GI in the Immunocompromised Host: HIV GI Disease and Typhlitis

0:00Welcome to Board Pearls. This is episode three of four of the GI in the Immunocompromised Host chapter, in the Special Populations and Acute or Supportive Care module. In this episode we cover HIV-era GI disease and neutropenic enterocolitis: the CD4-stratified opportunistic infection differential, the ART-related GI effects and post-ART immune reconstitution syndrome, and typhlitis as the chemotherapy-related neutropenic enterocolitis with conservative management for stable patients and surgery reserved for perforation, persistent hemorrhage, or clinical deterioration.

0:36The non-transplant immunocompromised GI host runs on two settings that look unrelated until you see what they share. Both ask you to identify the host state first and then ask what differential that host state opens. In HIV the host state is described by a number, the CD4 count. In chemotherapy-related neutropenia the host state is described by another number, the absolute neutrophil count. The number tells you what can go wrong and therefore what to look for.

1:05Start with HIV. About 1.2 million people in the United States live with HIV, and effective antiretroviral therapy has made the classic AIDS-era GI infections uncommon. They have not disappeared. They reappear in newly diagnosed late presenters and in patients with poor adherence or treatment failure. The single most useful clinical anchor in HIV GI is the CD4 count, because the count converts a long pathogen list into a tiered differential that drives workup.

1:39Above five hundred cells per microliter the differential is essentially the same as in an immunocompetent host. Between two hundred and five hundred, oropharyngeal candidiasis emerges as the first opportunistic finding. Below two hundred, herpes simplex ulcers, esophageal candidiasis, and Cystoisospora become probable. Below one hundred, Cryptosporidium, microsporidia, and cytomegalovirus enter as the highest-risk-organism tier. Below fifty, disseminated cytomegalovirus and disseminated Mycobacterium avium complex appear.

2:12The implication is that the pretest probability of every GI symptom changes with the CD4 stratum. A patient with chronic watery diarrhea and a CD4 of four hundred is not the same problem as a patient with chronic watery diarrhea and a CD4 of forty. The first patient gets the routine chronic diarrhea workup. The second patient gets directed stool studies for Cryptosporidium and microsporidia, blood cultures for Mycobacterium avium complex, and an early plan for endoscopy with biopsies if studies are unrevealing. The pathogen-level diagnostic and treatment detail for those organisms lives in the GI Infections chapter, because this chapter owns the host framework rather than the bug-by-bug regimen.

2:56Three pre-antiretroviral-era entities still appear in late presenters, and the boards keep testing them. The first is AIDS cholangiopathy.

3:05AIDS cholangiopathy was a defining presentation of the pre-antiretroviral era, occurring in about a quarter of late-stage AIDS patients with CD4 below one hundred. It is now uncommon. The etiology, in approximate order of frequency, is Cryptosporidium parvum first, then microsporidia, then cytomegalovirus, then Cyclospora. Patients present with right upper quadrant or epigastric pain plus diarrhea. Fever and jaundice are less common than in classical biliary obstruction, which is one of the recognition cues.

3:40ERCP shows three patterns. Sclerosing cholangitis with papillary stenosis is the most common. Sclerosing cholangitis alone and papillary stenosis alone make up the rest. Treatment is antiretroviral therapy as the dominant intervention, with ERCP sphincterotomy added for symptomatic papillary stenosis and pathogen-specific therapy directed at whichever organism the workup identifies.

4:05The reason sphincterotomy is the answer for the papillary stenosis pattern specifically, and not just antiretroviral therapy, is worth dwelling on. The stenosis is fixed scarring from prior cryptosporidial inflammation. The inflammation drove a structural narrowing, and once the narrowing is laid down it does not reverse with immune reconstitution. Antiretroviral therapy clears the active infection but cannot remodel scar. Only mechanical sphincter division restores drainage, which is why sphincterotomy is needed when the obstructive lesion is at the papilla.

