Protein-losing enteropathy comprises a number of conditions that result in excessive loss of serum proteins into the GI tract.
The normal intact gut epithelium prevents the loss of serum proteins. Proteins may be lost through one of three mechanisms: (1) mucosal disease with ulceration, resulting in the loss of proteins across the disrupted mucosal surface, such as in chronic gastric ulcer, gastric carcinoma, or inflammatory bowel disease; (2) lymphatic obstruction, resulting in the loss of protein-rich chylous fluid from mucosal lacteals, such as in primary intestinal lymphangiectasia, constrictive pericarditis or heart failure, Whipple disease or tuberculosis, Kaposi sarcoma or lymphoma, retroperitoneal fibrosis, or sarcoidosis; and (3) idiopathic change in permeability of mucosal capillaries and conductance of interstitium, resulting in "weeping" of protein-rich fluid from the mucosal surface, such as in Ménétrier disease, Zollinger-Ellison syndrome, viral or eosinophilic gastroenteritis, celiac disease, giardiasis or hookworm, common variable immunodeficiency, SLE, amyloidosis, or allergic protein-losing enteropathy.
Hypoalbuminemia is the sine qua non of protein-losing enteropathy. However, other serum proteins such as alpha-1-antitrypsin also are lost from the gut epithelium. In protein-losing enteropathy caused by lymphatic obstruction, loss of lymphatic fluid commonly results in lymphocytopenia (less than 1000/mcL), hypoglobulinemia, and hypocholesterolemia.
In most cases, protein-losing enteropathy is recognized as a sequela of a known GI disorder. In patients in whom the cause is unclear, evaluation is indicated and is guided by the clinical suspicion. Protein-losing enteropathy must be distinguished from other causes of hypoalbuminemia, which include liver disease and nephrotic syndrome, and from heart failure. Protein-losing enteropathy is confirmed by determining the gut alpha-1-antitrypsin clearance (24-hour volume of feces × stool concentration of alpha-1-antitrypsin ÷ serum alpha-1-antitrypsin concentration). A clearance of more than 27 mL/24 hours is abnormal.
Laboratory evaluation of protein-losing enteropathy includes serum protein electrophoresis, lymphocyte count, and serum cholesterol to look for evidence of lymphatic obstruction. Serum ANA and C3 levels are useful to screen for autoimmune disorders. Stool samples should be examined for ova and parasites. Evidence of malabsorption is evaluated by means of a stool qualitative fecal fat determination. Intestinal imaging is performed with small bowel enteroscopy, CT enterography, or wireless capsule endoscopy of the small intestine. Colonic diseases are excluded with colonoscopy. CT of the abdomen is performed to look for evidence of neoplasms or lymphatic obstruction. Rarely, lymphangiography is helpful. In some situations, laparotomy with full-thickness intestinal biopsy is required to establish a diagnosis.
Treatment is directed at the underlying cause. Patients with lymphatic obstruction benefit from low-fat diets supplemented with medium-chain triglycerides. Case reports suggest that octreotide may lead to symptomatic and nutritional improvement in some patients.
et al. Protein-losing enteropathy. Curr Opin Gastroenterol. 2020;36:238.
et al. Protein-losing enteropathy and primary intestinal lymphangiectasia. QJM. 2020;113:224.