A 58-year-old male smoker with 40 pack-year history presents with progressive dyspnea and a DLCO of 45% predicted. On histology, there is loss of alveolar walls predominantly in the upper lung lobes with sparing of the lower lobes. Which feature best distinguishes this type of emphysema from panacinar emphysema?

Question

Accepted Answer

D. Selective destruction of distal alveoli (respiratory bronchioles) with sparing of proximal alveoli (terminal bronchioles). ## Centrilobular vs. Panacinar Emphysema

### Clinical Presentation Analysis

The vignette describes:
- **Upper lobe predominance** (classic for centrilobular)
- **Smoking history** (strong risk factor for centrilobular)
- **Sparing of lower lobes** (distinguishes from panacinar)

This is **centrilobular emphysema**.

### Comparative Pathology of Emphysema Subtypes

| Feature | Centrilobular | Panacinar |
|---------|---------------|----------|
| **Anatomical pattern** | Proximal alveoli (terminal bronchioles) destroyed; distal alveoli (respiratory bronchioles) spared | Uniform destruction throughout acinus |
| **Lobe distribution** | Upper lobes > lower lobes | Uniform; lower lobes often more severe |
| **Associated risk** | Smoking (heavy smokers) | α1-antitrypsin deficiency |
| **Age of onset** | Middle-aged to older | Younger (30–40 years if homozygous) |
| **Severity** | Often mild to moderate | Often severe and progressive |
| **Histology** | Patchy, irregular destruction | Diffuse, homogeneous destruction |

### Key Discriminating Feature

**Key Point:** The **selective destruction of proximal alveoli (respiratory bronchioles) with sparing of distal alveoli (terminal bronchioles)** is the pathognomonic feature of centrilobular emphysema. "Centrilobular" refers to the **central (proximal) part of the acinus** being affected.

**High-Yield:** Remember the anatomical hierarchy:
- **Terminal bronchiole** (end of conducting airways)
- **Respiratory bronchiole** (first gas-exchanging unit; has alveoli budding from its walls)
- **Alveolar duct** (wall entirely lined with alveoli)
- **Alveolus** (individual air sac)

In centrilobular emphysema, the **respiratory bronchioles are destroyed**, but the **distal alveolar ducts and alveoli are preserved**.

### Pathogenesis

**Clinical Pearl:** Centrilobular emphysema occurs because:
1. Smoking causes oxidative stress and inflammation in **proximal airways**
2. Respiratory bronchioles are more exposed to irritants (they are the first gas-exchanging units)
3. Distal alveoli are relatively protected
4. Results in **upper lobe predominance** (where ventilation is greatest in smokers)

Panacinar emphysema (α1-antitrypsin deficiency) affects all alveoli equally because the protease-antiprotease imbalance is systemic.

### Mnemonic

**Mnemonic: "CUPS"**
- **C**entrilobular = **C**entral (proximal) destruction
- **U**pper lobes
- **P**roximal alveoli destroyed
- **S**moking-related

[cite:Robbins 10e Ch 15]

Answer

A. Uniform destruction of alveoli throughout the acinus from proximal to distal

Answer

B. Association with α1-antitrypsin deficiency and early-onset disease

Answer

C. Predominant involvement of lower lobes with basilar distribution

Explanation

Centrilobular vs. Panacinar Emphysema

Clinical Presentation Analysis

Comparative Pathology of Emphysema Subtypes

Key Discriminating Feature

Pathogenesis

Mnemonic

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Feature	Centrilobular	Panacinar
Anatomical pattern	Proximal alveoli (terminal bronchioles) destroyed; distal alveoli (respiratory bronchioles) spared	Uniform destruction throughout acinus
Lobe distribution	Upper lobes > lower lobes	Uniform; lower lobes often more severe
Associated risk	Smoking (heavy smokers)	α1-antitrypsin deficiency
Age of onset	Middle-aged to older	Younger (30–40 years if homozygous)
Severity	Often mild to moderate	Often severe and progressive
Histology	Patchy, irregular destruction	Diffuse, homogeneous destruction