Cystic fibrosis presenting as diabetes insipidus unresponsive to desmopressin.

The diagnosis of cystic fibrosis (CF) can be confusing when only a part of the typical symptoms is present. In children, CF is usually suspected when dealing with chronic pulmonary symptoms (chronic productive cough, recurrent pneumonia or bronchiolitis). The pediatric gastroenterologist will exclude CF in all children with a meconium ileus, rectal prolaps or a poor weight gain. Atypical CF symptoms are hypochloremic alkalosis, recurrent pancreatitis and increased appetite to compensate for the pancreatic insufficiency. This case report shows how a diagnosis can be delayed when you are mislead by atypical symptoms. It shows the importance of looking in napkins and argues for the inclusion of CF in the differential diagnosis of polyuria in infants.