Ulcerative Colitis
The most likely diagnosis is ulcerative colitis (Option C). This 23-year-old woman presents with a four-month history of diarrhea with mucus, anemia, and abdominal pain relieved by defecation—a constellation that strongly indicates chronic inflammatory bowel disease rather than a functional disorder, despite the normal ESR 1, 2.
Why Ulcerative Colitis is the Correct Diagnosis
The presence of anemia is an absolute alarm feature that excludes irritable bowel syndrome and mandates investigation for organic disease. 3, 1 The combination of chronic diarrhea with mucus passage, anemia, and pain relieved by defecation is characteristic of ulcerative colitis in young adults 1, 2.
Chronic diarrhea lasting four months with mucus indicates mucosal pathology, not functional disease. 1, 2 Ulcerative colitis classically presents with bloody diarrhea (often with mucus), rectal urgency, and abdominal pain that improves after defecation 1, 2.
Anemia confirms systemic disease impact and rules out non-organic causes, even when inflammatory markers are normal. 1 The normal ESR should not provide false reassurance—inflammatory markers have poor sensitivity, with 15-20% false-negative rates in active inflammatory bowel disease 1.
The age of onset (23 years) falls within the peak incidence for ulcerative colitis, which occurs in the second or third decade of life. 2, 4
Why Other Options Are Incorrect
Irritable Bowel Syndrome (Option A) is Excluded
IBS diagnosis requires the absence of alarm features—anemia is an absolute contraindication to diagnosing IBS. 1, 5 Diagnosing IBS in the presence of anemia is a fundamental error that can delay serious diagnoses 5.
IBS patients have normal inflammatory markers AND normal hemoglobin—this patient has anemia. 1 The presence of any alarm feature (fever, weight loss, blood in stools, anemia) mandates pursuit of an IBD workup rather than IBS diagnosis 1.
Colon Cancer (Option B) is Extremely Unlikely
Colon cancer is exceedingly rare in patients under 30 years of age unless there is a strong family history of early-onset colorectal cancer. 1 A relative diagnosed at age 60 represents typical-onset disease, not a hereditary syndrome 1.
The family history described (relative at age 60) increases risk only 2.5-fold, not the 9.2-fold risk seen with first-degree relatives diagnosed before age 50. 3, 5 This level of family history does not make cancer the primary consideration in a 23-year-old 3.
While colonoscopy is ultimately required to exclude malignancy, the clinical picture overwhelmingly favors inflammatory bowel disease. 1, 5
Gastroenteritis (Option D) is Ruled Out by Chronicity
Infectious gastroenteritis typically resolves within days to weeks—a four-month duration makes chronic inflammatory disease far more likely. 1, 6 Persistent symptoms of this duration indicate chronic idiopathic inflammatory bowel disease rather than acute infection 1, 6.
While infectious causes must be excluded (particularly Clostridium difficile), the prolonged course strongly suggests ulcerative colitis. 3, 1
Essential Next Steps in Management
Immediate workup must include complete blood count to quantify anemia, stool studies for infectious pathogens including C. difficile, and colonoscopy with biopsies within 30 days. 3, 1, 5
Colonoscopy with targeted biopsies from both inflamed and normal-appearing segments is the definitive diagnostic method. 1, 2 Typical endoscopic findings include continuous inflammation beginning in the rectum, loss of vascular pattern, mucosal granularity, friability, and ulceration 1, 2.
Stool testing for pathogens must be performed before confirming ulcerative colitis, as infectious colitis can mimic IBD. 3, 1 However, the chronicity makes infection unlikely as the primary diagnosis 1.
Fecal calprotectin, if available, would show values >200-250 μg/g, strongly supporting IBD and mandating endoscopic evaluation. 1 Values <50 μg/g would exclude IBD and point toward functional disorders 1.
Critical Clinical Pitfall
Never diagnose IBS in the presence of anemia—this is the most dangerous error in this clinical scenario. 1, 5 The normal ESR does not exclude inflammatory bowel disease, as 15-20% of patients with active Crohn's disease have normal CRP, and similar rates apply to ulcerative colitis 3, 1. The combination of alarm features (anemia, chronic mucoid diarrhea) mandates endoscopic evaluation regardless of normal inflammatory markers 1, 5.