High Yield Internal Medicine for the USMLE & ABIM: Intestinal/GI Conditions

Gastroenterology encompasses a vast array of diseases, and it can be a challenge to memorize every little detail. Here are the most high-yield intestinal topics in GI.

Oro-esophageal conditions
Dys-phagia is diff-iculty while odyn-ophagia is pain-ful. Obstructive pathology tends to limit solids, while neuromuscular disorders affect both solids and liquids; a barium swallow or EGD may be indicated to make the specific diagnosis.

Achalasia is an example of a neuromuscular disorder causing impaired esophageal peristalsis and inability to relax the lower esophageal sphincter (LES); diagnosis can be made with barium swallow (“bird’s beak” finding) and/or manometry, while an EGD would be needed to rule out malignancy. Treatments for achalasia can exacerbate GERD due to relaxation of the LES.

Diffuse esophageal spasm (DES) is another neuromuscular disorder, where painful, non-peristaltic contractions of the esophagus occur; manometry will show exactly this, while barium swallow shows a “corkscrew” pattern. CCBs and nitrates can reduce the chest pain and dysphagia of DES.
Zenker diverticulum is an outpouching of the upper esophagus smooth muscle, where regurgitated food can remain for days, causing bad breath (halitosis) and feelings of aspiration; barium swallow will readily elucidate the outpouching, which requires surgical repair.

GERD is caused by low pressure in the LES, where acid moves from the columnar-epithelium-lined stomach into the esophagus causing acidic burns to its squamous epithelium. Patients will present with burning-type chest pain after eating, which is exacerbated by heavy meals and lying down after eating. Risk factors include obesity, hiatal hernia, pregnancy, and scleroderma. The diagnosis can be made clinically from the history alone, but red flags may be present to warrant an EGD to evaluate for Barrett esophagus and/or adenocarcinoma. Red flags include weight loss, age >50 years, >5 years of persistent GERD symptoms. GERD without warning signs can be treated with a trial of a PPI for 4 weeks, which also serves as a diagnostic therapy.Peptic ulcer disease (PUD)
Excess stomach acidity can erode the gastric and duodenal mucosa. H pylori is involved in most gastric and almost all duodenal ulcers. A patient often complains of epigastric pain that changes after meals (duodenal improves due to increased bicarbonate secretion, while gastric worsens). Look for a history of NSAID or steroid use, tobacco smoking, or alcohol use. Lab workup includes a urea breath test and a CBC to evaluate for severity of bleeding. Severe bleeding should be treated like any GI bleed with consideration of a perforation (a surgical emergency). Patients with H pylori infection are at an increased risk of GI lymphoma, and treatment includes PPI with clarithromycin and amoxicillin/metronidazole.GI Bleeding
Upper and lower are differentiated by their relation to the ligament of Treitz. Most are upper GI bleeds (UGIB), which can present as melena (dark, tarry stools) from a slow bleed or hematochezia (bright) from a fast bleed. The BUN can help differentiate the etiology of hematochezia: UGIB allows for reabsorption of urea from the blood and a high BUN:Cr (>20), whereas LGIB would have a normal ratio. Hematochezia from UGIB would likely have enough blood loss to cause hemodynamic instability and possibly hemorrhagic shock.

The most common causes of UGIB are PUD, mallory-weiss tear, esophageal varices, and gastritis. The most common causes of LGIB are diverticulosis/diverticulitis, colon cancer, ulcerative colitis, mesenteric ischemia, arteriovenous malformations (AVMs), and hemorrhoids.
Patients may need to be stabilized prior to EGD and/or colonoscopy. This includes aggressive fluid resuscitation and transfusions to maintain a hemoglobin. IV PPI should be started as well. With bleeding varices, a somatostatin analog (ie- octreotide) should be used for vasoconstriction; for a cirrhotic patient, antibiotics should also be administered for SBP prophylaxis.Pancreatitis
Acute pancreatitis is most caused by gallstones, followed by alcohol, then hypertriglyceridemia, and other etiologies including medications. The diagnosis of pancreatitis is made with a consistent history, labs, and sometimes imaging; this includes epigastric abdominal pain radiating to the back with a lipase >3x upper limit of normal, and a CT with pancreatic inflammation can support the diagnosis if one of these is missing. The key to management in pancreatitis is aggressive fluids for the first 24-48 hours; think of the pancreas as a black hole that sucks in intravascular fluid, which can lead to hypotension/shock and can also cause ARDS.
Chronic pancreatitis is most caused by alcohol abuse with a history of multiple episodes of acute pancreatitis. The pancreas has burned out of its enzymes, and patients present with weight loss and steatorrhea which improves with enzyme supplementation. Imaging may show pancreatic calcifications.Intestinal conditions
Celiac disease is an immune-mediated genetic disorder with gluten intolerance. Anti-tisssue transglutaminase (TTG) IgA and anti-endomysal IgA damage the small intestine mucosa. Presentations can be widely variable at seemingly any age, but common signs are bloating, diarrhea, and weight loss. Dermatitis herpetiformis is an associated skin finding. SI biopsy shows blunting of duodenal and jejunal villi. Treatment is a gluten free diet.
Mesenteric ischemia can be acute or chronic. Acute mesenteric ischemia presents as severe abdominal pain out of proportion to physical exam findings; it is caused by vascular compromise such as an embolic event. Chronic mesenteric ischemia presents in vasculopathic patients (history of DM, smoker, CAD, stroke, etc) as abdominal pain after eating.

Diverticulosis is outpouching of the colon due to increased pressures and stool burden, usually in older patients with low fiber/water diets. Diverticulitis presents as left lower quadrant (LLQ) abdominal pain and distention, possibly with hematochezia. Complications include perforation or abscess formation, and treatment includes antibiotics. Patients should be referred for colonoscopy once the episode has resolved.Inflammatory bowel disease