In a 25-year-old man with weight loss, abdominal pain, bloody stools, a positive fecal occult blood test (guaiac), and a family history of similar gastrointestinal symptoms, what is the most likely diagnosis: Peutz–Jeghers syndrome, familial adenomatous polyposis, ulcerative colitis, or Crohn disease?

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Most Likely Diagnosis: Crohn Disease

In a 25-year-old man presenting with weight loss, abdominal pain, bloody stools, positive fecal occult blood test, and a strong family history of similar gastrointestinal symptoms, Crohn disease is the most likely diagnosis.

Clinical Reasoning

Key Discriminating Features

The clinical presentation strongly favors Crohn disease based on several critical factors:

  • Age and symptom triad: Crohn disease characteristically presents in young adults (second or third decade) with the classic triad of abdominal pain, unexplained weight loss, and bloody diarrhea 1.

  • Weight loss prominence: Weight loss is more pronounced in Crohn disease compared to ulcerative colitis because small-bowel involvement leads to malabsorption of nutrients 1. This patient's significant weight loss is a key distinguishing feature.

  • Abdominal pain pattern: The abdominal pain in Crohn disease is a cardinal symptom reflecting active inflammation, stricturing, or fistulizing disease, and characteristically may not be relieved by defecation 1. This differs from ulcerative colitis where pain is often relieved by bowel movements.

  • Family history significance: First-degree relatives with inflammatory bowel disease increase an individual's risk of developing IBD by approximately 2-3 fold 1. The presence of similar symptoms in the mother and siblings strongly suggests an inherited inflammatory bowel disease rather than a polyposis syndrome.

Why Not the Other Options?

Familial Adenomatous Polyposis (FAP):

  • FAP presents with hundreds of adenomatous polyps throughout the colon and rectum, typically identified during surveillance sigmoidoscopy at ages 12-15 years 1.
  • The disease carries an almost 100% lifetime risk of colorectal cancer, necessitating prophylactic colectomy between ages 20-25 years 1.
  • This patient's presentation lacks the characteristic endoscopic finding of numerous polyps, and the symptom complex of weight loss and abdominal pain is not typical for FAP.

Peutz-Jeghers Syndrome:

  • Over 90% of individuals with Peutz-Jeghers syndrome exhibit characteristic mucocutaneous melanin pigmentation on the lips and oral mucosa 1, which is not mentioned in this case.
  • The syndrome is extremely rare, with an incidence of 1:50,000 to 1:200,000 1, making it a much less likely differential diagnosis.
  • Peutz-Jeghers is associated with hamartomatous polyps rather than the inflammatory changes expected in this patient 2, 3.

Ulcerative Colitis:

  • While ulcerative colitis does present with bloody diarrhea and can occur in young adults 4, 5, several features make it less likely:
    • The prominent weight loss is more characteristic of Crohn disease due to small bowel involvement and malabsorption 1.
    • Ulcerative colitis classically presents with bloody diarrhea with or without mucus, rectal urgency, and tenesmus, with abdominal pain often relieved by defecation 4—a different pain pattern than suggested here.
    • The family history pattern and the combination of significant weight loss with abdominal pain favor Crohn disease.

Diagnostic Confirmation

  • The positive fecal occult blood test confirms gastrointestinal bleeding but does not differentiate between Crohn disease, ulcerative colitis, or other causes 1.

  • Ileocolonoscopy with biopsy is essential to make a definitive diagnosis, looking for:

    • Transmural inflammation characteristic of Crohn disease 1
    • Skip lesions (discontinuous inflammation) rather than the continuous inflammation seen in ulcerative colitis 4
    • Granulomas on histology, which are pathognomonic for Crohn disease when present 4

Common Pitfalls to Avoid

  • Do not assume ulcerative colitis simply because of bloody stools—the prominent weight loss and abdominal pain pattern favor Crohn disease 1.

  • Do not overlook the family history: A 2-3 fold increased risk with first-degree relatives having IBD makes inflammatory bowel disease far more likely than rare polyposis syndromes 1.

  • Do not delay colonoscopy: Any positive stool test for blood requires follow-up with colonoscopy to identify the source of bleeding 6.

  • Remember that symptoms may not correlate with disease severity: In inflammatory bowel disease, patient-reported symptoms frequently do not correlate with endoscopic or histologic degree of intestinal inflammation 1.

References

1
Guideline

Risk Assessment and Clinical Features for Crohn Disease and Hereditary Polyposis Syndromes

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

3
Research

Peutz-Jeghers syndrome: diagnostic and therapeutic approach.

World journal of gastroenterology, 2009

5
Research

Ulcerative colitis: pathogenesis, diagnosis, and current treatment.

Journal of the Association for Academic Minority Physicians : the official publication of the Association for Academic Minority Physicians, 1996

6
Guideline

Diagnosis and Treatment of Occult Gastrointestinal Bleeding

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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