4:38The second pre-antiretroviral-era entity is Kaposi sarcoma. Kaposi sarcoma is driven by human herpesvirus 8, also called Kaposi sarcoma-associated herpesvirus, and presents in HIV patients with CD4 below two hundred. GI lesions appear as violaceous mucosal nodules anywhere in the tract, most often in the stomach and small bowel. Most lesions are asymptomatic. Bleeding can occur.

5:04The recognition step is the clinical appearance, not the biopsy. Pinch biopsy of a typical violaceous nodule is often non-diagnostic because the tumor is submucosal and the pinch samples mucosa above the lesion. The clinical appearance carries the diagnosis at endoscopy, and confirmation uses immunohistochemistry for the latency-associated nuclear antigen 1 of human herpesvirus 8, called LANA-1. Treatment is antiretroviral therapy as the dominant intervention. Lesions depend on HHV-8-driven angiogenic and proliferative signals, and immune reconstitution suppresses those signals by restoring cytotoxic T-cell control of HHV-8-infected cells. Advanced disease that does not regress on antiretroviral therapy alone is treated with intralesional or systemic chemotherapy, with liposomal doxorubicin the preferred systemic agent. The liposomal formulation accumulates in highly vascular tumor, and Kaposi sarcoma is a vascular tumor, which delivers the cytotoxic payload selectively to the lesion.

6:08The third pre-antiretroviral-era entity is the one that appears after antiretroviral therapy starts rather than before. Immune reconstitution inflammatory syndrome, or IRIS, occurs within two to twelve weeks of starting antiretroviral therapy in patients with severe lymphopenia at start. Recovering immune surveillance unmasks or paradoxically worsens an occult or treated infection. The GI presentations include flares of treated Mycobacterium avium complex, cytomegalovirus colitis, hepatic tuberculosis, and Kaposi sarcoma.

6:44The clinical move at IRIS is the opposite of the instinct. The instinct is to assume the antiretroviral regimen is causing harm and to interrupt it. IRIS is a clinical recognition rather than a treatment failure. The management rule is to continue antiretroviral therapy without interruption, treat the underlying opportunistic infection per its own algorithm, and add corticosteroids in severe cases. Interrupting antiretroviral therapy abandons the immune reconstitution that is the durable answer.

7:13The companion rule is the timing of antiretroviral initiation around opportunistic infection diagnosis. The general rule is to start antiretroviral therapy within two weeks of opportunistic infection diagnosis. Earlier initiation reduces mortality and AIDS progression in trials. The major exception is cryptococcal meningitis, where antiretroviral initiation is deliberately delayed by four to six weeks. The reason is IRIS-driven central nervous system mortality. When the unmasked or paradoxically worsened infection is in the central nervous system, the swelling that immune reconstitution drives is catastrophic. Delay buys time for cryptococcal burden to fall before reconstitution adds inflammation to a fixed cranial vault.

7:56One more HIV-era rule belongs in this episode. Primary prophylaxis against disseminated Mycobacterium avium complex in patients with CD4 below fifty historically used azithromycin twelve hundred milligrams orally weekly, or clarithromycin five hundred milligrams orally twice daily. Current United States guidelines no longer routinely recommend primary prophylaxis when patients are initiating effective antiretroviral therapy, because Mycobacterium avium risk falls quickly with viral suppression. The twelve hundred milligram weekly azithromycin regimen remains a board-relevant fact and the historical standard. It is the right answer when the stem describes a patient with CD4 below fifty who is not yet on effective antiretroviral therapy.

8:40That closes the HIV framework. The pattern across all three pre-antiretroviral-era entities is that antiretroviral therapy is the dominant intervention because immune reconstitution restores the cellular control that disease depends on its absence to thrive. Sphincterotomy in AIDS cholangiopathy and liposomal doxorubicin in advanced Kaposi are the exceptions, and the exceptions live where structural scarring or proliferative burden has outrun what immune reconstitution can fix on its own.

