Respiratory System for NEET PG Pathology: Pneumonia, Lung Abscess, COPD, Bronchiectasis, Pneumoconioses, Lung Cancer, Mesothelioma

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🎯 Exam priority: High. Expect: match a dust to its disease, the chronic bronchitis definition, alpha-1 antitrypsin, lung abscess site after aspiration, the commonest lung cancer type, Pancoast/Horner, and asbestos-related pleural disease and mesothelioma.

CBME mapping: PA 25.1–25.7. Tuberculosis is in article 7; paraneoplastic syndromes of lung cancer in article 4.

Occupational lung disease, airways and infection, lung cancer and mesothelioma. Drawn by TrackNation.

Infection

• Pneumonia: Streptococcus pneumoniae is the commonest pathogen in all ages, settings and regions. Other community-acquired causes: H. influenzae, atypicals (Chlamydia pneumoniae, Mycoplasma, Legionella) and viruses.

• Lung abscess: a pus-filled cavity, usually from aspiration of oral secretions; anaerobes dominate. It forms in segments that are dependent when lying down — posterior segments of the upper lobes, superior or lateral basal segments of the lower lobes — with an air-fluid level.

• Acute hypoxaemic respiratory failure: PaO2 < 60 mm Hg, PaO2/FiO2 < 300 or SpO2 < 88%.

Obstructive Airway Disease

• COPD = chronic obstructive bronchitis and/or emphysema. Smoking is the main cause, yet only about 15% of smokers develop clinical COPD. Chronic bronchitis: productive cough on most days for at least 3 months a year for 2 consecutive years.

• Alpha-1 antitrypsin deficiency: unchecked proteases destroy lung tissue (emphysema in adults); abnormal protein stuck in the liver causes liver disease. A cause of COPD in non-smokers.

• Asthma: bronchoconstriction, airway oedema and inflammation, hyperreactivity and remodelling, driven by Th2 cells, eosinophils and mast cells.

• Bronchiectasis: permanent dilation and destruction of large bronchi from chronic infection — cystic fibrosis, immune defects, primary ciliary dyskinesia; chronic cough with purulent sputum.

Occupational Lung Disease

• Silicosis (crystalline silica): nodular fibrosis, upper-lobe 1–3 mm nodules, eggshell-calcified hilar nodes; higher risk of TB, COPD and lung cancer.

• Coal worker pneumoconiosis: from mild disease to progressive massive fibrosis; with rheumatoid arthritis → Caplan syndrome (rheumatoid nodules).

• Asbestosis: peripheral lower-lobe fibrosis; asbestos bodies support (but are not needed for) diagnosis. Asbestos pleural disease: plaques, calcification, thickening, effusion and mesothelioma (latency 30–50 years).

• Byssinosis: cotton, flax and hemp dust (endotoxin) — chest tightness worst on the first working day of the week. Chronic beryllium disease: granulomas that mimic sarcoidosis.

Lung Cancer

• The leading cause of cancer death worldwide; about 85% linked to smoking, but 15–20% of patients never or barely smoked. Risk falls after quitting but never returns to baseline. Radon is the second cause in the US; asbestos, arsenic and other carcinogens add risk.

• Small cell vs non-small cell. Adenocarcinoma is the commonest subtype, especially in never-smokers; targetable drivers (EGFR, ALK) are mostly found here. Squamous cell carcinoma carries TP53 mutations in about 91%.

• Pancoast (superior sulcus) tumour: invades brachial plexus, pleura or ribs → shoulder and arm pain, hand weakness, and Horner syndrome (ptosis, miosis, anhidrosis) when the sympathetic chain is involved. Small cell paraneoplastic syndromes: article 4.

Traps the Examiner Sets

• Silicosis = upper lobes + TB risk; asbestosis = lower lobes + pleural plaques + mesothelioma.

• Byssinosis = "Monday" chest tightness.

• Adenocarcinoma = commonest and the type in non-smokers.

• Aspiration abscess: dependent segments, anaerobes.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 Silica Settles Up (upper lobes) and Summons TB — silicosis

• 🧠 Asbestos goes to the Abdomen-end (lower lobes) and the pleura — asbestosis

• 🧠 Byssinosis = Blue Monday — byssinosis timing

• 🧠 Adeno for the Abstainers (non-smokers) — adenocarcinoma

• 🧠 Pancoast Pinches the sympathetic chain → Ptosis, Pupil small — Pancoast and Horner

• 🧠 3 months × 2 years = chronic bronchitis — definition

Rapid-Revision Cards

• Commonest pneumonia bug

  S. pneumoniae — all ages, settings, regions.

• Atypical CAP

  Mycoplasma, Chlamydia pneumoniae, Legionella.

