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.