9:11Move now to the second setting, which is neutropenic enterocolitis. The clinical name is typhlitis, from typhlon, the Greek word for cecum, because the cecum is where the entity lives.

9:23Typhlitis presents in patients with absolute neutrophil count below five hundred cells per microliter, and especially below one hundred, receiving cytotoxic chemotherapy. The classic setting is acute leukemia induction. Cytarabine for acute myeloid leukemia and the intensive regimens for pediatric acute lymphoblastic leukemia are the canonical exposures. The pathogenesis combines mucosal injury from cytotoxic agents with bacterial or fungal translocation through compromised mucosa. The cecum is particularly vulnerable because it has limited blood supply, it distends easily, and it carries a high bacterial load. Those three features together explain why the cecum is the site, and they explain the name of the entity.

10:10The classic recognition triad is fever, neutropenia with absolute neutrophil count below five hundred, and right lower quadrant pain. Some patients present with right upper quadrant pain, nausea, vomiting, and diarrhea instead, sometimes bloody, depending on the extent of right colon and terminal ileum involvement. The triad is what triggers the diagnostic move. Computed tomography of the abdomen and pelvis with intravenous contrast is the imaging test. Findings are cecal and right colon wall thickening greater than four millimeters, mesenteric fat stranding, occasionally pneumatosis intestinalis, which is gas in the bowel wall, and free air signaling perforation. Pneumatosis suggests advanced ischemic injury and matters because it raises the threshold for surgical involvement.

10:58Colonoscopy is generally contraindicated in active typhlitis. The bowel wall is friable and thinned, and the perforation risk in a neutropenic patient who cannot mount the inflammatory response that ordinarily contains a perforation is unacceptable. The diagnosis is made on imaging and clinical context, not on endoscopic biopsy.

11:20Two differential entries deserve a careful look because they share the chemotherapy-patient host but produce different imaging distributions. Clostridioides difficile colitis in the same patient produces pancolitis or diffuse colitis with relative cecal sparing. Typhlitis is cecum-predominant and may extend to the terminal ileum or ascending colon. The imaging distribution is the first distinguishing tool. The second is C. difficile toxin and PCR testing, which goes on every neutropenic patient with diarrhea regardless of the imaging pattern. Both entities share antibiotic exposure as a risk factor. Both can co-exist in a sick neutropenic patient. The imaging distribution and the toxin result distinguish them, and treatment overlaps but is not identical.

12:06Initial management of typhlitis is conservative. Bowel rest, intravenous fluid resuscitation, electrolyte replacement, and broad-spectrum intravenous antibiotics covering gram-negative organisms, anaerobic flora, and Pseudomonas aeruginosa. The antibiotic spectrum is not arbitrary, and the reason it is the spectrum it is also explains why it sometimes needs a fourth agent.

12:30The cecal pathology arises from breakdown of the mucosal barrier in a neutropenic host. The bacteria crossing the wall are the bacteria that live on the colonic side of the wall: gram-negative coliforms, anaerobes, and Pseudomonas, which colonizes the GI tract in heavily-treated oncology patients on prior antibiotics. The antibiotic choice therefore mirrors the translocating flora. Piperacillin-tazobactam or a carbapenem such as meropenem or imipenem provides this spectrum in a single agent. That is the core of the regimen.

13:06Vancomycin gets added when gram-positive coverage is needed. The reason is not the gut. The central venous lines that oncology patients carry bypass the normal skin barrier and are the dominant source of gram-positive bacteremia in this setting. Coverage for catheter-associated coagulase-negative staphylococci and methicillin-resistant Staphylococcus aureus is what vancomycin buys, and the indication is the line rather than the bowel.

13:32Nasogastric decompression is added in ileus or persistent vomiting. Granulocyte colony stimulating factor, filgrastim or pegfilgrastim, accelerates neutrophil recovery and is added for prolonged neutropenia. The mechanism that drives resolution is neutrophil recovery itself, because typhlitis exists because the host cannot contain translocating flora, and the durable answer is the return of containment. Antibiotics buy time. Neutrophil recovery closes the breach.