• Lung abscess

  Aspiration; anaerobes; dependent segments; air-fluid level.

• Chronic bronchitis

  Cough ≥ 3 months/yr × 2 yr.

• COPD in smokers

  Only ~15%.

• α1-antitrypsin deficiency

  Emphysema + liver disease; non-smokers.

• Asthma cells

  Th2, eosinophils, mast cells.

• Bronchiectasis

  Dilated bronchi; CF, immune defects, PCD.

• AHRF

  PaO2 < 60, P/F < 300, SpO2 < 88%.

• Silicosis

  Upper lobes, eggshell nodes, TB risk.

• Caplan syndrome

  Pneumoconiosis + RA nodules.

• Asbestosis

  Lower lobes, pleural plaques, asbestos bodies.

• Mesothelioma

  Asbestos; latency 30–50 yr.

• Byssinosis

  Cotton/flax/hemp; Monday tightness.

• Berylliosis

  Granulomas like sarcoid.

• Lung cancer and smoking

  ~85%; 15–20% never smoked.

• Commonest lung cancer

  Adenocarcinoma (never-smokers too).

• Pancoast

  Shoulder/arm pain, Horner syndrome.

• Radon

  2nd cause of lung cancer (US).

Sources

Facts in this article were checked against these documents.

• MSD Manual Professional: Pneumonia; Lung Abscess; COPD; Alpha-1 Antitrypsin Deficiency; Asthma; Bronchiectasis; Acute Hypoxemic Respiratory Failure — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• MSD Manual Professional: Silicosis; Coal Worker Pneumoconiosis; Asbestosis; Asbestos-Related Pleural Disease; Mesothelioma; Byssinosis; Beryllium Disease — Merck & Co. (MSD Manuals), reviewed 2026 (link)

• MSD Manual Professional: Lung Carcinoma — Merck & Co. (MSD Manuals), reviewed 2026 (link)

• Competency Based Undergraduate Curriculum, Pathology (PA 25) — National Medical Commission, 2024

Test Yourself: Practice Questions

Thirty questions in NEET PG style, most of them clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. The commonest bacterial cause of pneumonia across all age groups and settings is

• (a) Streptococcus pneumoniae

• (b) Staphylococcus aureus

• (c) Klebsiella

• (d) Pseudomonas

Q2. Which of these is an 'atypical' cause of community-acquired pneumonia?

• (a) Streptococcus pneumoniae

• (b) Escherichia coli

• (c) Haemophilus influenzae

• (d) Mycoplasma pneumoniae

Q3. A patient at risk of aspiration develops a lung cavity with an air-fluid level. The usual organisms and the cause are

• (a) a pulmonary infarct

• (b) fungal infection

• (c) TB reactivation

• (d) anaerobes after aspiration of oral secretions

Q4. An aspiration lung abscess in a recumbent patient typically forms in the

• (a) posterior segments of the upper lobes or superior/lateral basal segments of the lower lobes

• (b) anterior segment of the upper lobe only

• (c) lingula only

• (d) apex only

Q5. Chronic bronchitis is defined clinically as productive cough on most days for at least

• (a) 6 weeks once

• (b) 1 year continuously

• (c) 1 month a year

• (d) 3 months a year for 2 consecutive years

Q6. Of people who smoke, the share who develop clinically apparent COPD is about

• (a) 90%

• (b) 50%

• (c) 15%

• (d) 1%

Q7. A non-smoker has emphysema and liver disease. The likely inherited cause is

• (a) alpha-1 antitrypsin deficiency

• (b) Marfan syndrome

• (c) cystic fibrosis

• (d) Kartagener syndrome

Q8. The cells that drive allergic (T2-high) asthma include

• (a) plasma cells only

• (b) neutrophils only

• (c) NK cells only

• (d) Th2 lymphocytes, eosinophils and mast cells

Q9. A young adult has chronic cough with large amounts of purulent sputum; CT shows dilated, thick-walled bronchi. A common underlying cause is

• (a) asthma

• (b) pulmonary embolism

• (c) cystic fibrosis

• (d) sarcoidosis

Q10. Bronchiectasis can result from a congenital defect in mucociliary clearance called

