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Cystic Fibrosis

Aug 24, 20254 min read

Cystic Fibrosis

Background

Cystic fibrosis (CF) is a disease of exocrine gland function that involves multiple organ systems but chiefly results in chronic respiratory infections, pancreatic enzyme insufficiency, and associated complications.

Pathophysiology

  • Cystic fibrosis is caused by defects in the CF gene, which codes for a protein transmembrane conductance regulator (CFTR).

  • CFTR functions as a chloride channel and is regulated by cAMP.

  • Mutations in the CFTR gene result in abnormalities of cAMP-regulated chloride transport across epithelial cells on mucosal surfaces.

  • Cystic fibrosis is an autosomal recessive disease.

  • Its estimated heterozygote frequency in white people is up to 1 in 20. Median survival age is 36.9 years.

History

  • Median age at diagnosis of cystic fibrosis is 6-8 months.
  • Approximately 10% of patients with cystic fibrosis remain pancreatic sufficient; these patients tend to have a milder course.

Neonates: may present with meconium ileus or, rarely, anasarca.

Patients younger than 1 year present with:

  • wheezing, coughing, recurring respiratory infections, pneumonia,
  • steatorrhea, failure to thrive, or both.

Patients diagnosed later in childhood:

  • are more likely to have pancreatic sufficiency and often present with chronic cough and sputum production.

Meconium ileus

occurs in 7-10% of patients with CF.

  • Simple meconium ileus presents with abdominal distension at birth, progressing to failure to pass meconium, bilious vomiting, and progressive abdominal distension.

  • Complicated meconium ileus presents more dramatically at birth with severe abdominal distention, accompanied by abdominal wall erythema and edema.

    • Intestinal obstruction at birth (e.g., volvulus, intestinal atresia, perforation, meconium peritonitis).
    • Delayed passage of meconium (>24-48 hours after birth).
    • Prolonged cholestatic jaundice.

Pancreatic insufficiency:

  • Fat-soluble vitamin deficiency and malabsorption of fats, proteins, and carbohydrates.
  • Malabsorption results in steatorrhea, characterized by frequent, poorly formed, large, bulky, foul-smelling, greasy stools that float in water. Some patients have anorexia without obvious steatorrhea.
  • Failure to thrive, flatulence or foul-smelling flatus, recurrent abdominal pain, and abdominal distention.
  • Intussusception (ileocecal).
  • Rectal prolapse.
  • Jaundice or GIT bleeding as a result of hepatobiliary involvement.

Respiratory Tract Manifestations

  • Chronic or recurrent cough: dry and hacking at the beginning and produce mucoid (early) and purulent (later) sputum. - psuodomonas most common
  • Prolonged symptoms of bronchiolitis in infants.
  • Paroxysmal cough followed by vomiting.
  • Recurrent wheezing, recurrent pneumonia, atypical asthma, pneumothorax, hemoptysis, and digital clubbing are all complications.
  • Dyspnea on exertion, history of chest pain, recurrent sinusitis, nasal polyps; Sinusitis, and hemoptysis.

Urogenital Tract Manifestations

  • Undescended testicles or hydrocele.
  • Males are frequently sterile because of the absence of the vas deferens.
  • In females, decreased fertility, secondary sexual development is often delayed.
  • Amenorrhea may occur in females with severe nutritional or pulmonary involvement.

Physical Examination - Respiratory System

  • Rhinitis

  • Nasal polyps

  • Tachypnea

  • Respiratory distress with retractions

  • Wheeze or crackles

  • Cough (dry or productive of mucoid or purulent sputum)

  • Increased anteroposterior diameter of chest

  • Clubbing

  • Cyanosis

  • Hyperresonant chest upon percussion

  • Crackles are heard acutely in associated pneumonitis or bronchitis and chronically with bronchiectasis.

  • Swelling of submandibular gland or parotid gland.

  • Abdominal distention.

  • Hepatosplenomegaly (fatty liver and portal hypertension).

  • Rectal prolapse.

  • Dry skin (vitamin A deficiency).

  • Cheilosis (vitamin B complex deficiency).

  • Scoliosis/Kyphosis.

Differential Diagnoses

  • Acute Sinusitis
  • Bronchiolitis
  • Failure to Thrive
  • Asthma
  • Bronchiectasis
  • Celiac Disease (Sprue)
  • Primary Ciliary Dyskinesia
  • Short Stature

Diagnostic Confirmation

Requirements for a CF diagnosis include either positive genetic testing or positive sweat chloride test findings (>60 mEq/L) and one of the following:

  • Typical chronic obstructive pulmonary disease
  • Documented exocrine pancreatic insufficiency
  • Positive family history (usually affected sibling).

Prenatal Testing:

  • Noninvasive CFTR analysis involves a technique for recovering DNA from cells obtained by buccal brushing.
  • Amniocentesis.

Neonatal Testing:

  • Immunoreactive trypsinogen (IRT) elevated in infants with cystic fibrosis and genetic testing.

Other Tests for CF

  • Comprehensive metabolic panel (CMP): Urea, electrolytes, Ca, LFT.
  • Complete blood count (CBC)—another test for general health and to help detect infections.
  • Glucose and hemoglobin A1c—to detect, diagnose, and monitor diabetes.
  • Amylase and lipase—to detect problems with the pancreas.
  • Fecal fat—to identify malabsorption and pancreatic insufficiency.
  • Semen analysis—to detect infertility.
  • Sputum cultures—to help diagnose lung infections.
  • Chest X-rays, upper GI and small bowel series, and lung function tests.

Treatment

The primary goals of CF treatment include the following:

  • Maintaining lung function as near to normal as possible by controlling respiratory infection and clearing airways of mucus.

  • Administering nutritional therapy (i.e., enzyme supplements, multivitamin and mineral supplements) to maintain adequate growth.

  • Managing complications.

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