Restrictive lung diseases

Definition and Characteristics:

• Restrictive lung diseases are a heterogeneous group of disorders characterized by a reduction in lung volumes, especially total lung capacity (TLC).
• These diseases are marked by reduced lung distensibility, compromising lung expansion.
• They differ from obstructive lung diseases like COPD and asthma, which are characterized by increased resistance to airflow due to airway obstruction.

Classification of Causes:

• Intrinsic (Pulmonary Parenchyma Diseases): These involve the lung parenchyma itself.
  • Idiopathic Pulmonary Fibrosis (IPF): Progressive scarring of lung tissue without known cause.
  • Non-Specific Interstitial Pneumonia (NSIP): Inflammatory lung disease with better prognosis than IPF.
  • Cryptogenic Organizing Pneumonia (COP): Inflammatory lung condition characterized by connective tissue plugs in the small airways.
  • Sarcoidosis: Multisystem inflammatory disease often affecting the lungs.
  • Acute Interstitial Pneumonia (AIP): Rapidly progressive interstitial lung disease.
  • Pneumoconiosis: Lung diseases caused by inhalation of dust (e.g., silicosis, asbestosis).
  • Hypersensitivity Pneumonitis: Inflammatory response to inhaled organic dusts.
  • Systemic Sclerosis: Connective tissue disease causing fibrosis.
  • Pulmonary Vasculitis: Inflammation of blood vessels in the lungs.
  • Medications: Drugs like nitrofurantoin, amiodarone, and methotrexate can cause lung fibrosis.
  • Radiation Therapy: Can cause lung scarring.
• Extrinsic (Extrapulmonary Diseases): These originate from outside the lung tissue.
  • Chest Wall Disorders: Such as kyphoscoliosis, obesity.
  • Neuromuscular Disorders: Including muscular dystrophy, amyotrophic lateral sclerosis (ALS).
  • Pleural Conditions: Pleural effusion, trapped lung, pleural scarring.
  • Other Conditions: Ascites, spine deviation.

Causes of pulmonary fibrosis can be divided into those that affect the upper lobes and those predominantly affecting the lower lobes

Upper lobes (SCHART-S)

• silicosis (progressive massive fibrosis), sarcoidosis
• coal workers’ pneumoconiosis (progressive massive fibrosis)
• histiocytosis
• ankylosing spondylitis
• allergic bronchopulmonary aspergillosis
• radiation
• tuberculosis

Lower lobes (RASCO)

• rheumatoid arthritis
• asbestosis
• scleroderma
• cryptogenic fibrosing alveolitis
• other (drugs, e.g. busulphan, bleomycin, nitrofurantoin, hydralazine, methotrexate, amiodarone)

Epidemiology

• Prevalence: Difficult to estimate precisely due to multiple pathological conditions, but up to 3-6 cases per 100,000 persons for intrinsic diseases in the U.S.
• High-Risk Populations:
  • Elderly: Increased prevalence with age.
  • African Americans: Higher prevalence compared to Whites.
  • Females: Slightly higher risk, particularly for sarcoidosis.
  • Obese Individuals: Restrictive patterns associated with higher BMI.
  • Smokers: Increased risk for diseases like IPF.
  • Occupational Exposures: Exposure to substances like asbestos and coal dust.

Pathophysiology

Intrinsic Restriction:

• Inflammation and Fibrosis: Pulmonary parenchyma inflammation leads to fibrosis, thickening alveolar septae, and reducing gas exchange.
• Decreased Compliance: Reduced lung compliance increases the effort required for breathing.

Extrinsic Restriction:

• Mechanical Impediments: Conditions like chest wall deformities or neuromuscular issues impair lung expansion.
• Decreased Compliance: Conditions affecting the rib cage, such as obesity or kyphoscoliosis, also reduce compliance.

Evaluation

Pulmonary Function Tests (PFTs):

• Spirometry: Initial test showing decreased TLC and preserved or increased FEV1/FVC ratio.
• DLCO Measurement: Helps distinguish between intrinsic and extrinsic causes; decreased in intrinsic conditions, normal in extrinsic.
• High-Resolution Computed Tomography (HRCT): Essential for visualizing lung parenchyma and identifying patterns consistent with specific diseases.
• Inflammatory Markers and Autoantibodies: Used to identify underlying systemic or autoimmune conditions.

Management

Idiopathic Pulmonary Fibrosis (IPF):

• Medications: Anti-fibrotic drugs like pirfenidone and nintedanib slow disease progression.
• Supportive Care: Includes oxygen therapy, managing comorbid conditions, and pulmonary rehabilitation.
• Lung Transplantation: Considered for advanced cases.

Autoimmune Conditions:

• Immunosuppressants: Steroids, mycophenolate mofetil, and cyclophosphamide based on disease severity.
• Steroid Therapy: Used for acute exacerbations but not recommended for long-term use.

Obesity:

• Weight Loss: Through diet, exercise, and possibly gastric bypass surgery for morbidly obese patients.

Surgical Interventions:

• Spine Deformities: Surgical correction for severe kyphoscoliosis to improve lung function.

Comprehensive Care:

• Interprofessional Team: Coordination among pulmonologists, rheumatologists, physical therapists, and other healthcare providers to optimize patient care.

Prognosis

• Variable Outcomes: Depends on the specific cause of restriction.
  • IPF: Poor prognosis with median survival of 3-5 years post-diagnosis.
  • Cryptogenic Organizing Pneumonia: Generally good outcomes with appropriate treatment.
  • Acute Interstitial Pneumonia: High mortality (>70% within 3 months).

Complications

• Hypoxemia: Leads to muscle wasting, weight loss, and respiratory failure.
• Sleep Disorders: Such as obstructive sleep apnea (OSA), particularly in obese patients.
• Pulmonary Hypertension and Cor Pulmonale: Result from chronic respiratory failure and lung architecture distortion.