COPD Pathology
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Direct answer
Chronic obstructive pulmonary disease comprises chronic bronchitis and emphysema, both driven overwhelmingly by smoking and defined by persistent airflow limitation. Chronic bronchitis is a clinical diagnosis — productive cough on most days for three consecutive months in two successive years — with mucous gland hypertrophy raising the Reid index and small-airway inflammation. Emphysema is the pathological counterpart: permanent enlargement of airspaces distal to the terminal bronchiole with wall destruction and minimal fibrosis, subtyped by the part of the acinus destroyed — centriacinar in smokers, panacinar in alpha-1 antitrypsin deficiency. Both culminate in hyperinflation, hypoxaemia and, in advanced disease, cor pulmonale.
What you must remember
- Chronic bronchitis definition: sputum-producing cough for at least three months over two consecutive years, with no other cause; histology shows bronchial mucous gland hypertrophy and goblet cell metaplasia with mucous plugging.
- Reid index: ratio of mucous gland thickness to bronchial wall thickness between epithelium and cartilage, normally below about 0.4 and increased in chronic bronchitis — a standard pathology question.
- Centriacinar emphysema: respiratory bronchioles of the upper lobes destroyed, typical of smokers and coal workers, with spared distal alveoli early.
- Panacinar emphysema: entire acinus from respiratory bronchiole to alveoli, lower-lobe predominant, the signature of alpha-1 antitrypsin deficiency — screen young or non-smoking emphysema patients.
- Paraseptal (distal acinar) emphysema: subpleural and along septa at the apices, forming bullae that rupture to cause spontaneous pneumothorax in young tall men; irregular (paracicatricial) emphysema follows scarring.
- Clinical phenotypes: "blue bloater" — chronic bronchitis with cough, sputum, oedema, hypercapnia and cor pulmonale; "pink puffer" — emphysema with pursed-lip breathing, cachexia and relatively preserved gases until late.
- Complications and care: recurrent infection, polycythaemia, pulmonary hypertension and right heart failure; smoking cessation plus bronchodilators, rehabilitation, vaccination and oxygen for chronic hypoxaemia form standard management per current guidance, including India's national programme framing for COPD.
Common confusion
Emphysema versus chronic bronchitis overlap but differ pathologically: emphysema destroys alveolar walls without significant fibrosis, while chronic bronchitis is airway disease with mucus and inflammation but intact alveoli. Asthma is separated by reversibility and its eosinophilic, TH2-driven inflammation, unlike the neutrophilic, macrophage-rich inflammation of COPD. Finally, panacinar emphysema with basal distribution and hepatic disease or family history should prompt alpha-1 antitrypsin testing rather than another course of inhalers.
Exam-focused takeaway
Questions pair histology with phenotypes: a Reid-index photograph points to chronic bronchitis, apical bullae after pneumothorax point to paraseptal disease, and basilar panacinar destruction in a young adult points to protease inhibitor deficiency. Expect one-liners on the definition of chronic bronchitis, the acinar segment destroyed in each emphysema type, and cor pulmonale as the cardiac complication. The imbalance of proteases and antiproteases is the mechanism most often tested.
Frequently asked questions
How is chronic bronchitis defined?
Productive cough on most days for at least three months over two consecutive years without another cause; pathologically the Reid index is increased.
What is the Reid index?
The thickness of the bronchial mucous gland layer divided by the wall thickness from epithelium to cartilage — normally up to about 0.4 and raised in chronic bronchitis.
Which emphysema type marks alpha-1 antitrypsin deficiency?
Panacinar emphysema, destroying the whole acinus with lower-lobe predominance in young or non-smoking patients.
Why does emphysema cause airflow obstruction despite airway sparing?
Loss of elastic recoil from alveolar destruction collapses small airways during expiration, trapping air and limiting flow.
What is cor pulmonale in COPD?
Right ventricular hypertrophy and failure secondary to hypoxic pulmonary vasoconstriction and pulmonary hypertension, seen especially in chronic bronchitis.