Acute Dyspnea

Christopher M. Walker, MD

DIFFERENTIAL DIAGNOSIS

Common

Pneumonia
Pulmonary Edema
Pulmonary Embolism
Pneumothorax
Pleural Effusion
Aspiration
Asthma/COPD Exacerbation

Less Common

Lobar Collapse
Septic Embolism
Pericardial Disease

Rare but Important

Acute Interstitial Pneumonia
Pulmonary Hemorrhage
Fat Embolism
Interstitial Lung Disease Exacerbation
Acute Hypersensitivity Pneumonitis
Acute Eosinophilic Pneumonia

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Review focuses on intrathoracic causes of dyspnea presenting within minutes to days

Helpful Clues for Common Diagnoses

Pneumonia
- Symptoms of infection
- Lobar or segmental lung consolidation
- ± pleural effusion
Pulmonary Edema
- Pulmonary venous hypertension with transudation of fluid
- Radiographs and CT
  - Smooth interlobular septal thickening (Kerley B lines)
  - Fissural thickening
  - Dependent distribution
  - ± pleural effusions
Pulmonary Embolism
- CTA: Filling defect is diagnostic
  - “Railroad track” or “doughnut” signs
- Document signs of right heart strain
  - RV/LV chamber size ≥1, reflux of contrast into IVC, or leftward bowing of interventricular septum
Pneumothorax
- Spontaneous
  - Rupture of apical bleb or bulla
  - Young, tall, and thin male smokers
  - Association with emphysema, asthma, infection, lung fibrosis, or cystic lung disease
  - Recurs in 50% of patients
- Traumatic
  - Chest trauma or mechanical ventilation
Pleural Effusion
- Exudative effusions
  - Causes include infections, malignancy, connective tissue diseases, and asbestos exposure
  - Pleural thickening and enhancement seen in 60%
  - Ultrasound depicts septations and heterogeneous echotexture
- Transudative effusions
  - Common in congestive heart failure, renal disease, and hypoalbuminemia
Aspiration
- Most common in right lower lobe
  - Secondary to more vertical orientation of right mainstem bronchus
- Pleural effusion is uncommon
Asthma/COPD Exacerbation
- Flat diaphragms from lung hyperinflation
- Exacerbation usually does not cause new radiographic findings
- Associated complications
  - Pneumonia
  - Pneumothorax
  - Pneumomediastinum
  - Atelectasis

Helpful Clues for Less Common Diagnoses

Lobar Collapse
- Signs of volume loss
  - Mediastinal shift
  - Fissural displacement
  - Crowding of vessels
  - Diaphragmatic elevation
- Occurs secondary to
  - Central obstructing mass or nodule in outpatients
  - Mucus plug in inpatients
Septic Embolism
- Multiple bilateral lower lobe predominant peripheral nodules
- ± central cavitation
- Most common in intravenous drug abusers
Pericardial Disease
- Pericardial effusion
  - Rapid fluid accumulation secondary to malignancy or infection
- Acute pericarditis
  - Pericardial thickening ≥4 mm ± pericardial effusion
  - Contrast enhancement of thickened pericardium

Helpful Clues for Rare Diagnoses

Acute Interstitial Pneumonia
- Acute respiratory distress syndrome without identifiable cause
- Viral respiratory syndrome followed by rapid respiratory decline
- Bilateral patchy lung consolidation and ground-glass opacity
- Most commonly affects dependent lung
- 50% mortality
Pulmonary Hemorrhage
- Ground-glass opacity or patchy/diffuse consolidation
- ± sparing of subpleural lung
- Pleural effusions are rare
- Important historical clue is presence of hemoptysis or anemia
- Causes
  - Pulmonary-renal syndromes, vasculitis, anticoagulation, drug reactions, and collagen vascular disease
Fat Embolism
- Usually secondary to long bone fracture
- Classic clinical triad
  - Petechial rash, altered mental status, and hypoxia
- Small centrilobular and subpleural lung nodules
- Nonspecific bilateral ground-glass opacity without zonal predominance
Interstitial Lung Disease Exacerbation
- Rapid deterioration in presence of known interstitial lung disease
- Must exclude infection (Pneumocystis) and congestive heart failure
- Ground-glass opacity or consolidation superimposed on interstitial lung disease pattern
Acute Hypersensitivity Pneumonitis
- Occurs with large inhaled antigen exposure
- Middle and lower lung consolidation secondary to acute lung injury
- ± centrilobular nodules of ground-glass opacity
- ± mosaic perfusion and expiratory air-trapping
Acute Eosinophilic Pneumonia
- Fever with rapidly progressing respiratory distress
- Eosinophils in serum and lavage fluid
- Rapid response to steroids
- Radiographic progression similar to pulmonary edema
  - Bilateral reticular opacities and Kerley B lines
  - Lower lobe consolidation, small pleural effusions

Image Gallery

Frontal radiograph shows right mid and lower lung consolidation

in this patient with a high fever and productive cough. Silhouetting of right hemidiaphragm indicates right lower lobe involvement.

Frontal radiograph shows bilateral mid and lower lung consolidation

in this patient presenting with severe hypoxia. Pneumocystis pneumonia and HIV were subsequently diagnosed.

(Left) Frontal radiograph shows multiple lower lobe septal lines or Kerley B lines

, which represent thickening of interlobular septa. Note vascular indistinctness without alveolar filling. (Right) Axial CECT shows dependent ground-glass opacity