A recent post on the pediatric GI listserv (GI Bulletin Board) this past month discussed protracted diarrhea of infancy.  The posting noted that this was a frequent problem that would hospitalize infants (in the first 6 months of life) for weeks & often would require parenteral nutrition.   “The cause of protracted diarrhea of infancy is usually ill-defined and is characterized by chronic nutritional failure, septic complications, and a high mortality.” ( Am J Dis Child 1973:125:358-364).  The availability of elemental diets have made this problem quite infrequent.  These infants often improve quickly, even with severe diarrhea.

Congenital diarrhea, rather than acquired diarrhea, remains much more of a challenge.  However, our understanding has improved a great deal in the past two decades.  My approach in this area relies a lot on the teachings I received as a fellow and from articles in the literature, especially the work of Dr. Martín.

For congenital diarrhea, my approach & differential diagnosis  are as noted below:

1. Measure inputs/outputs for carefully –may need to use rectal ‘ng tube’ to assess stool output.  Check stool electrolytes.  Careful IVFs needed.

2. Trial of neocate (contains glucose polymer) excludes congenital lactase deficiency/most disaccharidase deficiencies.

3. Trial of RCF excludes glucose-galactose malabsorption.

4. The, remaining cases are considered protracted diarrhea of infancy (PDI):

• PDI with normal villi: consider congenital chloride diarrhea, congenital sodium, sodium co-transporter deficiencies, heparan sulphate deficiency, glycosylation defect, neurogenin-3, congenital short gut.
• PDI with abnormal villii/villous atrophy: post-infectious, autoimmune/allergic enteropathies, IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked).  If villous atrophy w/o inflammation, consider microvillus inclusion disease and tufting enteropathy.

1-Microvillus inclusion disease- An experienced pathologist should be able to establish this diagnosis with EM.

2-Congenital Na diarrhea –  these patients have a high volume secretory diarrhea that is very alkaline and contains high concentrations of the Na+.

3-Congenital disorder of glycosylation- in the absence of PLE, this should be taken off the list.

4-Glucose-galactose malabsorption-  all the GGM patients should have (at least at some point) +4 clinitest.   An RCF (Ross Carbohydrate Free) trial is a wonderful screen for GGM as the stool output will go to the normal range without carbohydrates.  It should be noted that sucrase-isomaltase deficiency improves with RCF as well.

5-Congenital enterokinase deficiency- if the child’s diarrhea persists while
on Neocate, you have essentially ruled out this disorder.

6-Autoimmune enteropathy -consider if the diarrhea is secretory
in nature; look specifically at the intraepithelial (normal in IPEX), lamina propria (increased number of CD8 and CD4 in IPEX) lymphocytes. IPEX is also associated with increased mucosal eosinophils. Also, serum IgE level is usually very high in IPEX patients. If there is  any evidence of glucose intolerance, check for anti-islet cell antibodies.

7-Ileal bile acid receptor defect- The diarrhea is generally in character
and is exacerbated with addition of dietary fats. The diarrhea should
improve with a trial of cholestyramine and a low fat diet.  Bile acid
absorption by the ileum may be measured using the bile acid analogue
75Se-homocholic acid-taurine test. (give a trial of cholestyramine if
75Se-homocholic acid-taurine testing is not available.)

8- Congenital chloride diarrhea (CCD)- Probably the most common congenital
diarrhea-these patients generally have fecal chloride concentrations that
exceeds the concentration of cations (Na+ and K+).

9- Chylomicron retention disease- You can certainly rule this out by H&E as
enterocytes are laden with fat.  However, this can be missed this if patient is fasted for a prolonged period of time before the biopsy was taken.  Interestingly, unlike all other enterocyte specific congenital diarrhea, this disorder will be accompanied by carbohydrate and AA malabsorption while on a fat containing enteral diet.

10. Mutant neurogenin-3- check immunostains on the small intestinal, colonic biopsies for chromogranin A to see if there is a paucity or agenesis of the enterochromaffin cells.  At UCLA, they are actively performing DNA sequencing for this disorder and can have results within a week. If this is needed, contact Dr. Martín & he can send a copy of the UCLA approved IRB form and a kit to isolate DNA from saliva.