GI in the Immunocompromised Host

• Audio chapter
  Single-voice audio, listen on the commute.
• ABIM-format MCQs
  5-option vignettes with full wrong-answer teaching.
• Study guide
  Tables, decision trees, primary sources.
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What this chapter covers

• Section 34.1: Solid organ transplant GI disease

  Solid organ transplant recipients carry a five-drug differential at every GI symptom: cytomegalovirus, mycophenolate enteropathy, calcineurin inhibitor toxicity, post-transplant lymphoproliferative disorder driven by Epstein-Barr virus, and Clostridioides difficile.

• Section 34.2: HCT and acute gut graft-versus-host disease

  Approximately 20,000 allogeneic hematopoietic cell transplants are performed in the United States each year.

• Section 34.3: HIV host framework and HIV-era GI

  This section covers HIV as a host factor and the GI presentations that depend on immune status rather than on a specific pathogen.

• Section 34.4: Checkpoint inhibitor colitis

  Immune checkpoint inhibitors targeting CTLA-4 (ipilimumab, tremelimumab) and PD-1 or PD-L1 (nivolumab, pembrolizumab, cemiplimab, atezolizumab, durvalumab) unleash T-cell responses against tumor antigens but also against self tissue.

• Section 34.5: Checkpoint inhibitor hepatitis and other irAEs

  Checkpoint inhibitor hepatitis affects approximately 4 to 9 percent of patients on anti-CTLA-4 monotherapy, 1 to 4 percent on anti-PD-1 or anti-PD-L1 monotherapy, and up to 18 percent on combination ipilimumab plus nivolumab.

• Section 34.6: Neutropenic enterocolitis (typhlitis)

  Neutropenic enterocolitis presents in patients with absolute neutrophil count below 500 cells per microliter (especially under 100) receiving cytotoxic chemotherapy, most often during acute leukemia induction (cytarabine for acute myeloid leukemia, intensive regimens for pediatric acute lymphoblastic leukemia).

Podcast episodes

1. 01

   GI in the Immunocompromised Host: Organ Transplant

   Every GI symptom in a solid organ transplant recipient is weighed against five causes: CMV, mycophenolate enteropathy, calcineurin inhibitor toxicity, EBV-driven post-transplant lymphoproliferative disorder, and C. difficile. Time since transplant narrows the list. The episode follows a kidney recipient with diarrhea, covering how CMV is prevented by serostatus and organ, how CMV colitis is diagnosed by biopsy and treated, how mycophenolate injury is separated from CMV and managed, and how a new azole drives tacrolimus toxicity. It closes with a liver recipient with a small bowel mass, showing when PTLD responds to less immunosuppression and rituximab and when it needs chemotherapy.

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2. 02

   GI in the Immunocompromised Host: Gut in Leukemia

   The episode follows one woman with acute myeloid leukemia, and the organizing idea is that timing and the failed barrier of the gut decide the diagnosis and the treatment. During induction chemotherapy, neutropenic enterocolitis is confirmed with CT rather than colonoscopy, treated with bowel rest and antibiotics that cover gram-negatives, anaerobes, and Pseudomonas, then widened to antifungals after seventy-two hours of fever, with surgery reserved for complications. After allogeneic transplant, days since transplant narrow the cause of diarrhea. Gut graft-versus-host disease is staged by stool volume, proven by rectosigmoid biopsy with CMV excluded, treated with methylprednisolone, and escalated to ruxolitinib if steroids fail.

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3. 03

   GI in the Immunocompromised Host: HIV as a Host

   The organizing idea is that in HIV the CD4 count, more than any single organism, sets the GI differential, and antiretroviral therapy is the main treatment for most of what follows. The episode follows a newly diagnosed man with a CD4 count of forty. It starts with the CD4 tiers and the workup they dictate, then AIDS cholangiopathy, where papillary stenosis still needs a sphincterotomy. Next is Kaposi sarcoma, recognized by appearance and confirmed with LANA-1 staining when pinch biopsies are normal. It then covers when to start antiretroviral therapy, how to handle immune reconstitution inflammatory syndrome with MAC, and why routine MAC prophylaxis is not given when effective therapy is starting.

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4. 04

   GI in the Immunocompromised Host: Checkpoint Drugs

   Checkpoint inhibitors release T cells against tumor and also against the gut and liver, so the episode asks which drug, which organ, and which grade. For colitis, it moves from regimen and timing to excluding C. difficile, and CMV after steroids, then endoscopy, stool-frequency grading, steroids, and the seventy-two hour decision to add infliximab or vedolizumab. It then covers restarting by drug class and microscopic colitis. For hepatitis, it covers workup, biopsy versus autoimmune hepatitis, grading by ALT and bilirubin, steroid taper, mycophenolate instead of infliximab, and re-challenge. It closes with the cholangitic variant, pancreatic, gastric, and endocrine events, and board traps.

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Key topics

• ·Five causes of GI symptoms after transplant
• ·Time since transplant and the differential
• ·CMV risk by donor and recipient serostatus
• ·CMV prophylaxis duration by organ
• ·CMV colitis diagnosis and treatment
• ·Mycophenolate enteropathy
• ·Tacrolimus toxicity and drug interactions
• ·Calcineurin inhibitor toxicity and mTOR inhibitors
• ·Post-transplant lymphoproliferative disorder
• ·Board traps in transplant GI
• ·Neutropenic enterocolitis (typhlitis)
• ·CT instead of colonoscopy
• ·Antibiotic coverage for cecal flora
• ·Empiric antifungals and surgical indications
• ·Calendar of post-transplant GI complications
• ·Acute graft-versus-host disease risk factors
• ·Glucksberg-Seattle staging by stool volume
• ·MAGIC biomarkers
• ·Rectosigmoid biopsy and CMV exclusion
• ·Steroids and ruxolitinib for refractory disease
• ·CD4 count tiers and the GI differential
• ·Workup of diarrhea at a CD4 count of forty
• ·AIDS cholangiopathy causes and ERCP patterns
• ·Papillary stenosis and sphincterotomy
• ·Kaposi sarcoma and human herpesvirus eight
• ·LANA-1 staining after a normal biopsy
• ·Antiretroviral therapy as main treatment
• ·Timing of antiretroviral therapy and cryptococcal meningitis
• ·Immune reconstitution inflammatory syndrome and MAC
• ·MAC prophylaxis and board traps