Protein losing eneteropathy causes

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"protein-losing enteropathy" causes

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Protein-Losing Enteropathy (PLE) - Causes

Protein-losing enteropathy (PLE) refers to a group of GI and non-GI disorders characterized by hypoproteinemia and edema caused by excessive protein loss into the GI tract, in the absence of liver disease or renal proteinuria. The causes are classified into three main mechanistic groups:

1. Mucosal Ulceration (Exudation across damaged mucosa)

Protein loss results from direct mucosal breakdown and exudation:

Ulcerative colitis and Crohn's disease (inflammatory bowel disease)
Erosive gastritis / enteritis
Helicobacter pylori-associated gastritis
GI carcinomas (gastric, colorectal cancers)
GI lymphoma
Pseudomembranous enterocolitis (C. difficile)
Acute graft-versus-host disease

2. Non-ulcerated Mucosa with Altered Permeability

The mucosa is not frankly ulcerated but has increased epithelial permeability to proteins:

Celiac disease (gluten-sensitive enteropathy)
Ménétrier's disease (giant hypertrophic gastropathy) - large gastric folds, reduced acid secretion, protein loss from the stomach
Tropical sprue
Collagenous colitis
Eosinophilic gastroenteritis
Allergic/food-allergy enteritis
Whipple disease
Small bowel bacterial overgrowth
Viral enteritides (CMV, measles, varicella)
Parasitic infections: Giardiasis, Schistosomiasis, Strongyloides, Malaria
Bacterial infections: Salmonella, Shigella, Staphylococcal enteritis
Cystic fibrosis
Amyloidosis (secondary amyloidosis with intestinal ulcers from arteriole/lymphatic infiltration)
Connective tissue diseases: Systemic lupus erythematosus (SLE - can be the ONLY manifestation), Sjögren syndrome, mixed connective tissue disease, Henoch-Schonlein purpura, systemic sclerosis
Sarcoidosis
Tuberculosis (GI tuberculosis)
Neurofibromatosis (with mesenteric vascular changes)

3. Lymphatic Dysfunction / Obstruction (Increased interstitial/lymphatic pressure)

Increased lymphatic pressure causes protein-rich lymph to leak into the gut lumen. This group also causes steatorrhea (because chylomicrons exit via intestinal lymphatics):

Primary (Intrinsic) Lymphatic Disease:

Primary intestinal lymphangiectasia (congenital) - dilated, tortuous mucosal and submucosal lymphatics; presents before age 30 with edema, diarrhea, lymphocytopenia
Milroy's disease (primary peripheral lymphedema; ~50% also have intestinal lymphangiectasia)

Secondary Lymphatic Obstruction:

Lymphoma (mesenteric/retroperitoneal)
Tuberculosis (lymph node enlargement)
Sarcoidosis
Retroperitoneal fibrosis
Fibrosing mesenteritis

Cardiac / Circulatory Causes (Elevated central venous pressure -> backed-up lymphatics):

Fontan physiology (post-Fontan repair for congenital heart disease - now one of the most common causes as more patients reach adulthood)
Congestive heart failure
Constrictive pericarditis
Right-sided valvular disease
Chronic pericarditis

Summary Table

Category	Examples
Mucosal ulceration	IBD, GI cancers, pseudomembranous colitis, lymphoma, GvHD
Non-ulcerated mucosal disease	Celiac disease, Ménétrier's, eosinophilic gastroenteritis, infections (H. pylori, viral, parasitic), SLE, Whipple, cystic fibrosis
Lymphatic obstruction/dysfunction	Primary lymphangiectasia, lymphoma, TB, sarcoidosis, retroperitoneal fibrosis, Fontan physiology, CCF, constrictive pericarditis

Key Diagnostic Clue

Unlike nephrotic syndrome or liver disease, PLE causes loss of all serum proteins - both albumin AND globulins are low. Selective loss of albumin alone points toward renal/hepatic disease. Alpha-1 antitrypsin (AAT) fecal clearance is the diagnostic test of choice (AAT is resistant to intestinal proteolysis). Lymphopenia (loss of CD3+ T cells via lymphatics) is a marker when lymphatic obstruction is the mechanism.

Sources: Harrison's Principles of Internal Medicine 22E, p. 2592 | Yamada's Textbook of Gastroenterology, 7th ed., Box 61.2 | Goldman-Cecil Medicine | Tietz Textbook of Laboratory Medicine, 7th ed.

What are the diagnostic tests (alpha-1 antitrypsin, imaging) for PLE?

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Diagnostic Tests for Protein-Losing Enteropathy (PLE)

Step 1 - Initial Suspicion (Serum Tests)

Before specific tests, PLE is suspected when:

Low serum albumin AND low serum globulins (pan-hypoproteinemia) in the absence of liver disease, renal disease, or malnutrition
Selective loss of albumin alone points toward nephrotic syndrome or hepatic disease, NOT PLE
Selective loss of globulins alone suggests reduced synthesis, not PLE
Lymphopenia (particularly loss of CD3+ T cells) - a key clue when protein loss is from lymphatic obstruction, as lymphocytes are also lost via distended lymphatics

Step 2 - Confirmatory Tests for Enteric Protein Loss

A. Fecal Alpha-1 Antitrypsin (AAT) - The Preferred Clinical Test

Why AAT is ideal:

