Celiac Disease
IgA anti-tissue transglutaminase (tTG); duodenal biopsy shows intraepithelial lymphocytosis, crypt hyperplasia, and villous blunting; dermatitis herpetiformis.
Whipple Disease
Tropheryma whipplei; PAS-positive macrophages in lamina propria; CAN triad (Cardiac, Arthralgias, Neurologic) + malabsorption; treat with IV Ceftriaxone -> TMP-SMX.
CRC Screening Standard
Average risk: begins at age 45 (colonoscopy every 10 years). First-degree relative < 60: start at age 40 or 10 years before youngest relative's diagnosis.
Lynch Syndrome (HNPCC)
Autosomal dominant germline mutation in DNA mismatch repair genes (MLH1, MSH2); microsatellite instability; 80% risk of CRC + Endometrial cancer.
Malabsorption Syndromes: Celiac vs. Whipple vs. SIBO
| Condition | Etiology / Genetics | Biopsy & Diagnostic Findings | Extraintestinal Symptoms & Treatment |
|---|---|---|---|
| Celiac Disease (Gluten Enteropathy) | Autoimmune intolerance to gliadin; HLA-DQ2 and HLA-DQ8 | IgA anti-tTG (tissue transglutaminase) and anti-endomysial; Duodenal biopsy: villous atrophy, crypt hyperplasia | Dermatitis herpetiformis (pruritic vesicular rash on extensor surfaces; granular IgA in dermal papillae; treated with Dapsone); Strict gluten-free diet |
| Whipple Disease | Infection by actinomycete Tropheryma whipplei | Small bowel biopsy: PAS-positive, diastase-resistant foamy macrophages containing rod-shaped bacilli | Weight loss, migratory arthralgias, lymphadenopathy, hyperpigmentation, neurologic symptoms (dementia, oculomasticatory myorhythmia); IV Ceftriaxone -> oral TMP-SMX for 1 year |
| Small Intestinal Bacterial Overgrowth (SIBO) | Anatomical or motility disorders (scleroderma, diabetes gastroparesis, blind loops) | Carbohydrate breath test (positive lactulose / glucose hydrogen breath test) | Bloating, flatulence, B12 deficiency (bacterial consumption) with elevated folate levels; oral Rifaximin |
Colorectal Polyps & Hereditary Cancer Syndromes
| Syndrome / Polyp Type | Genetic Mutation & Pathway | Histology & Malignant Potential | Surveillance Strategy |
|---|---|---|---|
| Adenomatous Polyps | Adenoma-Carcinoma Sequence: APC mutation (loss of intercellular adhesion) -> KRAS (uncontrolled growth) -> p53 / DCC (carcinomatous invasion) | Tubular (least risk, < 25% villous), Tubulovillous (intermediate), Villous adenoma (highest malignant potential, > 50% villous) | Complete polypectomy; repeat colonoscopy in 3 to 5 years depending on size (≥ 10 mm), number (≥ 3), and histology |
| Familial Adenomatous Polyposis (FAP) | Autosomal dominant mutation in APC tumor suppressor gene on chromosome 5q21 | Thousands of adenomatous polyps covering colorectal mucosa; 100% progress to colorectal cancer by age 40 | Annual sigmoidoscopy starting at age 10–12; prophylactic total proctocolectomy mandatory |
| Lynch Syndrome (HNPCC) | Autosomal dominant mutation in DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2) | Microsatellite Instability (MSI); proximal / right-sided colon cancer predominance | Colonoscopy every 1–2 years starting at age 20–25; annual endometrial biopsy or prophylactic hysterectomy/oophorectomy |
OMM Board Correlate: Middle & Lower GI Autonomics
- Autonomic Transition at Splenic Flexure: Proximal 2/3 of transverse colon innervated by SMG (T10–T11) and Vagus (CN X). Distal 1/3 of transverse colon to rectum innervated by IMG (T12–L2) and Pelvic Splanchnics (S2–S4).
- Chapman Points for Colon: Anterior points form an inverted triangle ('iliotibial band / strip') along the anterior aspect of the IT band from greater trochanter to just above knee. Posterior points between transverse processes of L2–L4.
- Sacral Rocking: Gentle rhythmic rocking of the sacral base between inhalation and exhalation normalizes parasympathetic tone to the lower bowel, treating ileus and constipation.
Board Traps & Common Distractors
- Any adult male or postmenopausal female presenting with new iron deficiency anemia has Colorectal Cancer until proven otherwise; prompt colonoscopy and upper endoscopy are mandatory.
- Patients with Celiac Disease who strictly adhere to a gluten-free diet but develop refractory weight loss, diarrhea, and fever must be evaluated for Enteropathy-Associated T-Cell Lymphoma (EATL).
- In patients with severe acute diverticulitis, colonoscopy and barium enema are strictly CONTRAINDICATED during the acute phase due to high risk of bowel perforation and peritonitis; perform CT abdomen/pelvis with IV contrast.