may cause iron-deficiency anemia Nausea and vomiting particularly with stricturing disease/obstruction Urgency and tenesmus with rectal/colonic involvement Weight loss and malnutrition due to malabsorption, food avoidance, elevated metabolic demand Fever with active inflammation, abscess, or fistula Perianal disease fissures, fistulae, skin tags, abscesses Extraintestinal Manifestations Arthropathy peripheral or axial (enteropathic arthritis, M07.6x) Dermatologic: Erythema nodosum (L52), pyoderma gangrenosum, psoriasis (L40.5) Ocular: Uveitis/iritis (H20.01), episcleritis, scleritis Hepatobiliary: Primary sclerosing cholangitis (K73.2), fatty liver, cholelithiasis Metabolic: Osteopenia/osteoporosis (from steroid use and malabsorption), nephrolithiasis Hematologic: Anemia (iron deficiency, B12/folate deficiency, anemia of chronic disease) When a patient with Crohns disease is admitted with significant weight loss, malnutrition, or protein-calorie deficiency , query the provider to specify the degree of malnutrition (mild, moderate, severe protein-calorie malnutrition)

None of these pathways directly substitute for another, which is part of why researchers interested in a fuller picture of metabolic regulation may look at all three within the same body of literature not to combine effects, but to understand how separate systems might interact at a mechanistic level
Fatigue is one of the most common symptoms of B12 deficiency, often described as exhaustion that doesnt improve with sleep
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