Protein-Losing Enteropathy (PLE) from Enteroinvasive Intestinal Infections

Definition and Pathophysiologic Framework

Specific Pathogens Causing Enteroinvasive PLE

1. Bacterial Infections

• Acute salmonellosis has been directly documented to produce PLGE.
• Invasive strains penetrate the ileal and colonic mucosa, causing inflammation and ulceration with direct protein exudation.

• One of the best-documented bacterial causes of PLGE. The degree of protein loss is species- and strain-dependent: Shigella dysenteriae type 1 causes significantly greater enteric protein loss than other strains.
• The mechanism is mucosal invasion with ulcerative colitis-like destruction.

• Both symptomatic infection and asymptomatic colonization can lead to PLGE.
• In a study of elderly nursing home patients: PLGE was found in all 12 patients with pseudomembranous colitis, 6/14 with C. difficile diarrhea without pseudomembranes, and 6/12 with asymptomatic colonization. However, a subsequent prospective case-control study found PLGE only in symptomatic infection (19/20 patients), not asymptomatic colonization (0/10 patients).
• Mechanism: toxin-mediated mucosal disruption and frank pseudomembrane formation.

• Listed among ulcerative causes of PLGE in Yamada's classification (Box 61.2), via erosive gastritis.

• Bacterial toxins and products directly injure the epithelial barrier, enhancing intestinal permeability.
• In severe cases this leads to frank PLE, with loss of brush border enzymes, impaired absorption, and systemic inflammatory cytokine release (TNF-alpha).
• Luminal protein consumption by the overgrown bacteria contributes further to hypoproteinemia.

• Causes PLE through two routes: (1) ulcerative intestinal disease from mucosal invasion, and (2) mesenteric lymph node enlargement/fibrosis that obstructs lymphatic flow.
• Mesenteric tuberculosis can produce retroperitoneal lymph node enlargement or fibrosis, impeding lymphatic egress from intestinal walls.

• Causes PLE via mechanical obstruction of intestinal lymphatic vessels and increased hydrodynamic pressure in lymphatics.
• Manifests with diarrhea, steatorrhea, lymphocytopenia, and hypoproteinemia.

2. Parasitic Infections

• Documented to produce PLGE through non-ulcerative mucosal damage. The trophozoites attach to the brush border, disrupting absorptive surface and altering epithelial permeability.

• Directly documented to cause PLGE. Larvae invade intestinal mucosa; in hyperinfection syndrome, massive mucosal destruction can produce severe protein losses.

• Causes PLGE both through intestinal mucosal inflammation and through mesenteric/portal venous hypertension causing secondary lymphatic obstruction and increased hydrostatic pressure.

• In heavy infections, intestinal obstruction, PLE, malabsorption, impaired vitamin B12 absorption, hypoalbuminemia, and anasarca can occur. The adult worms cause traumatic, toxic, and obstructive damage to duodenal and jejunal mucosa.
• >50 species of intestinal trematodes in the Far East, Middle East, and North Africa have been linked to human disease.

• A severe form of PLE-causing parasitic infection. Adult worms migrate to mucosal crypts of the small intestine, deposit larvae (autoinfection), leading to overwhelming infection. Clinical disease: severe diarrhea, anorexia, vomiting, protein-losing enteropathy with malabsorption and anasarca.

• Listed among non-ulcerative causes of PLGE (Yamada Box 61.2), likely via systemic inflammatory mechanisms affecting gut permeability.

3. Viral Infections

Pathophysiology: Why Infections Cause Protein Loss

Enteroinvasive organism
        |
   Mucosal invasion / toxin elaboration
        |
   ┌────────────────────────────────────────────┐
   │  Ulcerative pathway     Nonulcerative pathway  │
   │  - Physical destruction  - Altered epithelial  │
   │    of mucosal barrier      permeability        │
   │  - Direct exudation of  - Loss of brush border │
   │    plasma proteins         enzymes             │
   │  - Shigella, Salmonella,- SIBO, Giardia,       │
   │    C. difficile, TB        viral enteritis     │
   └────────────────────────────────────────────┘
        |                         |
        └──────────┬──────────────┘
                   |
        Lymphatic obstruction (TB, Whipple's, Schistosoma)
                   |
        Loss of albumin, IgM, IgG, IgA, fibrinogen,
        ceruloplasmin, α1-antitrypsin into gut lumen
                   |
        Hypoproteinemia → Reduced plasma oncotic pressure
                   |
        Peripheral edema, ascites, lymphocytopenia

Clinical Features

• Dependent pitting edema (from reduced plasma oncotic pressure)
• Diarrhea (may be bloody in ulcerative forms)
• Hypoalbuminemia - pan-protein loss (albumin, IgG, IgM, fibrinogen)
• Lymphocytopenia - when lymphatic obstruction is the mechanism (loss of CD3+ T cells)
• Steatorrhea - when lymphatic dysfunction impairs chylomicron transport
• Fat-soluble vitamin deficiencies (A, D, E, K) with lymphatic disease

Diagnosis

Treatment Principles

• Antibiotics targeted to the causative organism (e.g., metronidazole for Giardia/amoebiasis, anti-TB regimen for intestinal TB, vancomycin/fidaxomicin for C. difficile)
• Antiparasitic therapy (e.g., ivermectin for Strongyloides, praziquantel for schistosomiasis/flukes)
• Nutritional support: high-protein diet, albumin infusions in severe cases
• MCT (medium-chain triglyceride) supplementation in lymphatic disease - MCTs bypass lymphatics, absorbing directly into portal blood

Summary Box: Infectious Causes of PLE by Mechanism

• Harrison's Principles of Internal Medicine, 22nd Ed. (2025), Chapter 336, p. 2592
• Yamada's Textbook of Gastroenterology, 7th Ed., Chapter 61 (PLGE section, Box 61.2)
• Goldman-Cecil Medicine, International Ed., p. 1476
• Yamada's Textbook of Gastroenterology, 7th Ed., Chapter 58 (SIBO, Table 58.2)