• (a) alpha-1 antitrypsin deficiency

• (b) surfactant deficiency

• (c) primary ciliary dyskinesia

• (d) sickle cell disease

Q11. Acute hypoxaemic respiratory failure is defined by

• (a) pH < 7.35 only

• (b) PaCO2 > 50 only

• (c) PaO2 < 60 mm Hg, PaO2/FiO2 < 300 or SpO2 < 88%

• (d) SpO2 < 95%

Q12. A worker with years of dust exposure has upper-lobe nodular opacities and eggshell calcification of hilar nodes. The disease and a key complication are

• (a) asbestosis — mesothelioma

• (b) byssinosis — asthma

• (c) berylliosis — sarcoid

• (d) silicosis — increased tuberculosis risk

Q13. Silicosis is caused by inhaling

• (a) respirable crystalline silica

• (b) beryllium fumes

• (c) asbestos fibres

• (d) cotton dust

Q14. A coal miner with rheumatoid arthritis develops multiple lung nodules. This is

• (a) TB

• (b) Caplan syndrome (rheumatoid pneumoconiosis)

• (c) silicosis

• (d) metastatic cancer always

Q15. A worker has bilateral peripheral lower-lobe fibrosis and calcified pleural plaques. The likely exposure is

• (a) asbestos

• (b) cotton

• (c) coal

• (d) silica

Q16. The hallmark of asbestos exposure in the pleura is

• (a) pleural plaques (often calcified)

• (b) pneumothorax

• (c) chylothorax

• (d) empyema

Q17. A man develops a primary pleural cancer decades after occupational mineral-fibre exposure. The tumour and typical latency are

• (a) lymphoma — 5 years

• (b) sarcoma — 6 months

• (c) mesothelioma — 30 to 50 years

• (d) adenocarcinoma — 1 year

Q18. A textile mill worker gets chest tightness that is worst on the first day back at work each week. The diagnosis is

• (a) silicosis

• (b) byssinosis (cotton, flax, hemp dust)

• (c) farmer's lung

• (d) asbestosis

Q19. Chronic beryllium disease is easily confused with

• (a) sarcoidosis (both form granulomas)

• (b) asbestosis

• (c) TB always

• (d) asthma

Q20. The proportion of lung cancers related to cigarette smoking is about

• (a) 25%

• (b) 100%

• (c) 50%

• (d) 85%

Q21. A non-smoking woman develops lung cancer. The most likely histological type is

• (a) large cell carcinoma

• (b) adenocarcinoma

• (c) squamous cell carcinoma

• (d) small cell carcinoma

Q22. A smoker has shoulder and arm pain, hand wasting, ptosis and a small pupil on the same side. The lesion is

• (a) a Pancoast (superior sulcus) tumour with Horner syndrome

• (b) a central squamous carcinoma

• (c) mesothelioma

• (d) a cervical rib only

Q23. After a smoker quits, the risk of lung cancer

• (a) returns to normal within a year

• (b) falls but never returns to that of a never-smoker

• (c) is unchanged

• (d) rises

Q24. A non-occupational radioactive gas that raises lung cancer risk, especially in smokers, is

• (a) radon

• (b) nitrogen

• (c) ozone

• (d) carbon monoxide

Q25. The mutation found in about 91% of lung squamous cell carcinomas is in

• (a) EGFR

• (b) ALK

• (c) KRAS

• (d) TP53

Q26. Lung cancer is first divided histologically into

• (a) primary and secondary only

• (b) small cell and non-small cell

• (c) benign and malignant only

• (d) central and peripheral only

Q27. Which of these is a confirmed lung carcinogen besides tobacco smoke?

• (a) fluoride

• (b) caffeine

• (c) vitamin C

• (d) asbestos

Q28. The disease that is the leading cause of cancer death in men and women worldwide is

• (a) lung carcinoma

• (b) breast cancer

• (c) colon cancer

• (d) prostate cancer

Q29. Coal worker pneumoconiosis at its most severe becomes

• (a) pleural plaques

• (b) bronchiectasis

• (c) progressive massive fibrosis

• (d) mesothelioma

Q30. Asthma pathophysiology includes all of the following EXCEPT

• (a) airway hyperreactivity

• (b) airway remodelling

• (c) bronchoconstriction

• (d) alveolar wall destruction as the main lesion

Active Recall

From memory: name the commonest pneumonia pathogen and the atypicals; describe lung abscess cause and site; define chronic bronchitis and the role of alpha-1 antitrypsin; describe asthma and bronchiectasis; match silica, coal, asbestos, cotton and beryllium to their diseases; and summarise lung cancer risk factors, types, Pancoast tumour and mesothelioma.