Diarrhea, abdominal pain, and flatulence following ingestion of milk or products containing milk are common complaints in pediatric practices. The pediatrician needs to be aware of the management of lactose intolerance to help guide a reasonable workup and plan. Additionally, parental decisions about intake and avoidance of milk products impact not only the calcium and vitamin D intake of children but also other dietary choices such as intake of protein fat.
Pathophysiology of lactose intolerance
It is important for the pediatrician to understand the clinical spectrum of lactose problems.1,2 Generally, the syndrome incidence is lower in younger children and begins to increase around school age. The following definitions are important for the pediatrician to understand:2
· Lactase deficiency—decreased lactase enzyme activity in the intestinal brush border.
· Lactose malabsorption—failure to absorb lactose in the small bowel.
· Lactose intolerance—clinical syndrome resulting from malabsorption.
Lactose intake is generally highest during infancy and then decreases with age. About 25% of lactose is absorbed in the small intestine by hydrolyzation with intestinal lactase. In the colon, the remainder of unabsorbed lactose is converted into short-chain fatty acids and hydrogen by the bacterial flora so that it can be absorbed. In some people, a certain degree of lactase deficiency can be mediated by this conversion process.2,3
The exact prevalence of lactose intolerance is not able to be determined, but it is more common among some pediatric populations such as those with recurrent abdominal pain.4,5
Ethnicity significantly impacts risk with worldwide incidence, ranging from 5% to nearly 100%. European and white Americans have the lowest incidence. African Americans, Hispanic Americans, Asian Americans, and Native Americans all have higher incidences, but not nearly as high as is seen in parts of Asia and South America.6 This genetic reduction in lactase enzyme activity is a primary lactose malabsorption problem and is most common in mid-childhood.7 Congenital lactase deficiency, also a cause of primary lactose malabsorption, is a rare autosomal recessive disorder.
Lactose malabsorption also may occur secondary to other gastrointestinal processes such as bacterial overgrowth, intestinal infection (eg, rotavirus, Giardia, and other parasites) or inflammatory processes such as celiac disease, Crohn disease, and immune-related enteropathies.2
Symptoms can be highly variable between individual patients (Table2,6-8). Children with faster transit times through the colon may be more likely to develop more significant symptoms.9 Similarly, foods that decrease gastric emptying times (eg, yogurt) may reduce symptoms of lactose intolerance.2 There is also a small group of patients that demonstrate lactose malabsorption but do not manifest any symptoms.10
Pediatricians take a varied approach to the diagnosis of lactose intolerance. Many pediatricians make a presumptive diagnosis based on history alone with the presence of symptoms with ingestion of lactose products. The diagnosis is often buttressed by symptom resolutions with avoidance and recurrence upon lactose challenge. The 2006 guideline from the American Academy of Pediatrics (AAP) states that a strict lactose-free, 2-week trial with resolution of symptoms and recurrence upon reintroduction is sufficient for diagnosis.2
More objective measures are sometimes preferred, and other indications for testing may include:
· Diagnostic uncertainty.
· Parental concern.
· Desire to avoid lactose-restricted diets.
· Patients in whom the diagnosis may clinically look like lactose intolerance, but the patient is at low risk based on ethnicity.
· Patients with unexplained or severe symptoms.
· Patients in whom the pediatrician suspects lactose intolerance, but the patient does not improve on a lactose-free diet.