Pediatric malabsorption syndrome

　　First, etiology

　　Any factor that can affect any link in the three periods (intraluminal phase, mucosal phase, and transport phase) of the digestion and absorption process of nutrients can cause malabsorption syndrome.

　　Second, pathogenesis

　　Disaccharide malabsorption is mainly due to the lack of specific disaccharidases in the small intestinal mucosa, which prevents the full hydrolysis of disaccharides in food into monosaccharides, affecting their absorption. It is also occasionally seen that monosaccharide absorption is impaired. Amylase is rare in deficiency except for newborns and generally does not cause clinical problems.

　　1. Primary disaccharide malabsorption

　　In primary disaccharide malabsorption, congenital lactase deficiency, sucrase-isomaltase deficiency, and glucose-galactose malabsorption are all autosomal recessive genetic diseases that are rare in clinical practice. In addition to the sucrase-isomaltase deficiency, which can become symptomatic after adding sucrose to the diet, the others become symptomatic soon after birth. The histology of small intestinal mucosal biopsy tissue is normal, while the activity of corresponding disaccharidases is reduced. In glucose-galactose malabsorption, the activity of disaccharidases is all normal. Malabsorption is due to the congenital deficiency of Na-glucose, Na-galactose carrier protein, and the child has good fructose absorption.

　　2. Secondary lactase deficiency and monosaccharide malabsorption

　　It is more common in clinical practice, as lactase is distributed at the top of the small intestinal villi. Any disease that can damage the intestinal mucosal epithelial cells and their brush border can lead to a deficiency in disaccharidases. Severe and widespread lesions can also affect the absorption of monosaccharides, such as acute enteritis (especially involving the upper small intestine, such as rotavirus enteritis, giardiasis, etc.), chronic diarrhea, protein-calorie malnutrition, immunodeficiency disease, celiac disease, and small intestinal surgery injury.

　　In the upper jejunum, lactase mainly exists in the apical brush border of the epithelial cells of the villi, sucrase is more abundant in the body of the villi, and maltase is widely distributed in the intestine with the highest content. Therefore, when the small intestine is damaged, lactase is most likely to be affected and takes the longest time to recover, which is the most common in clinical practice; maltase is least affected, and sucrase deficiency is rare and only causes a decrease in activity when the intestinal mucosa is severely damaged. At this time, the activity of lactase is often already affected, and it is often accompanied by malabsorption of monosaccharides.

　　3. Fat malabsorption

　　Fat malabsorption, also known as steatorrhea, is a syndrome caused by poor digestion and absorption of fats, which can be seen in various diseases such as pancreatic, liver, biliary, and intestinal diseases. Fat malabsorption caused by intestinal lesions often occurs simultaneously with malabsorption of other nutrients, known as malabsorption syndrome.

　　4. Protein malabsorption

　　Protein malabsorption is rare in clinical practice, usually occurring when the intestinal mucosa is widely damaged, often accompanied by malabsorption of fats. Protein malabsorption syndrome can also be accompanied by malabsorption of proteins. Protein loss from the intestinal mucosa can occur due to conditions such as lactose intolerance, celiac disease, giardiasis, inflammatory bowel disease, and intestinal lymphangiectasis. The presence of this protein in plasma can be confirmed by measuring α1-antitrypsin in feces, as it cannot be digested and hydrolyzed in the intestine. Therefore, when protein is渗出 from the intestinal mucosa, α1-antitrypsin can be detected in the feces.

　　Children with malabsorption syndrome of the intestines often have complications such as dehydration and acidosis, protein-calorie malnutrition, erythema buttocks, various vitamin and mineral deficiencies, anemia, etc., which seriously affect the healthy growth and development of children.

　　1. Manifestations directly caused by malabsorption

　　Weight loss, delayed growth and development, pale complexion, may have glossitis, abdominal distension and increased flatus, often accompanied by diarrhea. If it is fat malabsorption, the feces are light in color, soft, greasy and foamy, with a large amount and an unpleasant odor. This kind of feces is often sticky to the toilet, difficult to flush away. If there is an abrupt onset of diarrhea accompanied by abdominal distension and increased flatus after drinking milk, it often indicates that the child has a lactase deficiency.

