The evaluation of the child whose rate of growth is impaired or who fails to thrive frequently includes evaluation for malabsorption. Although diarrhea may be a cardinal feature of most malabsorptive disorders, it may not be present or appreciated. The pediatrician must recognize manifestations of malabsorptive disease so as to establish early diagnosis and initiate treatment to minimize the long-term consequences of malnutrition.
To establish a diagnosis requires an understanding of the physiology and pathophysiology of digestion and absorption. Digestion begins as an intraluminal event, requiring oral, gastric, and pancreatic enzymes and bile acids for micelle formation. Absorption requires adequate mucosal surface area, brush border and intracellular enzymes, and specific transport mechanisms. The diseases and their symptoms vary with age and even with socioeconomic conditions. For example, in the developing world, malabsorption most often is encountered in the context of mucosal injury from recurrent or persistent infections, perpetuated by poor hygiene and nutrition.
Infants present predominantly with congenital disorders of specific nutrient digestion or absorption (Table 1). Older children typically have an acquired mucosal disease such as those listed in Table 2. The overlap is tremendous, and diseases such as cystic fibrosis and gluten-sensitive celiac disease present in different manners at different ages.