Malabsorption And Inflammatory Bowel Disease - USMLE Step 2

1. Which of the following is the most appropriate test to monitor her dietary adherence and response to therapy?
   Answer: IgA anti-tissue transglutaminase antibody titer Serologic markers, particularly IgA anti-tissue transglutaminase (tTG) antibodies, are used to monitor response to a gluten-free diet in patients with celiac disease. With strict dietary adherence, these antibody titers should decrease significantly and eventually normalize, usually within 6-12 months. Persistently elevated titers suggest ongoing gluten exposure. A repeat biopsy is generally reserved for patients who do not respond symptomatically or serologically to the diet. Total IgA is checked at diagnosis to rule out IgA deficiency but is not used for monitoring.
2. These endoscopic findings are most consistent with a diagnosis of:
   Answer: Ulcerative colitis The endoscopic findings described are classic for ulcerative colitis. Key features include: 1) inflammation starting in the rectum (proctitis), 2) continuous inflammation extending proximally without intervening normal mucosa ('skip lesions'), and 3) absence of small bowel involvement. Crohn disease is typically characterized by skip lesions, rectal sparing, deeper ulcers, and frequent terminal ileum involvement. Ischemic and infectious colitis can have varied appearances but do not typically present with this chronic, continuous pattern starting in the rectum.
3. This patient is at most immediate risk for which of the following complications?
   Answer: Perforation The clinical picture of severe colonic dilation (transverse colon > 6 cm) accompanied by signs of systemic toxicity (fever, leukocytosis) is diagnostic of toxic megacolon. This is a life-threatening complication of severe colitis, most commonly seen in ulcerative colitis. The inflamed, dilated, and thinned bowel wall is at high risk for perforation, which can lead to peritonitis, sepsis, and death. Therefore, perforation is the most immediate and feared complication requiring urgent surgical consultation.
4. This patient's malabsorption is most likely caused by a deficiency of which of the following?
   Answer: Pancreatic lipase The patient's history of chronic pancreatitis combined with clinical signs of fat malabsorption (steatorrhea) and a positive quantitative fecal fat test points to exocrine pancreatic insufficiency (EPI). In EPI, the pancreas fails to produce adequate amounts of digestive enzymes. The deficiency of pancreatic lipase leads to impaired digestion of dietary fats, resulting in steatorrhea and weight loss. Bile salt deficiency causes fat malabsorption but is less likely given the history. Lactase deficiency causes osmotic diarrhea, not steatorrhea. Intrinsic factor deficiency causes vitamin B12 malabsorption.
5. Which of the following is the most appropriate initial step in this patient's management?
   Answer: Obtain a CT scan of the abdomen and pelvis with contrast. This patient's presentation is highly suspicious for an intra-abdominal abscess, a known complication of penetrating Crohn disease. The first step in management is to confirm the diagnosis and delineate the anatomy of the abscess. A CT scan of the abdomen and pelvis with intravenous and oral contrast is the imaging modality of choice for this purpose. It will confirm the presence, size, and location of the abscess and help guide subsequent therapy, which typically involves percutaneous drainage and broad-spectrum antibiotics. Starting immunosuppressants like prednisone or infliximab is contraindicated in the setting of an undrained abscess.
6. Which of the following is the most appropriate next step in diagnosis and management?
   Answer: Trial of a lactose-free diet The patient's symptoms are classic for lactose intolerance, a condition caused by lactase deficiency. The symptoms are directly related to the ingestion of dairy products and resolve with avoidance. In a patient with such a clear history, the most practical, cost-effective, and appropriate next step is an empiric trial of a lactose-free diet. This serves as both a diagnostic test and a therapeutic intervention. More invasive or expensive tests like endoscopy or serology for celiac disease would be considered if symptoms persisted despite dietary changes or if there were red flag symptoms (e.g., weight loss, bleeding).