　　2. Manifestations of various deficiencies secondary to malabsorption

　　The scope and severity of nutritional deficiency are related to the severity of the primary disease and the region and size of the gastrointestinal tract involved. Many patients with malabsorption have anemia, usually due to iron deficiency (microcytic anemia) and folic acid, vitamin B12 deficiency (megaloblastic anemia), which may cause neurological symptoms such as restlessness, insomnia, and irritability. There may be vitamin D and calcium deficiency, leading to convulsions, tetany, and delayed development of bones and teeth. Poor absorption of fat-soluble vitamin K can cause a decrease in prothrombin, leading to purpura and tendency to bleed. Deficiency of riboflavin can cause glossitis and cheilitis, and poor protein absorption can lead to hypoproteinemia edema, usually seen in the lower limbs.

　　3. Intestinal digestion and absorption disorders secondary to certain diseases

　　They may have different clinical manifestations of the primary diseases, such as jaundice in biliary obstruction, infection in gastrointestinal inflammation, and malabsorption caused by intestinal resection may have a history of surgery.

　　Since most cases are secondary malabsorption, the etiology is complex. The general preventive measures are to strengthen rational feeding, enhance physical fitness, prevent and treat various gastrointestinal diseases and malnutrition diseases, etc.

　　1. Screening test

　　1. Determination of fecal pH:The pH of fresh feces in children with poor glucose tolerance is often high.

　　2. Determination of reducing sugar in feces:Take 1 part of fresh feces, mix with 2 parts of water, and then centrifuge. Take 1ml of the supernatant liquid, add 1 tablet of Clinitest reagent, and obtain the concentration of reducing sugar by comparing the color with the standard card. ≥0.5g/dl is positive, and newborns >0.75g/dl are considered abnormal. The supernatant liquid can also be added with Benedict's liquid and heated to measure the reducing sugar.

　　Since sucrose is not a reducing sugar, 1 part of feces needs to be mixed with 2 parts of 1N HCl, heated, and the supernatant liquid taken out. At this point, sucrose has been hydrolyzed into monosaccharides and can be measured for reducing sugar by the aforementioned method. Since the unabsorbed sucrose is often decomposed into reducing sugar by bacteria in the colon, it is usually not necessary to add HCl for hydrolysis first. However, after acid treatment, the fecal sugar is significantly higher than that without treatment, indicating malabsorption of sucrose in the child.

　　The presence of other reducing substances in the stool, such as vitamin C, can present false positives.

　　II. Sugar-Breath Test

　　The method is sensitive, reliable, simple, and non-invasive, but it requires a gas chromatograph to measure the hydrogen content in the exhaled breath. Humans themselves do not produce hydrogen, and the hydrogen in the exhaled breath is produced by the fermentation of sugar in the colon by bacteria. Most absorbable sugars can be completely absorbed before reaching the colon in normal people. The fermentation and metabolism of unabsorbed sugars by intestinal bacteria are the only source of hydrogen in human exhaled breath. Utilizing this principle, malabsorption of sugars by the small intestine can be measured.

　　Before and after consuming a certain test sugar, measure the hydrogen or 14CO2 in the exhaled breath. After consuming the test sugar, if the exhaled hydrogen increases or the exhaled 14CO2 decreases, it indicates malabsorption of the test sugar. After fasting for 8 to 12 hours at night, measure the exhaled hydrogen as a baseline, then take 2g/kg of the sugar to be tested orally, not exceeding 50g. Some advocate reducing the dose to 0.25 to 0.5g/kg to reduce the induction of symptoms of sugar intolerance. Collect the exhaled hydrogen content every half hour for a total of 2 to 3 hours. If the total hydrogen content exceeds 20×10-6ppm of the baseline value, it can be diagnosed as malabsorption of the tested sugar. Antibiotics can suppress intestinal bacteria in children, which may result in false negatives.

　　III. Small Intestinal Mucosal Biopsy

　　It is possible to obtain thin slices of intestinal mucosa by endoscopy or through the oral insertion of a Crosby intestinal biopsy catheter, and then perform histological examination and directly determine the content of various disaccharidases. This is particularly beneficial for the diagnosis of congenital sugar malabsorption.

