What is the likely diagnosis for a 25-year-old patient with abdominal pain, bloody diarrhea, and weight loss, a positive guaiac (fecal occult blood test) stool test, and a family history of similar complaints?

Diagnosis: Ulcerative Colitis

The most likely diagnosis is ulcerative colitis (Option A), given the constellation of 3 months of bloody diarrhea, abdominal pain, weight loss, positive fecal occult blood test, and critically, a strong family history of similar symptoms in both mother and brother. 1

Clinical Reasoning

Classic Presentation Matches UC

• Bloody diarrhea is the hallmark symptom of ulcerative colitis and strongly indicates disease activity 2, 3
• The triad of abdominal pain, bloody diarrhea, and weight loss is characteristic of inflammatory bowel disease, particularly UC in this age group 1, 3
• The 3-month duration qualifies as chronic symptoms (>4 weeks), consistent with IBD rather than infectious causes 1
• Weight loss correlates with more severe disease activity 2

Family History is Decisive

• The presence of similar symptoms in both mother and brother strongly suggests a genetic inflammatory bowel disease rather than familial adenomatous polyposis (FAP) 1
• UC has significant genetic predisposition, and family history is a key risk factor 1, 3
• FAP typically presents with polyps discovered incidentally or through screening, not with bloody diarrhea and systemic symptoms like weight loss 1

Why Not the Other Options

Familial Adenomatous Polyposis (Option B) is unlikely because:

• FAP patients typically present with polyp-related complications or are identified through family screening, not with the acute inflammatory symptoms described 1
• While FAP can cause diarrhea, the combination of bloody diarrhea, abdominal pain, and weight loss with positive family history points more toward inflammatory bowel disease 1
• The age of 25 and symptomatic presentation with inflammation is more consistent with UC than FAP 1

Diverticulosis (Option C) is highly unlikely because:

• Diverticulosis is extremely rare in 25-year-old patients; it typically affects individuals over 60 years 1
• The family clustering of identical symptoms argues against diverticulosis 1
• While segmental colitis associated with diverticulosis exists, it occurs in elderly patients with pre-existing diverticular disease 1

Diagnostic Approach

Immediate Next Steps

• Perform colonoscopy with biopsies to confirm diagnosis - this is the gold standard for UC diagnosis 1, 2
• Look for continuous mucosal inflammation extending from rectum proximally, with loss of vascular pattern, granularity, friability, and ulceration 1, 3
• Obtain stool cultures to exclude infectious causes including C. difficile 1

Laboratory Evaluation

• Complete blood count (assess for anemia from chronic bleeding) 1
• ESR and CRP (elevated in active inflammation) 1, 2
• Serum albumin (hypoalbuminemia indicates severe disease) 1, 2
• Fecal calprotectin (levels >250 μg/g strongly correlate with active inflammation) 2

Histologic Confirmation

• Histopathology should show decreased crypt density, crypt architectural distortion, irregular mucosal surface, and heavy diffuse transmucosal inflammation without granulomas 3
• Absence of granulomas helps distinguish UC from Crohn's disease 1

Critical Pitfalls to Avoid

• Do not delay endoscopic evaluation - colonoscopy with biopsy is essential for definitive diagnosis and cannot be replaced by clinical assessment alone 1
• Always exclude infectious causes before diagnosing IBD, particularly C. difficile, even without recent antibiotic use 1
• Consider Crohn's disease in the differential, though the family history pattern and bloody diarrhea favor UC 1
• In young patients with bloody diarrhea and family history, IBD should be the primary consideration over other causes 1