CYSTIC FIBROSIS - Detailed Clinical Note (15 Marks)

1. DEFINITION

• Robbins & Kumar Basic Pathology - the CFTR protein resides on the surface of epithelial cells in the airways, pancreatic ducts, biliary tree, intestine, vas deferens, and sweat glands, resulting in progressive obstructive pulmonary disease.

2. EPIDEMIOLOGY

3. MOLECULAR PATHOGENESIS AND CFTR MUTATIONS

• Classes I-III = "severe" mutations (<10% residual CFTR activity)
• Classes IV-VI = "mild" mutations (<20% residual CFTR activity)

Genotype-Phenotype Correlation

4. PATHOPHYSIOLOGY

1. Loss of CFTR function → failure of Cl⁻ and HCO₃⁻ secretion → reduced surface liquid hydration
2. Compensatory hyperabsorption of Na⁺ (via ENaC channels) → water follows → dehydration of periciliary fluid
3. Airway surface liquid depletion → thick, viscid mucus → impaired mucociliary clearance
4. Mucus stasis → bacterial colonization (S. aureus early; Pseudomonas aeruginosa chronically - mucoid strains)
5. Chronic infection → neutrophilic inflammation → proteases (neutrophil elastase) → airway wall destruction → bronchiectasis
6. Sweat glands: CFTR dysfunction → failure to reabsorb Cl⁻ → elevated sweat chloride (diagnostic hallmark)
7. Pancreatic ducts: viscid secretions obstruct ducts → acinar atrophy, fibrosis → exocrine pancreatic insufficiency (85-90% of patients)

5. CLINICAL FEATURES

A. PULMONARY (90% of patients)

• Chronic productive cough with thick, purulent sputum
• Recurrent respiratory tract infections (S. aureus, H. influenzae, mucoid P. aeruginosa)
• Progressive obstructive lung disease
• Bronchiectasis - the hallmark structural complication
• Bronchitis, bronchiolitis, atelectasis
• Hemoptysis (small streaks common; massive hemoptysis in advanced disease)
• Spontaneous pneumothorax
• Reactive airway disease / wheeze
• Mucoid impaction of bronchi
• Allergic bronchopulmonary aspergillosis (ABPA)
• Respiratory failure - most common cause of death

B. CARDIOVASCULAR (Clinical Cardiology Focus)

• Cor Pulmonale - right heart failure secondary to pulmonary hypertension; results from:
  • Chronic hypoxemia → hypoxic pulmonary vasoconstriction
  • Destruction of pulmonary capillary bed from bronchiectasis and fibrosis
  • Leads to right ventricular hypertrophy and dilation
• Pulmonary artery dilation
• Pulmonary hypertension - a late complication in advanced CF
• Sildenafil has been used for CF-related pulmonary hypertension (limited evidence)
• Cardiac arrhythmias and right heart failure as terminal events

C. UPPER RESPIRATORY TRACT

• Chronic sinusitis (nearly universal)
• Nasal polyps (10-50%)
• Rhinosinusitis

D. GASTROINTESTINAL

• Meconium ileus in neonates (10-25%) - 95% of meconium ileus cases have underlying CF
• Distal intestinal obstruction syndrome (DIOS) - adult equivalent of meconium ileus (18% of adults)
• Rectal prolapse (1-2%)
• Intussusception
• Volvulus
• Fibrosing colonopathy (intestinal strictures)
• GERD (80% of adults)

E. PANCREATIC

• Exocrine pancreatic insufficiency (85-90%) → malabsorption, steatorrhea
• Pancreatitis (1-2%)
• Cystic fibrosis-related diabetes mellitus (4-7%) - unique mixed type (insulin deficiency + resistance)
• Abnormal glucose tolerance (20-30%)

F. HEPATOBILIARY

• Hepatic steatosis (fatty liver) - 7-20%
• Focal biliary cirrhosis (in ~one-third of patients over time)
• Portal hypertension (2-3%, up to 28% in adults)
• Neonatal obstructive jaundice
• Gallstones (8-25%)
• Hypersplenism

G. MUSCULOSKELETAL

• Hypertrophic pulmonary osteoarthropathy (HPOA) - clubbing of fingers and toes
• Arthritis
• Osteoporosis / osteopenia (due to malabsorption of fat-soluble vitamins D and K, and chronic inflammation)

H. REPRODUCTIVE

• Males: Infertility due to congenital bilateral absence of vas deferens (CBAVD) - azoospermia (~98% of CF males)
• Females: Reduced fertility due to thick cervical mucus, delayed puberty from nutritional deficits; ~4% of female CF patients aged 17-37 may be pregnant at any time
• Amenorrhea, delayed puberty

I. SWEAT GLANDS

• Salty sweat - parents may notice salty taste when kissing child
• Excessive salt loss → dehydration, hyponatremia, metabolic alkalosis in infants

J. GENERAL

• Growth failure / failure to thrive (malabsorption)
• Vitamin deficiency (A, D, E, K - fat-soluble vitamins)

6. MORPHOLOGY / PATHOLOGICAL CHANGES

7. DIAGNOSIS

A. Newborn Screening (NBS)

• Blood immunoreactive trypsinogen (IRT) level - elevated in CF due to blocked pancreatic ducts
• CFTR gene mutation analysis on dried blood spot

B. Sweat Chloride Test (Gold Standard)

• Quantitative pilocarpine iontophoresis - stimulates sweating
• Diagnostic: Cl⁻ >60 mmol/L (two separate occasions)
• Borderline: 30-59 mmol/L
• Normal: <30 mmol/L
• False positives: adrenal insufficiency, hypothyroidism, nephrogenic DI, ectodermal dysplasia, malnutrition, glycogen storage disease type I

