Gastroenterology · Inflammatory Bowel Disease
The facts most likely to be tested
Crohn disease presents with transmural inflammation that can involve any part of the gastrointestinal tract from the mouth to the anus with skip lesions.
Endoscopic evaluation reveals cobblestoning of the mucosa and creeping fat on surgical inspection.
Histopathology is characterized by non-caseating granulomas, which are pathognomonic for Crohn disease.
Patients frequently present with right lower quadrant pain and a palpable mass due to terminal ileum involvement, often mimicking acute appendicitis.
Complications include fistulas, sinus tracts, abscesses, and strictures leading to small bowel obstruction.
Extraintestinal manifestations include uveitis, erythema nodosum, pyoderma gangrenosum, and ankylosing spondylitis.
Smoking is a significant risk factor that exacerbates disease severity and increases the risk of recurrence after surgical resection.
Vignette unlocked
A 24-year-old female presents with 3 months of non-bloody diarrhea, postprandial abdominal pain, and a 10-lb unintentional weight loss. Physical examination reveals a tender right lower quadrant mass and a small perianal skin tag. Laboratory studies show an elevated erythrocyte sedimentation rate and mild iron deficiency anemia. Colonoscopy demonstrates skip lesions with intervening areas of normal mucosa in the ascending colon.
What is the most likely diagnosis?
Crohn disease
The patient's presentation of transmural involvement, skip lesions, and perianal disease is classic for Crohn disease, which is supported by the presence of a right lower quadrant mass indicating terminal ileum involvement.
Full handout
High yield triage
Etiology / Epidemiology
Bimodal distribution (15-35, 55-70) with strong genetic predisposition and smoking as a major risk factor.
Clinical Manifestations
Transmural inflammation causing skip lesions and cobblestoning; presents with RLQ pain and non-bloody diarrhea.
Diagnosis
Colonoscopy with biopsy is the gold standard; look for transmural inflammation and non-caseating granulomas.
Treatment
Corticosteroids for acute flares; anti-TNF agents (e.g., infliximab) for maintenance; avoid smoking.
Prognosis
High risk of fistula formation and strictures; requires lifelong monitoring for colorectal cancer.
Full handout
Epidemiology & Etiology
Peak incidence occurs in young adults with a secondary peak in the 6th decade. Smoking is the most significant modifiable risk factor, paradoxically worsening Crohn disease while potentially protective in ulcerative colitis. Genetic linkage to the NOD2 gene mutation is frequently observed.
Pertinent Anatomy
Can affect any segment of the GI tract from mouth to anus, but most commonly involves the terminal ileum. Characterized by skip lesions (normal tissue interspersed with diseased segments) and transmural involvement.
Pathophysiology
Chronic immune-mediated inflammation leads to transmural damage, resulting in deep ulcerations and cobblestoning of the mucosa. The inflammatory process triggers fibrosis and stricture formation, leading to obstructive symptoms. The presence of non-caseating granulomas is a hallmark histological finding.
Clinical Manifestations
Patients present with chronic non-bloody diarrhea, weight loss, and RLQ abdominal pain mimicking appendicitis. Physical exam may reveal a palpable mass or signs of perianal disease, including fistulas, fissures, and abscesses. Red flags include fever, severe dehydration, and signs of bowel obstruction.
Diagnosis
Colonoscopy with biopsy is the gold standard for visualization and tissue confirmation. CT enterography is the preferred imaging modality to evaluate for small bowel involvement, strictures, or abscesses. Biopsy findings of non-caseating granulomas are pathognomonic.
Treatment
Acute flares are managed with corticosteroids (e.g., budesonide or prednisone) to induce remission. Maintenance therapy utilizes anti-TNF agents (e.g., infliximab, adalimumab) or immunomodulators like azathioprine. Contraindications for anti-TNF therapy include active infection or latent tuberculosis; screen with PPD/IGRA prior to initiation.
Prognosis
Disease is chronic and relapsing, with high rates of fistula, abscess, and stricture formation requiring surgical intervention. Patients have an increased risk of colorectal cancer, necessitating regular surveillance colonoscopy starting 8 years after diagnosis.
Differential Diagnosis
Ulcerative Colitis: continuous mucosal inflammation limited to the colon
Infectious Colitis: acute onset, usually self-limiting, positive stool cultures
Irritable Bowel Syndrome: diagnosis of exclusion, no inflammatory markers
Appendicitis: acute onset, localized RLQ tenderness, no chronic diarrhea
Celiac Disease: malabsorption triggered by gluten, villous atrophy on biopsy