Respiratory Pathology
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Direct answer
Respiratory pathology divides into obstructive airways disease — emphysema, chronic bronchitis, asthma and bronchiectasis — and restrictive disease, including the pneumoconioses, sarcoidosis, interstitial fibrosis and acute lung injury with diffuse alveolar damage. Pulmonary vascular disease adds embolism, infarction and hypertension with cor pulmonale. Lung cancer closes the topic: central squamous and small cell tumours, peripheral adenocarcinoma, now the commonest subtype, and asbestos-linked mesothelioma, each with a paraneoplastic or buzzword signature.
What you must remember
- Emphysema: permanent airspace enlargement with wall destruction, irreversible; centriacinar in smokers (upper zones), panacinar in alpha-1 antitrypsin deficiency (lower zones, with liver disease); the pink puffer.
- Chronic bronchitis: productive cough three months over two consecutive years; Reid index above 50 per cent; the cyanosed, oedematous blue bloater with cor pulmonale.
- Asthma: type I hypersensitivity with eosinophils, Curschmann spirals of mucus and Charcot-Leyden crystals; reversible obstruction, with aspirin and occupational triggers.
- Bronchiectasis: permanently dilated airways with foul sputum, clubbing and haemoptysis; cystic fibrosis (CFTR delta F508, meconium ileus, salty sweat) and Kartagener syndrome with situs inversus from ciliary dyskinesia.
- Restrictive disease: silicosis with egg-shell hilar nodes and tuberculosis risk (Indian miners and stone workers); coal workers' pneumoconiosis with Caplan nodules in rheumatoid disease; asbestosis with lower-zone fibrosis, pleural plaques and mesothelioma; sarcoidosis with non-caseating granulomas, bilateral hilar nodes, uveitis and hypercalcaemia.
- Vascular and acute injury: pulmonary embolism from deep vein thrombosis with sudden pleuritic pain and haemorrhagic wedge infarcts; ARDS from sepsis or trauma with diffuse alveolar damage, hyaline membranes and refractory hypoxia; neonatal respiratory distress from surfactant deficiency.
- Lung cancer: squamous — central, cavitating, PTHrP hypercalcaemia; small cell — central, neuroendocrine, SIADH, ACTH Cushing and Lambert-Eaton syndrome, chemotherapy-treated; adenocarcinoma — peripheral, scar-associated, commonest overall; Pancoast tumour with Horner syndrome; metastases are the commonest lung tumours.
Common confusion
Emphysema versus chronic bronchitis: irreversible airspace destruction with pursed-lip breathing against mucus-driven airway disease with cyanosis and oedema. Silicosis gives egg-shell nodes and tuberculosis risk; asbestosis gives pleural plaques and mesothelioma. In cancer, match location and syndrome: central cavitating with hypercalcaemia (squamous), central with hyponatraemia or Eaton-Lambert (small cell), peripheral lesion (adenocarcinoma).
Exam-focused takeaway
FMGE asks buzzword-to-diagnosis one-liners — Charcot-Leyden crystals, egg-shell calcification, hyaline membranes, situs inversus with bronchiectasis — plus pink puffer versus blue bloater vignettes. Cancer questions hinge on paraneoplastic-histology pairing, and occupational stems reward the exposure-disease link.
Frequently asked questions
What is the Reid index?
The mucous gland-to-wall thickness ratio in bronchi; above about 50 per cent indicates chronic bronchitis, reflecting mucous hyperplasia behind the productive cough.
Which pneumoconiosis predisposes to tuberculosis?
Silicosis, because crystalline silica cripples macrophages; egg-shell calcification of hilar nodes is the signature. Indian stone grinders remain at risk.
What causes ARDS?
Diffuse alveolar damage from sepsis, trauma, gastric aspiration or pancreatitis, flooding alveoli with protein-rich fluid and hyaline membranes. Refractory hypoxaemia with stiff lungs defines it.
Which lung cancer causes SIADH?
Small cell carcinoma, a neuroendocrine tumour that also secretes ACTH and causes Lambert-Eaton myasthenic syndrome. It responds to chemotherapy rather than surgery.
Why is adenocarcinoma now the commonest lung cancer?
Its share rose as squamous cancer declined with filtered lower-tar cigarettes; it dominates in never-smokers, women and younger patients, arising peripherally, often in scars.
What is a Pancoast tumour?
A superior sulcus tumour invading the sympathetic chain and brachial plexus, producing Horner syndrome with arm pain. Histology is usually squamous carcinoma.