Má absorção gastrointestinal

What is gastrointestinal malabsorption?

Gastrointestinal malabsorption is a failure to fully absorb nutrients from the gastrointestinal tract. The digestion and absorption of nutrients within the gastrointestinal tract requires a complex interaction between motor, secretory, digestive and absorptive processes that are vulnerable to various potential disturbances which may lead to global or specific malabsorption syndromes.¹

The outcome is malnutrition. Malnutrition may also be caused by inadequate diet with or without malabsorption. See also the separate Desnutrição artigo.

Clinical featuresof gastrointestinal malabsorption^{2 3}

Malabsorption, from whatever cause, may be accompanied by:

• Changes in weight and growth:
  

  • Inadequate absorption of calories will lead to unintentional weight loss in adults or faltering growth in children.

• Gastrointestinal symptoms:
  

  • Diarreia crônica is common. Chronic diarrhoea may be defined as the abnormal passage of three or more loose or liquid stools per day for more than four weeks and/or a daily stool weight greater than 200 g/day.

  • Steatorrhoea is often present. There is excessive fat in the stools and they become pale, bulky and offensive in smell. Stools float and are difficult to flush away. They often leave a greasy rim around the pan.

• Histórico familiar:
  

  • Some diseases associated with malabsorption are found more frequently in families - eg, doença celíaca, Doença de Crohn, fibrose cística e disaccharidase deficiencies (lactase). It is therefore important to explore the family history carefully.

• Signs of deficiencies may be apparent. There may be:
  

  • Deficiência de ferro sem anemia.

  • artigo sobre anemia por deficiência de ferro.

  • Deficiência de folato ou deficiência de vitamina B12.

  • Bleeding, resulting from low vitamin K.

  • Edema, which occurs in protein/calorie malnutrition.

There may also be clinical features associated with the particular cause of malabsorption. The most common causes in the UK are doença celíaca, Doença de Crohn e pancreatite crônica.

However the malabsorption of simple carbohydrates is the most common type of non-immune-mediated food intolerance, affecting 20-30% of the European population⁴ .

Various causes of gastrointestinal malabsorption^{2 5}

Mucosal causes

• Doença celíaca usually presents in childhood but can present later.

• Intolerância à lactose.

• Alergia à proteína do leite de vaca.

• Soya milk intolerance.

• Fructose intolerance and malabsorption: simultaneous consumption of glucose reduces fructose malabsorption⁶ .

• Infecção:
  

  • Giardíase.

  • Doença de Whipple.

  • Intestinal tuberculosis.

  • Espru tropical.

  • Diarreia do viajante.

  • Diphyllobothriasis (tapeworm can cause vitamin B12 malabsorption).

  • Ancylostomiasis (hookworm).

  • Estrongiloidíase (nematode).

• In patients with an inflammatory bowel disorder and malabsorption, an immune deficiency, including HIV enteropathy, should be considered.^{7 8}

• Intestinal lymphangiectasia and other causes of lymphatic obstruction include lymphoma, tuberculose and cardiac disease.

Intraluminal causes

• Pancreatic insufficiency:⁹
  

  • Fibrose cística

  • Pancreatite crônica

  • Carcinoma of pancreas

  • Síndrome de Zollinger-Ellison

• Bile acid malabsorption: defective secretions of bile salts, due to cholestatic jaundice or disease of the terminal ileum.

• Small intestinal bacterial overgrowth (SIBO).¹⁰

Structural causes

• Intestinal hurry:
  

  • Post-gastrectomy

  • Post-vagotomy

  • Gastrojejunostomy

• A blind loop syndrome involves disturbance of normal gut flora with malabsorption.

• Fistulae.

• Diverticulae and strictures.

• Doença de Crohn.

• Amiloidose.

• Síndrome do intestino curto.

• Eosinophilic gastroenteropathy.

• Mesenteric arterial insufficiency.

• Enterite por radiação.

Causes outside the gut

• Hipertireoidismo.

• Hipotireoidismo.

• doença de Addison.

• Diabetes mellitus.

• Hiperparatireoidismo.

• Hipoparatireoidismo.

• Síndrome carcinoide.

• Widespread skin disease (rapid cell turnover may also affect gut mucosa).

• Collagen diseases.

• Transtornos alimentares.

• Factitious diarrhoea due to purgative abuse.

Investigações^{3 5 11}

Exames de sangue

• Hemograma completo.

• Plasma viscosity, ESR, CRP.

• Vitamin B12 level.

• Red cell folate.

• Iron status (usually ferritin but can be iron and iron-binding capacity).

• Clotting screen for vitamin K deficiency.

• Serum albumin.

• Calcium (corrected for albumin level).

• Magnesium, zinc, phosphorous.

• Vitamin D.

• Anti-endomysial, anti-reticulin and alpha-gliadin antibodies (coeliac screen).

• Testes de função hepática.

Stool

• Faecal microbiological assessments may be indicated.

• Sudan stain for fat globules.

• Tests for secretory function - eg, elastase or chymotrypsin in stool.

Imaging and endoscopy

• Abdominal ultrasound (gallbladder, liver, pancreas, intestinal wall, adenopathy).

• Barium follow-through may show structural abnormalities.

• Jejunal biopsy (and aspirate for possibility of SIBO).

• Ileocolonoscopy including biopsies of colon and ileum.

• CT; MRI of pancreatic duct-systems or endoscopic retrograde cholangiopancreatography (ERCP).

Breath hydrogen tests

Take samples of end-expired air; give glucose; take more samples at half-hourly intervals. If there is bacterial overgrowth there is an increase in exhaled hydrogen one hour after ingestion.

Gastrointestinal malabsorption treatment and management^{2 3 5}

Nutritional support may be required for malabsorption.

Management otherwise depends upon the cause. For example:

• Coeliac disease requires a strict gluten-free diet.

• Pancreatic insufficiency requires the oral administration of enzymes with food.

• Blockage of the flow of bile requires surgery.

• Crohn's disease usually responds to steroids.

• Blind loop syndromes may require further surgery.

• Where bile salts are not reabsorbed, it may be necessary to give resins to bind them.¹²

• If there is folate deficiency and possibly B12 deficiency too, it is imperative to give an injection of vitamin B12 before starting folate supplementation. Otherwise, there is a risk of precipitating subacute combined degeneration of the cord.
  

Malabsorption complications

Complications are related to the underlying disease.

• Lassitude is common. Children will have stunted growth.

• Untreated coeliac disease may result in small bowel adenocarcinoma or lymphoma.

• Infertility is common, especially in coeliac disease.

• Anaemia may occur.

• Raquitismo, osteomalacia ou osteoporose podem ocorrer.