USMLE Guide: Ulcerative Colitis

Introduction

Ulcerative colitis (UC) is a chronic inflammatory bowel disease (IBD) that primarily affects the colon and rectum. It is characterized by recurring episodes of inflammation and ulceration, leading to various gastrointestinal symptoms. This USMLE guide aims to provide a comprehensive overview of ulcerative colitis, including its etiology, clinical presentation, diagnostic approach, and treatment options.

Etiology

The exact cause of ulcerative colitis remains unknown, but several factors contribute to its development:

• Genetics: There is a strong genetic predisposition for UC, with certain human leukocyte antigen (HLA) types being associated with an increased risk.
• Immunological factors: Dysregulated immune response in the gut, particularly involving T cells and cytokine imbalance, plays a significant role in UC pathogenesis.
• Environmental factors: Although not fully understood, environmental factors such as smoking, diet, and exposure to certain infectious agents may contribute to the development of UC.

Clinical Presentation

Patients with ulcerative colitis commonly present with the following clinical features:

• Diarrhea: Bloody diarrhea is a hallmark symptom of UC, often accompanied by urgency and tenesmus.
• Abdominal pain: Crampy abdominal pain, typically localized in the left lower quadrant, is frequently reported.
• Rectal bleeding: Hematochezia is common in UC due to the inflammation and ulceration of the rectum.
• Weight loss: Chronic inflammation and malabsorption can lead to unintended weight loss.
• Extraintestinal manifestations: UC may involve extraintestinal organs, leading to manifestations such as arthritis, uveitis, erythema nodosum, or pyoderma gangrenosum.

Diagnostic Approach

The diagnosis of ulcerative colitis involves a combination of clinical evaluation, laboratory tests, endoscopic examination, and histological findings. The following diagnostic approach is commonly followed:

1. Clinical evaluation: Detailed history-taking and physical examination to assess symptoms, disease duration, and extraintestinal manifestations.
2. Laboratory tests: Complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and stool studies (to exclude infectious causes of colitis).
3. Endoscopic examination: Flexible sigmoidoscopy or colonoscopy with mucosal biopsy is essential for visualizing the inflamed colonic mucosa and obtaining histological samples.
4. Histological findings: Microscopic examination of the biopsied tissue helps confirm the presence of characteristic features such as crypt distortion, ulceration, and inflammatory infiltrates.

Treatment Options

The management of ulcerative colitis aims to induce and maintain remission while minimizing symptoms and complications. Several treatment modalities are available:

1. Aminosalicylates: Oral or topical 5-aminosalicylates (5-ASA) are commonly used as first-line therapy for mild to moderate UC.
2. Corticosteroids: Systemic corticosteroids are reserved for moderate to severe UC flare-ups that do not respond to 5-ASA. Topical corticosteroids may be used for distal disease.
3. Immunomodulators: Thiopurines (azathioprine, mercaptopurine) and methotrexate are used as steroid-sparing agents and for maintenance therapy.
4. Biologic agents: Tumor necrosis factor-alpha (TNF-alpha) inhibitors (e.g., infliximab, adalimumab) and other biologic agents targeting different pathways (e.g., vedolizumab, ustekinumab) are reserved for moderate to severe UC that does not respond to conventional therapy.
5. Surgery: In refractory cases or complications (e.g., toxic megacolon, colon cancer), surgical intervention (partial or total colectomy) may be necessary.

Conclusion

Ulcerative colitis is a chronic inflammatory bowel disease characterized by inflammation and ulcers in the colon and rectum. Understanding the etiology, clinical presentation, diagnostic approach, and treatment options is crucial for medical professionals evaluating and managing patients with UC. By following this USMLE guide, you can gain a solid foundation in ulcerative colitis knowledge and be better prepared for related questions in your examination.