　　IV. Dextrose Absorption Test

　　Under normal renal function, the excretion amount of xylose in urine can reflect the absorption function of the small intestine. The positive rate of this test for diagnosing malabsorption caused by general damage to the small intestinal mucosa is over 70%; for pancreatic diseases and diseases that only involve the ileum, the xylose test is positive; for patients with renal insufficiency or delayed gastric emptying, false positives may occur. Method: Take 5g of dextrose (dissolved in 250ml of water) on an empty stomach, then drink 200 to 300ml of water, collect urine for 5 hours, and determine the xylose content in the urine. The normal value is (1.51±0.21)g. If the excretion amount is 1 to 1.16g, it is可疑.

　　V. Vitamin B12 Absorption Test

　　First, intramuscular injection of vitamin B12 1.2mg to saturate the body's inventory, then take 60Co (cobalt) or 57Co-labeled vitamin B12 22μg orally, collect 24 hours of urine, and determine the radioactive content in the urine. The normal excretion amount of the radioactive substance through urine should be greater than 8% to 10% of the oral dose. A value lower than this indicates malabsorption, which is common in malabsorption at the end of the ileum or after resection, excessive proliferation of intestinal bacteria (such as blind loop syndrome), and pernicious anemia caused by a lack of intrinsic factor.

　　1. Apple Diet

　　Apples contain tannins and have astringent effects. Wash an apple, steam it, and eat the flesh or mash it without the peel for consumption. The dosage is 30 to 60 grams per time, three times a day. Apple soup is also an auxiliary beverage for treating diarrhea. Cut the apple into pieces, add 250 milliliters of water and a small amount of salt, and you can also add 5% sugar. Boil the mixture as a tea substitute, suitable for infants under 1 year old.

　　2. Yolk Diet

　　Boil the eggs, peel off the shells and yolks, melt the yolks in the pot over low heat to extract oil, 1 egg yolk oil per day for infants under 1 year old, taken 2-3 times a day, 3 days as a course of treatment, for the treatment of diarrhea, and has the effect of invigorating the spleen and stomach and stopping diarrhea; the egg cake steamed with a little flour and ginger slices also has the same effect.

　　3. Chestnut Paste Diet

　　Use 3-5 chestnuts, peel and crush them, boil them in water to make a paste, add sugar for seasoning and eat, 2-3 times a day, with the effect of warming and stopping diarrhea.

　　I. Treatment

　　Treatment Principle: Targeted etiological treatment, correction of nutritional deficiency, and use of necessary metabolic therapy.

　　1. Etiological Treatment

　　(1) Discontinuation of intolerant diet: For example, stop eating foods containing lactose for those with lactose malabsorption.

　　(2) Supplementation of deficient digestive enzymes: For example, lactase for lactose malabsorption, and pancreatin for incomplete pancreatic function.

　　(3) Chronic enteritis caused by bacterial infection can be treated with antibiotics according to circumstances, and microecological preparations can also be used appropriately. After the cause is removed, the symptoms of most patients can be relieved.

　　2. Nutritional Therapy

　　Principally, high-calorie, high-protein, low-fat foods should be used. Severe cases often have anorexia and poor digestion and absorption function, and the food and drugs ingested are often excreted intact in the feces. At this time, parenteral nutrition can be used first, and after the symptoms improve, it can be changed to elemental diet oral administration, that is, using easily digestible or semi-digested food. For example, fat can be used with medium-chain triglycerides, sugar with maltodextrin or glucose, and protein with hydrolyzed protein or amino acids. Eat in small amounts and more frequently, gradually increasing, step by step. Currently, there are milk-free infant formula and hydrolyzed protein elemental diets.

　　3. Symptomatic Treatment

　　(1) Supplementation of necessary vitamins, inorganic salts, and trace elements.

　　(2) Timely correction of water, electrolyte, and acid-base imbalance: In theory, the treatment is simple, as long as intolerant disaccharides or monosaccharides are removed from the diet, it can be effective, but there are many specific difficulties in actual implementation, such as how to find a diet that meets the requirements, how to maintain calories after restricting sugar, and how much sugar restriction can keep the child asymptomatic.

　　II. Prognosis

　　Commonly die due to secondary infection or water and electrolyte imbalance leading to organ failure.