Cystic fibrosis is a genetic disorder characterized by thickening of secretions in the respiratory tract and the gastrointestinal tract. It also affects other organ systems such as liver and kidneys. It is an inherited, autosomal recessive disorder.
The commonest genetic mutation in cystic fibrosis is in the ∆F508 –CFTR gene. This is present in over 90% of the cases of cystic fibrosis. This gene regulates the secretion of chloride ions and absorption of sodium ions in various body secretions.
Lungs are the most commonly affected organs and patients of cystic fibrosis usually present with repeated infections of the respiratory tract as the first symptom, within the first few years of life.
In the normal respiratory tract, the cilia lie above the mucous and in the lining fluid. The ciliary motility helps in the clearing of trapped microorganisms. A normally functioning CFTR gene is responsible for maintaining thin, fluid secretions in the respiratory tract. The product of this gene is a transmembrane ion channel .The chloride ions are secreted into the fluid and reabsorption of sodium and water are prevented, thereby preventing the secretions from becoming thick. In case of cystic fibrosis, since the gene is defective, the chloride ions are trapped within the respiratory epithelial cells and sodium and water are also lacking from the secretions. This leads to production of thick viscid secretions that inhibit ciliary motility. The microorganisms trapped in the thick secretions are not cleared from the respiratory tract, leading to repeated infections that in turn lead to scarring of the respiratory tract. The ultimate result of this cycle of infections and scarring is gradual decrease in lung function. The sinuses are also blocked with thick secretions which lead to colonization with bacteria and infections along with other complications such as scarring and nasal polyps.
In the gastrointestinal tract, the pancreas and the intestines are the most commonly affected organs, with a pathophysiology similar to that seen in the lungs and the respiratory tract. The pancreatic secretions are thick and viscid, affecting the endocrine function as well as the exocrine function due to blockage of pancreatic duct. This manifests as malabsorption syndromes and diabetes mellitus.
An initial clue to the diagnosis of cystic fibrosis in newborns is failure to pass meconium or presence of thick meconium. These children have other malabsorption syndromes as well and present with growth retardation and failure to thrive.
Screening of newborns for specific genetic mutation has become the standard procedure for early diagnosis of cystic fibrosis. This test is of importance as early therapy can be started which does not affect the growth of the child.
Sweat test is another commonly employed method of diagnosis. The basis of sweat test is detection of the amount of sodium and chloride in the patient’s sweat. Pilocarpine is a drug which is used to induce sweating, by applying it locally. The sweat thus induced is collected and analyzed for the levels of sodium and potassium. Patients with cystic fibrosis have an abnormally high level of sodium and potassium in their sweat.
Other investigations such as chest X-ray, abdominal ultrasonography, blood tests such as oral glucose tolerance test and blood glucose levels are used as adjuvants for the diagnoses of conditions arising as complications of cystic fibrosis.
Sputum culture maybe required during the acute phase to start appropriate antibiotic therapy.
Prenatal diagnosis of cystic fibrosis can also be done to determine if the child carries CFTR mutation. Screening of the mutation is also done in case of suspected carriers.
Prognosis of cystic fibrosis is much improved with symptomatic management. Many of the patients live well into adulthood as compared to a majority of them succumbing to the disease, just a few decades earlier.
There is no specific cure for cystic fibrosis. It is only managed symptomatically. Prophylactic antibiotics are given to prevent respiratory infections and infections of paranasal sinuses. Supplements are added to the diet to prevent malabsorption syndromes. Diabetes, which is a common complication, is managed with insulin.
Educating the patients and caregivers is also essential for effective management of the disease.