Emphysema - Complete Notes for ABVMU 2nd Prof Pathology Exam

DEFINITION

• It is an anatomical diagnosis (unlike chronic bronchitis, which is a clinical diagnosis).
• It is classified by its anatomic distribution within the lobule/acinus.

Remember: The acinus = structure distal to terminal bronchiole (respiratory bronchioles + alveolar ducts + alveoli). A cluster of 3-5 acini = lobule.

CLASSIFICATION / TYPES

1. Centriacinar (Centrilobular) Emphysema - Most Common

• Most common type - >95% of clinically significant cases
• Central/proximal parts of the acinus (respiratory bronchioles) are affected; distal alveoli are spared
• Both normal and emphysematous spaces coexist within the same acinus
• Predominantly affects upper lobes, apical segments
• Strongly associated with cigarette smoking
• Most common form of COPD-related emphysema

2. Panacinar (Panlobular) Emphysema

• Uniform enlargement of the entire acinus - from respiratory bronchiole to terminal alveoli
• Predominantly affects lower lung zones and anterior margins
• Associated with α1-antitrypsin (AAT) deficiency
• Occurs earlier and more severely in smokers with AAT deficiency

3. Distal Acinar (Paraseptal) Emphysema

• Proximal part of acinus is spared; distal part is predominantly involved
• Located near the pleura, lobular septa, and margins adjacent to fibrosis/scarring
• More severe in the upper half of lungs
• Enlarged air spaces 0.5 mm - >2 cm, can form bullae
• Commonly presents as spontaneous pneumothorax in young adults
• Cause is unknown

4. Irregular (Paracicatricial) Emphysema

• Acinus is irregularly involved, almost always associated with scarring
• Usually occurs as small foci and is clinically insignificant

PATHOGENESIS

Step-by-step Mechanism:

• Cigarette smoke + noxious particles damage respiratory epithelium
• Triggers inflammation - releases mediators: LTB4, IL-8, TNF
• Macrophages and epithelial cells recruit neutrophils into the lung

• Neutrophils and macrophages release elastases and other proteases
• These break down elastin and other connective tissue components
• Normally, α1-antitrypsin (α1-AT) inhibits elastase
• When α1-AT is deficient (genetic - Z allele on chromosome 14, Pi locus) OR overwhelmed by smoking, elastin destruction proceeds unchecked
• Loss of elastic tissue → loss of radial traction → airway collapse on expiration → functional airflow obstruction

• Tobacco smoke + inflammatory cells generate oxidants (reactive oxygen species)
• Oxidants cause tissue damage, endothelial dysfunction, amplify inflammation
• NRF2 (encoded by NFE2L2) is a protective transcription factor - inactivation increases susceptibility to smoke damage

• Does NOT initiate emphysema
• But may maintain and acutely exacerbate existing disease

α1-Antitrypsin Deficiency - Important Detail:

• Encoded by Pi locus on chromosome 14
• ~0.01% of US population homozygous for Z allele → markedly decreased serum AAT

• 80% of ZZ individuals develop symptomatic panacinar emphysema

• Worsened significantly by smoking
• About 1% of all emphysema patients have this defect

MORPHOLOGY

Gross Appearance:

• Panacinar emphysema: Pale, voluminous lungs, often overlap the heart anteriorly, diaphragm is flattened
• Centriacinar emphysema: Less impressive grossly; deeper pink, less voluminous; upper 2/3 more severely affected
• Large alveoli visible on cut surface
• Apical blebs or bullae in advanced disease (bullae = spaces >1 cm)

Microscopic Appearance:

• Abnormally large alveolar spaces separated by thin septa
• Destruction of alveolar walls WITHOUT fibrosis (key distinguishing feature)
• Focal centriacinar fibrosis
• Loss of attachments between alveoli and outer wall of small airways
• Pores of Kohn are so enlarged that septa appear to float / protrude blindly into spaces (club-shaped ends)
• Decrease in capillary bed (due to alveolar wall loss)
• Inflammatory changes in small airways (bronchiolar inflammation + submucosal fibrosis) in advanced disease

CLINICAL FEATURES

Pulmonary Function Tests (PFT):

• FEV1/FVC ratio decreased (obstructive pattern)
• Total Lung Capacity (TLC) increased (air trapping)
• Residual Volume (RV) increased
• Diffusing capacity (DLCO) decreased (loss of alveolar surface area)

Complications:

• Pulmonary hypertension → Cor pulmonale (right heart failure)
• Respiratory failure (superimposed infection)
• Spontaneous pneumothorax (rupture of bullae - especially in paraseptal type)
• Secondary polycythemia (chronic hypoxemia)
• Death from respiratory failure or right heart failure

OTHER FORMS OF EMPHYSEMA (Harsh Mohan classifies these separately)

COMPARISON: PINK PUFFER vs BLUE BLOATER (Important Exam Table)

SUMMARY - HIGH-YIELD EXAM POINTS

1. Definition: Permanent enlargement of air spaces DISTAL to terminal bronchioles + wall destruction WITHOUT fibrosis
2. Most common type: Centriacinar (upper lobes, smoking)
3. Alpha-1 antitrypsin deficiency → Panacinar emphysema (lower lobes)
4. Spontaneous pneumothorax in young adults → Paraseptal (distal acinar) emphysema
5. Pathogenesis: Protease-antiprotease imbalance (neutrophil elastase vs α1-AT)
6. Pi locus, chromosome 14 - ZZ genotype = severe AAT deficiency
7. Morphology: Voluminous pale lungs, destroyed alveolar walls, NO fibrosis
8. Pink puffer = thin, pursed lips, severe dyspnea, no cyanosis
9. DLCO decreased (distinguishes from simple asthma)
10. Bullae rupture → Pneumothorax