7. Which of the following is the most appropriate next step in management?
   Answer: Add an anti-TNF biologic agent. This patient has moderate-to-severe Crohn disease that is refractory to 5-aminosalicylic acid (5-ASA) therapy (mesalamine). For such patients, the next step in management is to escalate therapy. Biologic agents, such as anti-TNF therapy (e.g., infliximab, adalimumab), are highly effective for inducing and maintaining remission in moderate-to-severe Crohn disease. Increasing the mesalamine dose or switching to another 5-ASA like sulfasalazine is unlikely to be effective. Antibiotics are used for infectious complications like abscesses or for some cases of perianal disease, not for uncomplicated luminal inflammation.
8. Which of the following is the most appropriate next step to confirm the diagnosis?
   Answer: Obtain an upper endoscopy with small bowel biopsy. This patient's presentation of chronic diarrhea, weight loss, and iron deficiency anemia, along with positive IgA anti-tissue transglutaminase antibodies, is highly suggestive of celiac disease. The gold standard for confirming the diagnosis is an upper endoscopy with multiple biopsies from the distal duodenum, which classically show villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. It is crucial to perform the biopsy before the patient starts a gluten-free diet, as the intestinal mucosa can heal and lead to a false-negative result.
9. Which of the following is the most likely diagnosis for his ocular symptoms?
   Answer: Anterior uveitis Anterior uveitis (or iritis) is one of the most common extraintestinal manifestations of inflammatory bowel disease. The classic presentation includes eye pain, photophobia, blurred vision, and conjunctival injection. The definitive finding on slit-lamp examination is the presence of inflammatory cells in the anterior chamber. Unlike peripheral arthritis, the activity of uveitis is often independent of the activity of the underlying bowel disease. Episcleritis is more common but presents with painless redness. Scleritis causes deep, boring pain. Glaucoma is characterized by increased intraocular pressure.
10. This patient's hepatobiliary condition is most strongly associated with which of the following underlying diagnoses?
    Answer: Ulcerative colitis The patient's clinical presentation and ERCP findings are classic for primary sclerosing cholangitis (PSC). PSC is a chronic cholestatic liver disease characterized by inflammation and fibrosis of the bile ducts. There is a very strong association between PSC and inflammatory bowel disease, particularly ulcerative colitis. Approximately 70-80% of patients with PSC have underlying ulcerative colitis. While PSC can occur with Crohn disease, the association is much weaker.
11. The onset of this patient's condition after smoking cessation is a well-described phenomenon associated with which of the following?
    Answer: Ulcerative colitis Smoking has a paradoxical and opposing effect on the two main types of IBD. It is a significant risk factor for the development and worsening of Crohn disease. Conversely, smoking appears to be protective against ulcerative colitis. It is a well-recognized clinical observation that a subset of patients develop ulcerative colitis for the first time or experience a significant flare of their disease shortly after quitting smoking. The colonoscopy findings of continuous distal inflammation are also consistent with ulcerative colitis.
12. Which of the following is the most appropriate initial medical therapy for his fistulizing disease?
    Answer: Metronidazole For simple, asymptomatic or mildly symptomatic perianal fistulas in Crohn disease, a course of antibiotics is often the first-line medical therapy. Metronidazole, with or without ciprofloxacin, can help reduce fistula drainage and inflammation. Biologic agents like infliximab are highly effective but are typically reserved for more complex, symptomatic, or refractory fistulas due to cost and potential side effects. Topical steroids and oral mesalamine are ineffective for treating fistulizing Crohn disease.
13. This patient's dermatologic findings are most likely due to a deficiency of which of the following micronutrients?
    Answer: Zinc The patient has short bowel syndrome secondary to multiple resections of the terminal ileum for Crohn disease, leading to malabsorption. His clinical presentation of a periorificial and acral dermatitis (acrodermatitis enteropathica-like), alopecia, and diarrhea is classic for zinc deficiency. The terminal ileum is a major site of zinc absorption. While he is also at high risk for vitamin B12 deficiency (absorbed in the terminal ileum) and iron deficiency, these do not cause this characteristic rash.
