo-dulation (IM) (Azathioprine, Mercaptopurine and Methotrexate) to guide such decisions.Aim: The aim of this study was to describe differences in disease characteristics and treatmentmodalities in an elderly onset IBD cohort and compare this to younger onset (YO) IBDcohort. Method: "Sydney IBD cohort" database was interrogated. Patents diagnosed over theage of 60 and 16-40 were selected. Patient demographics, disease characteristics as perMontreal classification, medication and surgical history were reviewed. Kaplan Meier, logrank and Cox proportional hazard regression model statistics were used. Results: A total of284 (12%) had IBD diagnosed after the age of 60, with 119(42%) had Crohn's disease (CD),144(51%) ulcerative colitis (UC) and 21(7%)IBD-unclassified (IBD-U). Elderly onset CDpatients had a median follow-up of 7 years (IQR 2-13) and 1,012 patient years of follow-up. The median age of diagnosis was 68 years. The cumulative probability (CP) of introducingIM, having intestinal resection and disease progression was significantly lower compared toYO patients (Table 1). B1 as opposed to B2/B3 was the only significant predictor of decreasedneed of surgery (P=0.003, HR 0.03, 95% Confidence interval 0.004-0.314). Elderly UCpatients had a median follow up of 8 years (IQR 3-15) and 1,374 patient years of follow-up. The median age of diagnosis was 67 years. They had significantly lower CP of beinginitiated on IM as opposed to YO but without a significant difference in the CP of colectomyover time (Table 2). Early introduction of IM predicted decreased CP of having surgicalresection (P=0.014) in elderly. Conclusions: CD diagnosed in elderly is less likely to progressand require surgery despite significantly lower exposure to IM. UC patients' have similarcolectomy rates as YO despite having lower use of IM. Therefore careful patient selectionis needed prior to initiating IM in this group of patents, as risk/benefit of long-term immuno-suppression may not be as acceptable as in YO patients.Table 1. Comparison between elderly onset and younger onset Crohn's disease patients