Despite the distinct underlying pathological mechanisms of malabsorption and maldigestion, the term malabsorption is used to refer to both disorders in clinical practice. Malabsorption (e.g., celiac disease, lactose intolerance) describes a malfunction of the intestinal wall, resulting in the insufficient absorption of breakdown products. Maldigestion (e.g., exocrine pancreas insufficiency or cholestasis) is caused by an intraluminal disorder (insufficient secretion of pancreatic enzymes or bile), which prevents the adequate breakdown of food in the intestinal lumen. Both disorders can lead to malnourishment, which, in children, may manifest with delayed and inadequate physical development. Adults mainly present with chronic diarrhea, weight loss, and signs of malnutrition (e.g., iron deficiency anemia). Diagnostic tests assess the digestion of individual food components. Management focuses on the underlying disease; e.g., patients with celiac disease should adhere to a gluten-free diet.
Malabsorption disorders can be caused by either the insufficient absorption or digestion of nutrients. The condition can be further defined as global or partial.
- Global malabsorption: in diseases causing diffuse mucosal damage or a reduction of the absorptive surface (e.g., celiac disease)
- Partial malabsorption: caused by a localized absorption impairment, resulting in deficiencies of specific nutrients (e.g., vitamin B12 deficiency in patients with diseases affecting the terminal ileum)
Maldigestion is an impaired breakdown of food in the intestinal lumen.
Exocrine pancreatic insufficiency
- Definition: inability of the pancreas to produce enzymes necessary for digestion, including amylase, lipases, and proteases (e.g., trypsinogen, chymotrypsinogen, elastase)
- Pathophysiology: : lack of digestive enzymes → malabsorption of carbohydrates, proteins, fats, fat-soluble vitamins (A, D, E, K), and vitamin B12
- Clinical features: steatorrhea, deficiency symptoms
- Gastric resection: lack of gastric acid → impaired breakdown of nutrients
- Bile acid deficiency: : e.g., cholestasis, bile acid malabsorption → incomplete emulsification of fats
- Mechanism of action: Reversibly inhibits gastric and pancreatic lipase, resulting in a decrease in fat breakdown and absorption
- Indication: weight loss in obese patients
- Recommendation: should be taken with meals containing fat
- Side effects: numerous gastrointestinal side effects
Malabsorption is an impaired absorption of digested food caused by alterations of the intestinal mucosa.
- Inflammatory bowel disease (e.g., Crohn's disease)
- Celiac disease ()
- Infections (e.g.,tropical sprue; , giardiasis, traveler's diarrhea, Whipple's disease)
- Lactose intolerance
- Small intestine resection (short bowel syndrome)
- Chronic mesenteric ischemia
- Radiation colitis
- Impaired intestinal lymphatic circulation
- Hormonally active tumors (gastrinoma, VIPoma, carcinoid tumors)
- Small intestinal bacterial overgrowth (SIBO; )
- HIV enteropathy
- Global malabsorption
- Partial (isolated) malabsorption: only symptoms specific to individual nutrient deficiencies (e.g., impaired cobalamin absorption with megaloblastic anemia)
- Deficiency of : See “Vitamin A deficiency” and “Vitamin D deficiency” in “Osteomalacia and rickets”
- Deficiency of : See symptoms of individual vitamin deficiencies in “Vitamins”.
- Clinical findings: immune dysfunction, impaired wound healing, hypogonadism, diarrhea, dermatitis, alopecia, abnormal taste and smell
- Diagnosis: measurement of plasma zinc levels
- Treatment: oral zinc supplementation
- Other deficiencies
- Blood tests: macrocytic and/or microcytic ; ↓ electrolytes, ↓ total protein, vitamin deficiencies
- Analysis of fecal fat; over 72 hours (e.g., using Sudan stain)
- Detection of pathogens
D-xylose absorption test: assesses the absorptive function of the upper small intestine
- Method: The patient fasts overnight, then 25 g of D-xylose is administered orally. Then:
- Hydrogen breath test: assess the intestinal absorption of individual carbohydrates
- Further testing (for underlying diseases): e.g., or
Clinical features: hypoalbuminemia with peripheral edema
- In cases of systemic diseases, symptoms may be those of the underlying condition.
- Further gastrointestinal symptoms may occur depending on the underlying disorder.
- Treatment: treatment of the underlying disease
The differential diagnoses listed here are not exhaustive.