A few words should be said about the diagnosis of cystic fibrosis, a hereditary disease carried by a recessive gene. Symptoms usually begin in childhood but may not be manifested until adolescence or occasionally not until adulthood. The disease affects the mucous glands of the body but for some reason seems to affect those of the pancreas more than other organs. The pancreatic secretions become thick and eventually block pancreatic acinar ducts, leading to secondary atrophy of the pancreatic cells. The same process may be found elsewhere; as in the lungs, where inspissated secretions may lead to recurrent bronchopneumonia; and in the liver, where thickened bile may lead to plugging of the small ducts and to a secondary cirrhosis in very severe disease. These patients usually do not have a watery diarrhea, but this is not always easy to ascertain by the history. The diagnosis is made because the sweat glands of the body are also involved in the disease. Although these patients excrete normal volumes of sweat, the sodium and chloride concentration of the sweat is much higher than in normal persons.

Cystic fibrosis in children should be differentiated from celiac disease. Celiac disease is basically the childhood form of the nontropical sprue seen in adults, both of which in many cases seem due to hypersensitivity to gluten. Gluten is found in wheat, oats, and barley and causes both histologic changes and clinical symptoms that are indistinguishable from those of tropical sprue, which is not influenced by gluten. These patients have normal sweat electrolytes, often respond to a gluten-free diet, and behave as ordinary malabsorption syndrome patients.