14. Which of the following is the most appropriate initial therapy?
    Answer: Intravenous corticosteroids This patient presents with a severe flare of ulcerative colitis, as evidenced by frequent bloody stools (>6/day), fever, tachycardia, and anemia (Truelove and Witts' criteria). The standard of care for a severe UC flare is hospitalization and initiation of intravenous corticosteroids (e.g., hydrocortisone or methylprednisolone). Oral therapies are inadequate for severe disease, and biologic agents like adalimumab are typically reserved for outpatients with moderate disease or inpatients who are refractory to IV steroids. Loperamide is contraindicated as it can precipitate toxic megacolon.
15. Which of the following is the most appropriate primary management strategy for her arthritis?
    Answer: Control the underlying intestinal inflammation. This patient has an extraintestinal manifestation of IBD, specifically a type 1 (pauciarticular) peripheral arthropathy. The clinical activity of this type of arthritis directly mirrors the activity of the underlying bowel disease. Therefore, the cornerstone of management is to treat and control the intestinal inflammation of her Crohn disease. As her bowel disease improves, her arthritis is expected to resolve. NSAIDs like naproxen should be used with extreme caution or avoided in IBD as they can trigger disease flares. Intra-articular steroids can provide temporary relief but do not address the root cause.
16. Which of the following is the most concerning potential diagnosis in this patient?
    Answer: Enteropathy-associated T-cell lymphoma This patient's presentation of new, severe symptoms ('alarm symptoms' like weight loss and pain) after a long period of well-controlled celiac disease is highly concerning for a malignancy. Enteropathy-associated T-cell lymphoma (EATL) is a rare but well-known complication of long-standing celiac disease. The endoscopic findings of ulceration are also suspicious. While other conditions like refractory celiac disease or SIBO are possible, the severity of the presentation makes EATL the most urgent and concerning diagnosis to exclude.
17. Which of the following is the most appropriate initial treatment to induce remission?
    Answer: Topical mesalamine enema For mild-to-moderate distal ulcerative colitis (proctitis or proctosigmoiditis), topical therapy with a 5-aminosalicylic acid (5-ASA) agent is the first-line treatment. Mesalamine enemas can reach the sigmoid colon and are more effective than oral 5-ASA agents for distal disease because they deliver a higher concentration of the active drug to the site of inflammation. Systemic corticosteroids (prednisone), immunomodulators (azathioprine), and biologics (infliximab) are reserved for more extensive or severe disease.
18. These histologic findings are most characteristic of which of the following conditions?
    Answer: Crohn disease The presence of noncaseating granulomas on biopsy is a classic, though not universal, feature of Crohn disease. Transmural inflammation (involving all layers of the bowel wall) is also a hallmark of Crohn disease. In contrast, ulcerative colitis is characterized by inflammation limited to the mucosa and submucosa, and granulomas are rare. Celiac disease affects the small intestine with villous atrophy. Microscopic colitis shows either lymphocytic infiltration or a thickened collagen band, not granulomas.
19. A skin biopsy confirms dermatitis herpetiformis. This condition is a cutaneous manifestation of which of the following underlying gastrointestinal disorders?
    Answer: Celiac disease Dermatitis herpetiformis (DH) is a pathognomonic extraintestinal manifestation of celiac disease. It is caused by the deposition of IgA antibodies in the dermal papillae, which triggers an inflammatory response. The vast majority of patients with DH have histologic evidence of celiac disease on small bowel biopsy, even if they do not have overt gastrointestinal symptoms. Management involves both a strict gluten-free diet and medications like dapsone for symptomatic relief of the rash.
20. According to current guidelines, which of the following is the most appropriate recommendation regarding colorectal cancer screening for this patient?
    Answer: Begin surveillance colonoscopy now, with repeat examinations every 1-2 years. Patients with long-standing, extensive inflammatory bowel disease (involving more than the rectum) are at increased risk for colorectal cancer. Surveillance colonoscopy is recommended to begin 8-10 years after the initial diagnosis. This patient was diagnosed 8 years ago with pancolitis, so it is appropriate to begin surveillance now. The frequency of subsequent colonoscopies (typically every 1-3 years) depends on prior findings, disease activity, and other risk factors. Fecal testing is not sufficient for surveillance in IBD.

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