Diagnosis

Lactose intolerance

Etiology

Cause [aas][jue][4mk]

• Primary lactase deficiency: production declines over time (the most common type)

• Secondary lactase deficiency: due to injury to the small intestine (infection, disease)

  • Infections: Gastroenteritis, Giardiasis, Ascariasis

  • Inflammation: Crohn disease, Celiac sprue, Tropical sprue

  • Other: Gastrinoma, Radiation enteritis, Diabetic gastropathy, Carcinoid syndrome, Whipple syndrome, HIV enteropathy, Kwashiorkor, Chemotherapy, Antibiotics

• Developmental lactase deficiency: prematurely born infants

• Congenital lactase deficiency: an extremely rare genetic disorder in which the small intestine produces little or no lactase enzyme from birth [aas]

Pathophysiology

1. Lactose (a disaccharide found in milk) is hydrolyzed into glucose and galactose by the enzyme lactase, located in the small intestinal border.

2. The lactase enzyme levels are the highest shortly after birth and decline with aging

3. Asian, South American, and African populations commonly have lactose intolerance while people from the northern Europe or the northwestern Indian subcontinent are likely to retain the ability to absorb lactose into adulthood [jue]

4. The osmotic load of the unabsorbed lactose causes:

   • Secretion of fluid and electrolytes

   • Acceleration of small intestinal transit

   • Maldigestion and fermentation of free lactose by colonic bacteria to yield short-chain fatty acids and hydrogen gas.

5. This causes loose stools, abdominal bloating and pain, flatulence, nausea, borborygmi, and diarrhea [jue][grq]

Complications [4mk]

• Osteopenia

• Osteoporosis

• Malnutrition

• Weight loss

• Rickets

• Growth failure

Epidemiology

Incidence per 100.000 [4mk][grq][aas]

Approach

• Milk tolerance test: [4mk]

  • Administer 500 mL of milk and measure the blood glucose level

  • An increase of less than 9 mg/dL indicates lactose malabsorption

• Hydrogen breath test: post-lactose hydrogen value rises >20 ppm

• Stool acidity test: Unabsorbed lactose is fermented by colonic bacteria into lactic acid

• Dietary elimination

• Lactose tolerance test: Blood glucose levels after giving an oral lactose load

• Small bowel biopsy

• Genotyping

Treatment

Primary lactase deficiency/Lactose intolerance is not lethal: [jue]

1. Dietary adjustment:

   • Soy-based milk, yogurt and fermented products (cheeses) are better tolerated

2. Probiotics

3. Lactase enzyme pills

Differential diagnoses

Celiac disease, Crohn disease, Cystic fibrosis, Diverticulitis, Gastrinoma, Gastroenteritis, Giardiasis, Irritable bowel syndrome, Tropical sprue, Ulcerative colitis