Mechanisms of stool disorders and weight loss
The classification of the syndrome is based on the specific stage of digestion where the failure occurs. Changes can be either total (proteins, fats, and carbohydrates are not absorbed) or isolated (absorption of individual trace elements or bile acids is impaired).
Key mechanisms of symptom development:
- Diarrhea formation. If fats and fatty acids are not absorbed, the stool becomes loose, its volume increases sharply (causing polyfecalis), and an excess of neutral fat appears in the feces (steatorrhea). Bile acids contribute additionally: when their absorption is impaired, fluid is retained in the colon, further liquefying the feces.
- Wasting. Weight loss serves as the primary sign of energy component deficiency. The severity ranges from general weakness to terminal cachexia.
- Protein starvation. Decreased protein absorption logically leads to hypoalbuminemia. This results in a decrease in plasma oncotic pressure and the appearance of edema.
Systemic clinical manifestations
The clinical presentation of malabsorption is multifaceted. A patient may encounter either an isolated disorder (e.g., $B_{12}$-deficiency anemia alone) or a multisymptom failure.
Manifestations depend on which specific substances are no longer being absorbed:
- Calcium, magnesium, and vitamin D deficiency. Leads to bone pathology (demineralization, osteoporosis, osteomalacia). Patients complain of bone pain, and pathological fractures occur. Neuromuscular apparatus involvement manifests as tetany.
- Vitamin K deficiency. Disrupts hemostasis and provokes hemorrhagic diathesis, which may clinically present with melena and hematuria.
- Iron, folic acid, or vitamin $B_{12}$ deficiency. Naturally leads to the development of severe anemia syndrome.
- Polyhypovitaminosis. Affects the nervous system (neuropathies develop), skin, and mucous membranes. Typical signs include pellagra, glossitis, stomatitis, and oral ulcers.
Diagnostic workup
The diagnostic algorithm aims to confirm the fact of malabsorption itself and determine its cause.
- Coprological examination. The main goal is to detect steatorrhea (abnormally high neutral fat content).
- Biochemical blood test. Allows detection of decreased levels of albumin, cholesterol, prothrombin, as well as reduced concentrations of electrolytes (calcium, phosphorus, iron) and vitamins.
- Functional tests. The D-xylose test is widely used to verify malabsorption syndrome.
- Radioisotope diagnostics. Indicated when exudative enteropathy is suspected — a specific condition where protein loss through the GI tract wall exceeds the rate of hepatic synthesis. For confirmation, radioactively labeled chromium ($^{51}\text{Cr}$) albumin is administered intravenously.
- X-ray contrast study. Dilated loops of the small intestine are characteristic of celiac disease and scleroderma. If areas of induration or infiltration are detected, lymphoma, granulomatosis, or Whipple's disease is suspected.
- Morphological verification. Jejunal mucosal biopsy remains the primary method for definitively confirming conditions such as celiac disease, amyloidosis, Whipple's disease, and tropical sprue.
Briefly: answers to topical questions
What are the pathogenetic variants of malabsorption syndrome depending on the level of digestive tract involvement?
The classification of malabsorption syndrome is based on the stage of digestion where the failure occurs: the source indicates three levels of absorption impairment, but their specific names are not detailed.
Impairment may involve:
- absorption of all nutrients: proteins, fats, carbohydrates;
- absorption of individual components: vitamins, trace elements, bile acids.
What functional tests and assays are used to diagnose malabsorption syndrome?
For the diagnosis of malabsorption syndrome, the sources indicate the following functional and confirmatory methods:
- D-xylose test — used to verify malabsorption syndrome.
- Intravenous administration of radioactively labeled chromium ($^51\text{Cr}$) albumin — a method for confirming exudative enteropathy.
For diagnosing specific disorders associated with lactose intolerance, the sources also indicate:
- Lactose tolerance (glycemic) test — evaluation of blood glucose levels before and after an oral lactose load.
- Elimination trial with a lactose-free diet — resolution of clinical symptoms upon switching the patient to a lactose-free diet.
To remember the four main consequences of malabsorption, use the WABH rule: Weight loss, Anemia, hypovitaminosis (B, folate), Hypoproteinemia.
Class and exam questions
Why do edemas develop in malabsorption syndrome?
Due to insufficient protein absorption (or its loss in exudative enteropathy), blood albumin levels drop. This leads to a decrease in plasma oncotic pressure, causing fluid to freely escape into the tissues.
How are bile acids related to stool disorders?
If bile acids are not absorbed in the small intestine, they enter the colon, where they cause osmotic fluid retention. This contributes to profuse liquefaction of the feces.
Why is a jejunal biopsy performed?
Morphological examination is necessary for the precise diagnosis of specific conditions such as Whipple's disease, celiac disease, tropical sprue, and intestinal amyloidosis.
What else to study on this topic
- Mechanisms of exudative enteropathy and radioisotope diagnostics
- Differential diagnosis of hormone-induced diarrheas
- X-ray patterns of the small intestine in celiac disease and scleroderma
- Tropical sprue: the impact of climate and infections on the intestine
- Interpretation of the functional D-xylose test
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