Cystic Fibrosis — MCQs

10 questions

What is the chance of a child having cystic fibrosis if both parents are carriers of the disease?

Which antibiotic is best suited for Pseudomonas aeruginosa in a CF patient?

A 3-year-old child is evaluated by a pediatrician for poor growth despite excessive food intake. The mother reports that the child's stools are bulky, foul-smelling, and difficult to flush because they float. Determination of which of the following would most likely be diagnostic in this case?

What is the most common genetic abnormality in cystic fibrosis?

Which of the following exocrine glandular ducts are not obstructed in cystic fibrosis?

A 10-year-old male child presenting with complaints of poor growth, poor appetite, short stature, clubbing, and recurrent chest infections, along with steatorrhea, is most likely diagnosed with what?

Which of the following conditions is most associated with digital clubbing in children?

A child is brought to the paediatric OPD with fever of 24 hours duration. History reveals 3 episodes of chest infection and passage of foul smelling stools. The most probable diagnosis is-

Which of the following is an indication for lung transplantation?

Q10

Organic causes of constipation in infants include all of the following EXCEPT:

Cystic Fibrosis Indian Medical PG Practice Questions and MCQs

Question 1: What is the chance of a child having cystic fibrosis if both parents are carriers of the disease?

A. 75%
B. 25% (Correct Answer)
C. 50%
D. 0%
E. 100%

Explanation: ***50%*** - If one parent is affected by cystic fibrosis (CF), they are **homozygous for the CFTR mutation**, while the normal parent is likely **homozygous for the normal allele**. - Each child has a **50% chance** of inheriting the **mutated allele** from the affected parent, resulting in an **autosomal recessive** inheritance pattern [1]. *70%* - This percentage does not reflect the inheritance probabilities associated with **autosomal recessive traits** [1], such as cystic fibrosis. - In heterozygous and normal arrangements, the calculation does not support a **70%** inheritance chance of the disease. *80%* - Similarly, an **80% chance** is inaccurate as cystic fibrosis requires two mutated alleles for the disease to manifest [1]. - The inheritance pattern does not allow for a higher than **50% chance** when one parent is normal. *25%* - A **25% chance** applies if both parents were carriers of the CFTR mutation [1]. However, with only one affected parent, this percentage does not apply. - The maximum **chance of inheritance** from one affected and one normal parent is accurately stated as **50%**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 53-54.

Question 2: Which antibiotic is best suited for Pseudomonas aeruginosa in a CF patient?

A. Ceftazidime (Correct Answer)
B. Clindamycin
C. Amoxicillin
D. Ciprofloxacin

Explanation: ***Ceftazidime*** - **Ceftazidime** is the **gold standard** first-line treatment for *Pseudomonas aeruginosa* in CF patients according to **CF Foundation guidelines**, often combined with an **aminoglycoside** like tobramycin. - It demonstrates **superior efficacy** against P. aeruginosa with lower propensity for **resistance development** compared to other antibiotics, making it the preferred choice for acute exacerbations. *Clindamycin* - **Clindamycin** is primarily effective against **gram-positive bacteria** and **anaerobes**; it has **no activity** against *Pseudomonas aeruginosa*. - It is commonly used for skin and soft tissue infections or anaerobic infections, but is not suitable for treating **gram-negative rods** like *P. aeruginosa*. *Amoxicillin* - **Amoxicillin** is a broad-spectrum penicillin effective against many **gram-positive** and some **gram-negative bacteria**, but it **completely lacks activity** against *Pseudomonas aeruginosa*. - Even with beta-lactamase inhibitors (amoxicillin-clavulanate), it has **no antipseudomonal coverage** and is not appropriate for CF-related Pseudomonas infections. *Ciprofloxacin* - While **ciprofloxacin** has good antipseudomonal activity and offers advantages like **oral bioavailability** and **lung penetration**, it is primarily used for **maintenance therapy** or mild outpatient cases. - It has concerns about **resistance development** when used as monotherapy and is not considered the **first-line choice** for acute P. aeruginosa infections in CF patients.

Question 3: A 3-year-old child is evaluated by a pediatrician for poor growth despite excessive food intake. The mother reports that the child's stools are bulky, foul-smelling, and difficult to flush because they float. Determination of which of the following would most likely be diagnostic in this case?