C. Genetic Analysis

• Over 2500 CFTR mutations described
• CFTR gene sequencing if mutation not identified on screening panel
• Two disease-causing CFTR variants in trans configuration = diagnostic

D. Pulmonary Function Tests (PFTs)

• Obstructive pattern (reduced FEV1, FEV1/FVC ratio)
• FEV1 used to track disease severity and predict outcomes
• Decline in FEV1 = most reliable marker of disease progression

E. Chest X-Ray / CT Chest

• Hyperinflation, peribronchial thickening, mucus plugging
• Bronchiectasis (ring shadows, tram-tracks)
• Upper lobe predominance in CF bronchiectasis

F. Additional Tests

• Sputum culture and sensitivity (Pseudomonas aeruginosa, MRSA)
• Nasal potential difference measurement (CFTR function)
• Pancreatic function: fecal elastase, 72-hour fecal fat

8. MANAGEMENT

A. Pulmonary - Airway Clearance

• Chest physiotherapy (CPT) - percussion and postural drainage (hallmark BPT intervention)
• High-frequency chest wall oscillation (HFCWO) - "Vest" device
• Active cycle of breathing technique (ACBT)
• Oscillatory PEP devices (Flutter, Acapella)

B. Aerosolized Agents

• Dornase alfa (DNase) - recombinant human DNase; cleaves extracellular DNA from neutrophils, reducing mucus viscosity
• Hypertonic saline (7%) - hydrates airway mucus, stimulates cough, improves mucociliary clearance

C. Antibiotics

• Acute exacerbations: IV antibiotics targeting Pseudomonas (anti-pseudomonal penicillins, aminoglycosides, fluoroquinolones)
• Chronic Pseudomonas colonization: aerosolized tobramycin or aztreonam alternating monthly
• Chronic azithromycin - reduces exacerbation frequency (immunomodulatory effect)

D. CFTR Modulator Therapy (Targeted Therapy)

E. Nutritional Management

• High-calorie, high-fat diet (120-150% of normal caloric requirements)
• Pancreatic enzyme replacement therapy (PERT) - lipase + amylase + protease capsules with meals
• Fat-soluble vitamin supplementation: A, D, E, K
• Management of CF-related diabetes: insulin therapy

F. Management of Cardiovascular Complications

• Cor pulmonale: supplemental O₂ therapy (mainstay), diuretics (cautiously), pulmonary vasodilators (sildenafil - limited evidence)
• Optimize pulmonary treatment to reduce hypoxemia
• Avoid beta-blockers (may worsen bronchospasm)
• Lung transplantation - definitive therapy in end-stage disease; bilateral sequential lung transplantation improves survival

G. Lung Transplantation

• Indicated for end-stage CF (FEV1 <30%, rapid decline, recurrent life-threatening hemoptysis, or hypercapnia)
• Bilateral sequential lung transplant is the procedure of choice
• 5-year survival post-transplant ~50%

9. CARDIOVASCULAR MANIFESTATIONS IN DETAIL (Cardiology Focus)

Cor Pulmonale in CF

• CF is listed as a predisposing disease to cor pulmonale (Robbins & Kumar - Table 9.3 - Disorders Predisposing to Cor Pulmonale includes: COPD, Diffuse pulmonary interstitial fibrosis, Pneumoconiosis, Cystic fibrosis, Bronchiectasis)

1. Chronic hypoxemia from obstructive lung disease and V/Q mismatch
2. Hypoxic pulmonary vasoconstriction → elevated pulmonary vascular resistance
3. Destruction of pulmonary capillary bed by bronchiectasis, fibrosis, and emphysema
4. Pulmonary artery remodeling → fixed pulmonary hypertension
5. Right ventricle works against chronically elevated afterload → RV hypertrophy → eventually RV failure

• Elevated JVP
• Right ventricular heave
• Loud P2 (pulmonary component of S2)
• Tricuspid regurgitation murmur
• Peripheral edema
• Hepatomegaly (congestive)

• RV hypertrophy and dilation
• Tricuspid annular plane systolic excursion (TAPSE) reduced
• Elevated RVSP (right ventricular systolic pressure)
• Pulmonary artery dilation

• Supplemental O₂ (target SpO₂ >90%) - reduces hypoxic vasoconstriction
• Optimal CF pulmonary treatment (antibiotics, airway clearance, modulators)
• Diuretics: furosemide - reduce preload, edema
• Sildenafil (PDE-5 inhibitor): used for CF-related pulmonary hypertension (Goldman-Cecil Medicine)
• Lung transplantation - only definitive therapy

10. PROGNOSIS

• Median survival has dramatically improved: now >47 years in many centers (Sleisenger & Fordtran)
• Most common cause of death: respiratory failure (>90% of deaths)
• Poor prognostic indicators: FEV1 <30%, chronic Pseudomonas colonization, malnutrition, frequent exacerbations, diabetes, female sex (historically)
• CFTR modulator therapy (especially Trikafta) has transformed outcomes - significant improvement in FEV1, nutritional status, quality of life, and reduction in hospitalizations

11. SUMMARY TABLE

• Robbins, Cotran & Kumar: Pathologic Basis of Disease - Chapter 10 (Cystic Fibrosis genetics and morphology)
• Harriet Lane Handbook, 23rd ed. - Chapter 25 (Clinical manifestations and management)
• Murray & Nadel's Textbook of Respiratory Medicine - Chapters 16, 30
• Sleisenger & Fordtran's GI and Liver Disease - Table 57.3 (GI manifestations frequency)
• Robbins & Kumar Basic Pathology - Table 9.3 (Cor pulmonale predisposing disorders)
• Goldman-Cecil Medicine - Pulmonary hypertension management in CF