What are the clinical features of Allergic Bronchopulmonary Aspergillosis (ABPA)?

Clinical Features of Allergic Bronchopulmonary Aspergillosis (ABPA)

Allergic bronchopulmonary aspergillosis (ABPA) presents with a characteristic constellation of clinical, radiological, and immunological features resulting from hypersensitivity reactions to Aspergillus fumigatus colonizing the airways.

Key Clinical Manifestations

• Respiratory Symptoms:

  • Chronic cough with expectoration of brownish mucus plugs 1
  • Wheezing and dyspnea due to poorly controlled asthma 1
  • Hemoptysis 2
  • Sustained clinical worsening (≥14 days) during exacerbations 3

• Systemic Manifestations:

  • Fever
  • Malaise
  • Weight loss 2

Radiological Features

ABPA can be radiologically classified into five categories 3:

1. ABPA-S (Serological): ABPA without bronchiectasis
2. ABPA-B (Bronchiectasis): ABPA with bronchiectasis
3. ABPA-MP (Mucus Plugging): ABPA with non-hyperattenuating mucus plugs
4. ABPA-HAM (High Attenuation Mucus): ABPA with hyperattenuated mucus
5. ABPA-CPF (Chronic Pleuropulmonary Fibrosis): Advanced fibrotic lung disease

Characteristic Imaging Findings:

• Central bronchiectasis (usually bilateral) - a pathognomonic feature 3
• Mucoid impaction - occurs in up to 20% of patients; can be hyperdense (HAM) or hypodense 2
• Fleeting pulmonary infiltrates 1
• Centrilobular nodules with tree-in-bud appearance 3
• Atelectasis and consolidation 3
• Mosaic attenuation 3

Immunological Features

• Elevated serum total IgE (typically >1000 IU/mL)
• Elevated Aspergillus-specific IgE and IgG antibodies
• Peripheral blood eosinophilia 4
• During exacerbations: increase in serum total IgE by ≥50% from baseline 3

Clinical Classification

According to the revised ISHAM-ABPA working group guidelines, ABPA can be classified into 3:

1. Acute ABPA:

   • Newly diagnosed: Previously undiagnosed ABPA meeting diagnostic criteria
   • Exacerbation: Clinical or radiological worsening with ≥50% increase in IgE

2. Response:

   • ≥50% symptomatic improvement

   • 50% reduction in radiological opacities or ≥20% decline in serum IgE after 8 weeks

3. Remission:

   • Sustained (≥6 months) clinico-radiological improvement off glucocorticoids
   • No rise in serum IgE by ≥50%

4. Treatment-dependent ABPA:

   • Two or more consecutive exacerbations within 3 months of stopping glucocorticoids
   • Worsening symptoms with imaging deterioration or IgE rise within 4 weeks of tapering steroids

5. Advanced ABPA:

   • Extensive bronchiectasis (≥10 segments)
   • Cor pulmonale or chronic type 2 respiratory failure

Differential Diagnosis

It's important to distinguish ABPA exacerbations from:

1. Asthma exacerbations: Worsening respiratory symptoms for ≥48 hours without immunological or radiological deterioration 3

2. Infective/bronchiectasis exacerbations: Clinical deterioration for ≥48 hours with increased cough, breathlessness, sputum volume/consistency, purulence, fatigue, malaise, fever, or hemoptysis, without immunological or radiological deterioration 3

Special Considerations

• In children: CT scans should be ordered with consideration for radiation dosage 3
• Prognostic factors: Extent of bronchiectasis, HAM, and fungal ball are independent predictors of recurrent ABPA exacerbations 3
• Complications: If left untreated, ABPA can progress to irreversible bronchiectasis, chronic pulmonary aspergillosis, and fibrotic lung disease 5, 4

Understanding these clinical features is crucial for early diagnosis and appropriate management to prevent long-term complications and improve quality of life in patients with ABPA.