A. Na+ in cerebrospinal fluid
B. Na+ in urine
C. Na+ in sweat (Correct Answer)
D. Na+ in serum

Explanation: ***Na+ in sweat*** - This clinical presentation of **poor growth despite excessive food intake** (due to malabsorption) and **bulky, foul-smelling, floating stools** (steatorrhea) is highly suggestive of **cystic fibrosis (CF)**. - The **sweat test** is the diagnostic gold standard for CF. While the test measures both Na+ and Cl- in sweat, the **diagnostic criterion is based primarily on elevated chloride concentration** (Cl- ≥60 mmol/L). In CF, both sodium and chloride are elevated due to defective CFTR channel function. - This patient's symptoms of malabsorption result from **pancreatic insufficiency**, a common manifestation of CF. *Na+ in cerebrospinal fluid* - Measuring Na+ in cerebrospinal fluid is typically done to evaluate neurological conditions or electrolyte imbalances affecting the **central nervous system**, which is not indicated here. - There is no direct link between CSF Na+ levels and the malabsorption or growth failure described in this case. *Na+ in urine* - Urinary Na+ levels are used to assess **renal function** and overall **fluid and electrolyte balance**, and are relevant in conditions like **dehydration**, **kidney disease**, or **adrenal disorders**. - These tests are not primary diagnostic tools for the gastrointestinal and growth issues described, which point more towards a malabsorption syndrome. *Na+ in serum* - Serum Na+ levels reflect the body's overall **hydration status** and are crucial for diagnosing **hyponatremia** or **hypernatremia**. - While important for general medical assessment, serum Na+ levels do not specifically diagnose the underlying cause of malabsorption and steatorrhea seen in this child.

Question 4: What is the most common genetic abnormality in cystic fibrosis?

A. ΔF508 (Correct Answer)
B. R117H
C. G551D
D. G542X

Explanation: ***ΔF508*** - This mutation accounts for approximately **70% of all cystic fibrosis (CF) cases** worldwide, making it the most common genetic abnormality [1]. - It results in the deletion of a **phenylalanine residue** at position 508 in the **CFTR protein**, leading to misfolding and degradation [1]. *R117H mutation* - This is a rare **splice-site mutation** that can cause a milder form of CF or CFTR-related disorders. - It results in reduced CFTR protein function but is not the most common mutation. *G551D mutation* - This mutation is a **class III gating mutation**, meaning it impairs the opening of the **chloride channel** rather than its synthesis or trafficking. - It is relatively rare and is specifically targeted by CFTR modulator therapies like ivacaftor. *G542X mutation* - This is a **class I nonsense mutation** that introduces a premature stop codon, leading to a truncated and non-functional CFTR protein [1]. - While it causes severe CF, it is less common than the ΔF508 mutation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, p. 476.

Question 5: Which of the following exocrine glandular ducts are not obstructed in cystic fibrosis?

A. Pancreas
B. Lung
C. Sweat gland (Correct Answer)
D. None of the options

Explanation: ***Sweat gland*** - In cystic fibrosis, the **CFTR protein** in sweat glands is defective, leading to **impaired chloride reabsorption** and excessively salty sweat [1]. - This defect causes dysfunctional sweat production but **does not result in obstruction** of the sweat gland ducts, which continue to secrete. *Pancreas* - The **exocrine pancreatic ducts** are frequently obstructed in cystic fibrosis due to the production of **thick, sticky mucus**. - This obstruction leads to maldigestion and **pancreatic insufficiency**, requiring enzyme replacement therapy. *Lung* - **Bronchial ducts** and airways in the lungs are severely affected by the accumulation of **viscous mucus**, leading to chronic obstruction [1]. - This obstruction impairs mucociliary clearance, making patients susceptible to recurrent **pulmonary infections** and progressive lung damage [1], [2]. *None of the options* - This option is incorrect because sweat glands are indeed not obstructed, making option C the appropriate answer.

Question 6: A 10-year-old male child presenting with complaints of poor growth, poor appetite, short stature, clubbing, and recurrent chest infections, along with steatorrhea, is most likely diagnosed with what?

A. Celiac Disease
B. Cystic fibrosis (Correct Answer)
C. Biliary cirrhosis
D. Bronchiectasis

Explanation: ***Cystic fibrosis*** - The constellation of **poor growth**, **short stature**, **recurrent chest infections**, **clubbing**, and **steatorrhea** is highly indicative of cystic fibrosis. - **Cystic fibrosis** is a genetic disorder affecting exocrine glands, leading to thick, sticky mucus that clogs the lungs and pancreas, causing malabsorption. *Celiac Disease* - **Celiac disease** primarily affects the small intestine, leading to malabsorption and poor growth. - While it can cause steatorrhea and poor growth, it does not typically present with recurrent chest infections or significant clubbing. *Biliary cirrhosis* - **Biliary cirrhosis** involves liver damage and can cause steatorrhea due to impaired bile flow. - However, it is not typically associated with recurrent chest infections or prominent clubbing unless advanced. *Bronchiectasis* - **Bronchiectasis** is characterized by permanent dilation of the bronchi, leading to chronic cough and recurrent respiratory infections. - While it can cause clubbing and recurrent chest infections, it does not directly cause steatorrhea or poor growth as a primary feature, although malnutrition can occur secondary to chronic illness.

Question 7: Which of the following conditions is most associated with digital clubbing in children?