Constitutes ~4% of serum proteins; has a molecular weight similar to albumin
Resistant to degradation by gut proteases - survives intestinal transit intact
Not actively absorbed or secreted by the gut
Normally present in only low quantities in stool
Easy to assay

Test formats:

Test	Method	Notes
Spot stool AAT concentration	Single stool sample measured	Simple, useful screening tool; if elevated, is diagnostic - but NOT a reliable substitute for clearance
24-hour stool AAT	Stool collected over 24h	More representative than spot sample
AAT Clearance (most accurate)	= (Daily stool volume × stool AAT concentration) ÷ serum AAT concentration	Gold standard; directly quantifies daily protein loss

Interpretation:

AAT clearance elevated >3-fold above normal correlates with serum albumin <3.0 g/dL
When serum AAT is low (e.g., AAT deficiency, impaired hepatic synthesis), the test is invalid - must know the plasma AAT level before interpreting

Critical limitation: AAT is degraded at pH <3, so it cannot assess gastric protein loss (e.g., Ménétrier's disease). Acid suppression is required if gastroprotein-losing gastropathy is suspected (e.g., Zollinger-Ellison syndrome).

Causes of false elevation: Hematochezia, meconium, diarrhea (increased stool volume even in healthy persons), or ingestion of lactulose, sorbitol, or sodium sulfate.

B. Radiolabeled Protein Scintigraphy (Research/Specialized Use)

99mTc-labeled albumin or dextran scintigraphy - can detect and localize the site of protein loss
One retrospective study found scintigraphy more sensitive (100% vs 46%) and with higher negative predictive value (100% vs 63%) than AAT clearance in suspected PLE
131I-albumin, 51Cr-albumin, 51Cr-chloride - older radiolabeled methods, now largely replaced by AAT clearance in routine practice; useful research tools

Step 3 - Identifying the Underlying Cause

C. Endoscopy

Procedure	Use
Upper GI endoscopy (EGD)	Gastric disease (Ménétrier's), duodenal biopsy for celiac/Whipple
Colonoscopy	IBD, collagenous colitis
Video capsule endoscopy	Small bowel mucosal disease; detects ulcerations not reachable by standard endoscopy; requires confirming absence of strictures first
Double-balloon enteroscopy with biopsy	Most definitive - yields diagnosis in 88% of PLE patients; diagnoses 44% of cases missed by all other modalities
Peroral jejunal biopsy	Diagnosis of lymphangiectasia - shows dilated lymphatic lacteals (often patchy, so multiple specimens needed); endoscopy may show white opaque spots or white-tipped villi

Recommended endoscopic sequence (based on study of 25 PLE patients):

EGD + colonoscopy
Enteroclysis + video capsule endoscopy (after confirming no strictures)
Double-balloon enteroscopy with biopsy (if still undiagnosed)

D. Imaging

Modality	Use
CT of abdomen/pelvis	Detects mesenteric lymph nodes, lymphoma, retroperitoneal masses, bowel wall thickening, intestinal edema, lymphatic dilation; first-line cross-sectional imaging
MR enterography	Evaluates small bowel mucosa, detects intestinal/mesenteric edema and lymphatic dilation; less radiation than CT
Double-contrast small bowel radiography	May show thickened folds (from intestinal edema), nodular protrusions, absence of mucosal ulceration in lymphangiectasia
Lymphangiography (conventional)	Demonstrates malformed, hypoplastic lymphatics in congenital lymphangiectasia; less commonly used
Intranodal lymphangiography	Used in Fontan physiology to identify site of lymphatic leakage for therapeutic embolization
Noncontrast MR lymphangiography	Images central conducting lymphatics; differentiates PLE due to Fontan physiology from congenital lymphangiectasia - important distinction for management
Echocardiography / cardiac evaluation	Exclude constrictive pericarditis, right-sided valvular disease, Fontan physiology as cardiac causes

E. Biopsy (Histology)

Jejunal biopsy: dilated lacteals in lymphangiectasia; villous atrophy in celiac; PAS-positive macrophages in Whipple disease
Colonic biopsy: collagenous colitis, amyloid (Congo red stain)

F. Additional Tests for Nutritional Assessment

Stool fat quantification - assess malabsorption/steatorrhea (present in lymphatic obstruction)
Prothrombin time, serum calcium, serum carotene - fat-soluble vitamin deficiencies
Serum immunoglobulins - hypogammaglobulinemia if lymphatic loss is severe

Diagnostic Algorithm Summary

Hypoalbuminemia + edema
       ↓
Exclude: renal (urine protein), hepatic (LFTs), malnutrition
       ↓
Fecal AAT clearance (spot + serum AAT level)
  Elevated → confirms enteric protein loss
       ↓
Endoscopy (EGD + colonoscopy) + CT abdomen
       ↓
If inconclusive → Video capsule endoscopy
       ↓
If still inconclusive → Double-balloon enteroscopy with biopsy
       ↓
Lymphatic cause suspected → MR lymphangiography
Cardiac cause suspected → Echo + cardiac workup

Sources: Harrison's Principles of Internal Medicine 22E, p. 2592 | Yamada's Textbook of Gastroenterology, 7th ed. | Frameworks for Internal Medicine | Tietz Textbook of Laboratory Medicine, 7th ed. | Goldman-Cecil Medicine

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