Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) represents a spectrum of obstructive airway diseases. It includes two key components which are chronic bronchitis - small airways disease and emphysema. 

Epidemiology

The most common cause has historically been, and unfortunately continues to be, smoking. It takes many years of smoking to develop COPD and as such typically patients are older adults. There are however a number of other less common risk factors / aetiologies, each with their own demographics. They include:

• cigarette smoking
• industrial exposure (e.g mining)
• cystic fibrosis
• alpha-1 antitrypsin deficiency (AAT₁ deficiency)
• intravenous drug use
• immune deficiency syndromes
• vasculitides and connective tissue disorders

Clinical presentation

Symptoms include dyspnea on exertion, wheezing, productive cough, pursed-lip breathing, and use of accessory muscles. Patients with chronic bronchitis are classically "blue bloaters," while those with emphysema are known as "pink puffers."  In advanced cases, muscle wasting, asterixis, and peripheral oedema may be seen.

Pathophysiology

In contrast to asthma, the histologic changes of COPD are irreversible and gradually progress over time.  In chronic bronchitis, there is diffuse hyperplasia of mucous glands with associated hypersecretion and bronchial wall inflammation. 

Emphysema involves the destruction of alveolar septa and pulmonary capillaries, leading to decreased elastic recoil and resultant air trapping.  The morphological subtypes of emphysema include centriacinar, which is associated with smoking and spreads peripherally from bronchioles;  panacinar, which is seen in homozygous AAT₁ deficiency and uniformly destroys alveoli;  and paraseptal (distal acinar), which involves the distal airways.

Pulmonary function testing (PFT) reveals airflow obstruction, as evidenced by an increased forced expiratory volume in 1 second to forced vital capacity (FEV₁/FVC) ratio. Administration of bronchodilators has no effect, unlike the reversible obstruction seen in asthma.

Severity classification

The global initiative for chronic obstructive lung disease (GOLD) staging system is a commonly used severity staging system based on air flow limitation. According to this, there are 4 key stages

• stage I - mild - FEV₁ > 80% of normal
• stage II - moderate - FEV₁ = 50-79% of normal
• stage III - severe - FEV₁ = 30-49% of normal
• stage IV - very severe - FEV₁ < 30% of normal or  < 50% of normal with presence of chronic respiratory failure present

The FEV₁:FVC ratio should be < 0.70 for all stages

The GOLD staging system may be insensitive in early stages ¹².

Clinical phenotypes

Several distinct clinical phenotypes have been described ^4,6,8

• emphysema predominant
• airways predominant
  • small airways predominant
  • large airways predominant
• mixed

Radiographic features

Plain film

Findings of chronic bronchitis on chest radiography are nonspecific and include increased bronchovascular markings and cardiomegaly.  Emphysema manifests as lung hyperinflation with flattened hemidiaphragms, a small heart, and possible bullous changes.  On the lateral radiograph, a "barrel chest" with widened anterior-posterior diameter may be visualized. The "saber-sheath trachea" sign refers to marked coronal narrowing of the intrathoracic trachea (frontal view) with concomitant sagittal widening (lateral view).

CT

Findings of COPD may be seen in a variety of CT studies, e.g. contrast enhanced CT, CTPA, staging CT chest, HRCT.

In chronic bronchitis, bronchial wall thickening may be seen in addition to enlarged vessels. Repeated inflammation can lead to scarring with bronchovascular irregularity and fibrosis.

Emphysema is diagnosed by alveolar septal destruction and airspace enlargement, which may occur in a variety of distributions.  Centrilobular emphysema is predominantly seen in the upper lobes with panlobular emphysema predominating in the lower lobes. Paraseptal emphysema tends to occur near lung fissures and pleura.  Formation of giant bullae may lead to compression of mediastinal structures, while rupture of pleural blebs may produce spontaneous pneumothorax / pneumomediastinum.

Treatment and prognosis

There is currently no cure for COPD, but it is highly preventable and treatable.  Risk factor reduction via smoking cessation, occupational health, and air pollution reduction should be instituted.

Management of stable COPD involves the use of bronchodilators, corticosteroids, and other medications (methylxanthines, leukotriene receptor antagonists), as well as supplemental oxygen and pulmonary rehabilitation.  Acute exacerbations are treated with high-dose steroids, short-acting bronchodilators, and antibiotics if indicated.