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Vitamin B-12 is absorbed from the terminal ileum, which is a commonly affected segment of gut in Crohn’s disease. Its absorption may be compromised in these children secondary to inflammatory lesions, ileal bacterial overgrowth, or mucosal damage caused by reflux of bacteria and surgical resection.1 Of these, surgical resection of large segments of terminal ileum remains the most important cause of B-12 malabsorption in such patients. Prolonged depletion leads to megaloblastic anaemia and ultimately neuropathy and myelopathy. Therefore, diagnosis and treatment of vitamin B-12 malabsorption in patients with Crohn’s disease and small bowel/ileal resection is of great importance.
There is a paucity of published paediatric data on vitamin B-12 absorption after resection of the ileum in childhood. Valman and Roberts observed impaired absorption of vitamin B-12 in 7 of 10 infants and children who had resection of >45 cm of ileum.2 Absorption was however normal in 2 of 10 children who had 15 cm or more terminal ileum remaining. Impaired B-12 absorption after significant (>60–180 cm) ileal resection may be permanent; however in children, adaptation of the remaining small bowel may result in restoration of its absorption several years after ileal resection.3
Our anecdotal experience and communication with other paediatric gastroenterology centres in the UK suggested that there is no common management strategy regarding B-12 supplementation after ileal resection. We, therefore, retrospectively examined in our own unit the impact of small bowel surgery on vitamin B-12 levels in 18 children with ileal resection secondary to Crohn’s disease over a period of 10 years. All patients except one had normal or low mean corpuscular volume and mean corpuscular concentration throughout their follow up before and after surgery. Median age at surgery was 15 years. Nine children had <30 cm of ileal resection and eight children 30–50 cm of terminal/distal ileum resected. Only one patient needed >70 cm of ileal resection. None of these children were observed to have low vitamin B-12 levels before or after small bowel surgery (for 1–8 years after surgery).
Our review of this small case series further highlights the significance of as yet unanswered question of vitamin B-12 supplementation in this group of children. As clinical and haematological B-12 deficiency may take several years to develop, serum B-12 levels alone may not be sufficient to decide about the need for its supplementation and regular formal B-12 absorption tests may be required. We feel that a large multicentre prospective cohort study is required to evaluate the need for regular monitoring of vitamin B-12 levels, its absorption tests, and the need for supplementation in children with Crohn’s disease needing small bowel surgery.