14:00Antimotility agents are avoided in active typhlitis. Slowing transit prolongs stagnation in a friable cecum and worsens distention in a wall that is already at risk of perforation.

14:12Empiric antifungal therapy is the fourth move and the most-tested escalation point. After seventy-two hours of persistent fever or sepsis despite optimal antibacterial coverage, empiric antifungal therapy is added, because invasive fungal infection becomes the dominant superinfection in prolonged neutropenia. Candida and Aspergillus are the most common organisms. Echinocandins such as caspofungin or micafungin, or liposomal amphotericin B, are the standard options. The seventy-two-hour window is the trigger. Persistent fever in a neutropenic patient on optimal antibacterial coverage is fungal until proven otherwise.

14:49That covers the conservative side of the algorithm. The next decision is when nonoperative management ends and surgery begins, and this is where the episode lands.

14:59Surgery is reserved for a short list of indications. Perforation. Refractory hemorrhage despite reversal of coagulopathy and thrombocytopenia. Full-thickness necrosis. Persistent sepsis despite optimal medical therapy. Intra-abdominal abscess that fails percutaneous drainage. The right hemicolectomy with ileostomy is the typical operation.

15:24The threshold for surgery is high for a reason. Neutropenia raises operative risk substantially. The patient cannot mount the wound healing or the perioperative infection control that ordinary surgical patients depend on. Most typhlitis patients respond to conservative therapy, and operating on a stable neutropenic patient adds risk without changing the trajectory. The threshold is high, but it is not infinite. Neutropenia raises operative risk but does not contraindicate life-saving resection. When the indication is perforation or uncontrolled hemorrhage, the operation is the only path forward, and the operative risk is accepted because the alternative is certain death from peritonitis or exsanguination.

16:04The recognition cues that move a typhlitis patient from conservative to surgical management are worth holding in mind. Hemodynamic deterioration despite resuscitation. New rebound or rigidity on exam. Rising lactate despite source control. New free intraperitoneal air on repeat imaging. New full-thickness pneumatosis or portal venous gas. Each of those is a signal that the cecum has perforated or is about to, or that ischemic injury has progressed beyond what antibiotics can salvage. Mortality in severe cases approaches fifty percent, and the patients who survive severe disease are the patients in whom the surgical decision was made at the right moment rather than too late.

16:45That closes neutropenic enterocolitis. The synthesis across both halves of this episode is the same logic. Identify the host state. The host state opens a tiered differential. The tier inside that differential predicts the pathogen or the entity, and the entity predicts the treatment. In HIV the tier is CD4 count and the entities are Cryptosporidium, microsporidia, cytomegalovirus, AIDS cholangiopathy, Kaposi sarcoma, and the post-treatment IRIS that follows immune reconstitution.

17:18In chemotherapy-related neutropenia the tier is absolute neutrophil count and the entity is typhlitis with its conservative-first algorithm and its narrow list of surgical indications. The framework is the same. The number tells you what to look for, and the entity tells you what to do.

17:36Episode three picks up the third major non-transplant setting, which is immune checkpoint inhibitor toxicity. We cover checkpoint inhibitor colitis and hepatitis along with the other immune-related adverse events. That includes pembrolizumab, nivolumab, and the combination CTLA-4 plus PD-1 regimen with its highest toxicity rate. We walk through the grade-based steroid-then-biologic management sequence with its seventy-two-hour escalation window. And we close on the irAE recognition framework that runs across organ systems and explains why the same patient often has thyroiditis, hypophysitis, and colitis at once.

18:17For the full chapter, the practice vignettes, and the topic-tagged question bank, head to board pearls dot com. You'll find the rest of the series on Apple Podcasts, Spotify, or wherever you listen to podcasts. That brings us to the end of episode three of four of chapter thirty four, and I'll see you in the next one.