A. Croup
B. Bronchiolitis
C. Asthma
D. Cystic fibrosis (Correct Answer)

Explanation: ***Cystic fibrosis*** - **Cystic fibrosis** is a common cause of **digital clubbing** in children due to chronic hypoxemia and lung disease, leading to abnormal growth of connective tissue at the nail beds. - The chronic lung infections, bronchiectasis, and airway obstruction characteristic of cystic fibrosis contribute to persistent **tissue hypoxia**, which is a primary driver of clubbing. *Croup* - Croup is an acute viral infection of the upper airway, primarily characterized by a **barking cough** and **stridor**, and generally resolves within a week without chronic complications like clubbing. - It does not cause chronic hypoxemia necessary for the development of digital clubbing. *Bronchiolitis* - **Bronchiolitis** is an acute viral infection of the lower respiratory tract, most common in infants, causing wheezing and respiratory distress, but it is typically a **short-lived illness** without chronic sequelae leading to clubbing. - This condition does not cause prolonged enough or severe enough **hypoxia** to result in clubbing. *Asthma* - While severe, uncontrolled **asthma** can cause intermittent hypoxia, it is typically not associated with chronic digital clubbing, especially in children, unless there are other coincident chronic lung conditions. - Digital clubbing is rare in asthma and often suggests an alternate or co-existing pathology, such as **bronchiectasis** or **cystic fibrosis**.

Question 8: A child is brought to the paediatric OPD with fever of 24 hours duration. History reveals 3 episodes of chest infection and passage of foul smelling stools. The most probable diagnosis is-

A. Crigler-Najjar Syndrome
B. Maple Syrup urine Disease
C. Bilirubin Conjugation Defect
D. Cystic Fibrosis (Correct Answer)

Explanation: ***Cystic Fibrosis*** - Recurrent **chest infections** and **foul-smelling stools** (due to pancreatic insufficiency leading to malabsorption) are classic hallmarks of cystic fibrosis. - This genetic disorder primarily affects the **lungs** and **digestive system**, leading to thick, sticky mucus. *Crigler-Najjar Syndrome* - This syndrome is a rare genetic disorder characterized by severe **unconjugated hyperbilirubinemia**, leading to **jaundice** and potential neurological damage. - It does not typically present with recurrent chest infections or foul-smelling stools. *Maple Syrup urine Disease* - This is an **amino acid metabolism disorder** leading to the accumulation of branched-chain amino acids, characterized by a distinctive "maple syrup" odor in the urine. - It presents with neurological symptoms, feeding difficulties, and developmental delay, not primarily chest infections and foul-smelling stools. *Bilirubin Conjugation Defect* - This refers to conditions like Gilbert's syndrome or Crigler-Najjar syndrome, which cause varying degrees of **unconjugated hyperbilirubinemia** and **jaundice**. - It does not explain the recurrent respiratory infections or malabsorption symptoms like foul-smelling stools.

Question 9: Which of the following is an indication for lung transplantation?

A. COPD
B. Alpha-1 antitrypsin deficiency
C. Cystic fibrosis and bronchiectasis
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - **COPD**, **Alpha-1 antitrypsin deficiency**, and **Cystic fibrosis** with **bronchiectasis** are all common indications for lung transplantation when medical management fails and the patient meets other criteria. - Lung transplantation is considered for patients with **end-stage lung disease** who have a high risk of death within 1-2 years without transplantation, and who have no significant comorbidities. *COPD* - While many patients with **COPD** manage with medical therapy, those with severe disease, frequent exacerbations, and **declining lung function** despite maximal treatment can be candidates for lung transplantation. - **End-stage COPD** is a significant cause of morbidity and mortality, making transplantation a viable option for selected patients. *Alpha-1 antitrypsin deficiency* - This genetic disorder primarily affects the lungs, leading to **early-onset emphysema** and **bronchiectasis**, particularly in non-smokers. - When the lung damage progresses to a severe and life-threatening stage, **lung transplantation** becomes a treatment option. *Cystic fibrosis and bronchiectasis* - **Cystic fibrosis** often leads to severe, progressive **bronchiectasis** and chronic lung infections, resulting in **end-stage lung disease**. - For these patients, especially those with intractable daily symptoms and **declining respiratory function**, lung transplantation can significantly improve quality of life and survival.

Question 10: Organic causes of constipation in infants include all of the following EXCEPT:

A. Hirschsprung's disease
B. Cystic fibrosis
C. Hypothyroidism
D. Infantile dyschezia (Correct Answer)

Explanation: ***Infantile dyschezia*** - This is a **functional condition** where infants strain and cry before passing a soft stool, due to a lack of coordination between relaxing the pelvic floor and increasing intra-abdominal pressure. It is not an organic cause of constipation. - The stool consistency in infantile dyschezia is typically **soft**, differentiating it from true constipation. *Hirschsprung's disease* - This is an **organic cause of constipation** due to the absence of **ganglion cells** in the distal colon, leading to a functional obstruction. - Infants typically present with **failure to pass meconium** within the first 24-48 hours of life, distended abdomen, and forceful expulsion of stool upon rectal examination. *Cystic fibrosis* - This is an **organic cause of constipation** in infants due to the production of thick, sticky intestinal secretions, often leading to **meconium ileus** at birth. - Constipation can also result from **pancreatic insufficiency**, which impairs fat digestion and absorption, leading to hard, dry stools later in infancy. *Hypothyroidism* - This is an **organic cause of constipation** because thyroid hormones are essential for normal gastrointestinal motility. - Infants with hypothyroidism often present with **decreased bowel movements**, lethargy, poor feeding, and prolonged jaundice.

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