Differentials
Primary ciliary dyskinesia
SIGNS / SYMPTOMS
Usually not associated with pancreatic insufficiency; chronic purulent middle ear infections and organ laterality defects, which are less common in children with CF.
INVESTIGATIONS
Ciliary biopsy will demonstrate ultrastructural abnormalities of respiratory cilia, or genetic testing may reveal abnormalities in genes that encode key ciliary proteins. Nasal nitric oxide testing can also be used to diagnose primary ciliary dyskinesia.
Primary immunodeficiency
SIGNS / SYMPTOMS
Severe combination of immune deficiency with respiratory infections, IgA deficiency, and IgG1 deficiency; may be associated with non-respiratory infections. Usually not associated with pancreatic insufficiency.
INVESTIGATIONS
Measurement of lymphocyte number and function, neutrophil function, and immunoglobulin levels.
Asthma
SIGNS / SYMPTOMS
Usually not associated with purulent bronchitis. Patients with asthma usually will not demonstrate digital clubbing.
INVESTIGATIONS
There is no diagnostic test. Diagnosis is made clinically. Some children with CF also present with asthma.
Gastro-oesophageal reflux disease (GORD)
SIGNS / SYMPTOMS
Usually not associated with signs or symptoms of malabsorption.
INVESTIGATIONS
Modified barium swallow or gastric emptying studies may be useful in making the diagnosis of chronic aspiration or GORD, but may also be positive in patients with CF.
Chronic aspiration
SIGNS / SYMPTOMS
Usually not associated with signs or symptoms of malabsorption.
INVESTIGATIONS
Modified barium swallow or gastric emptying studies may be useful in making the diagnosis of chronic aspiration or GORD, but may also be positive in patients with CF.
Failure to thrive
SIGNS / SYMPTOMS
May not be associated with respiratory symptoms.
INVESTIGATIONS
Sweat test should be negative if CF is not the cause. However, severe malnutrition causes a falsely elevated sweat test.
Coeliac disease
SIGNS / SYMPTOMS
Patients with coeliac disease will respond to removal of gluten from the diet.
INVESTIGATIONS
Intestinal biopsies.
Protein-losing enteropathy
SIGNS / SYMPTOMS
Loss of serum protein through the gastrointestinal tract. Can be associated with Fontan's procedure, lymphatic disorders, or mucosal erosion.
INVESTIGATIONS
Intestinal biopsies.
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