What are the diagnostic criteria and treatment options for Allergic Bronchopulmonary Aspergillosis (ABPA)?

Diagnostic Criteria for Allergic Bronchopulmonary Aspergillosis (ABPA)

The diagnosis of ABPA requires meeting the revised ISHAM-ABPA working group consensus criteria, which include predisposing conditions, essential components, and additional criteria. 1

Predisposing Conditions

• Presence of asthma, cystic fibrosis, chronic obstructive lung disease, bronchiectasis, or a compatible clinico-radiological presentation 1, 2

Essential Components (both required)

• A. fumigatus-specific IgE ≥0.35 kUA·L−1 1
• Serum total IgE ≥500 IU·mL−1 1, 2

Other Components (any two required)

• Positive IgG against A. fumigatus 1
• Blood eosinophil count ≥500 cells·μL−1 (could be historical) 1
• Thin-section chest CT consistent with ABPA (bronchiectasis, mucus plugging and high-attenuation mucus) or fleeting opacities on chest radiograph consistent with ABPA 1, 3

Important Diagnostic Considerations

• High-attenuation mucus (HAM) is pathognomonic of ABPA and confirms diagnosis even if all other criteria are not fulfilled 1, 2, 4
• A positive type 1 skin test is acceptable when Aspergillus-specific IgE testing is unavailable 1, 2
• Serum total IgE <500 IU·mL−1 may be acceptable if all other criteria are fulfilled 1, 2
• Elevated IgE against rAsp f1, f2, and f4 supports the diagnosis and can be used as another component 1, 2

Diagnostic Workup Algorithm

1. Initial Screening: In patients with asthma or other predisposing conditions, perform skin prick testing for Aspergillus fumigatus 5

2. Laboratory Testing: For positive skin test or suspected cases, order:

   • Serum total IgE (cutoff ≥500 IU·mL−1) 1
   • A. fumigatus-specific IgE (cutoff ≥0.35 kUA·L−1) 1
   • A. fumigatus-specific IgG (using population-specific cutoffs when available) 1
   • Peripheral blood eosinophil count (cutoff ≥500 cells·μL−1) 1

3. Imaging Studies:

   • Thin-section chest CT is recommended at baseline to identify bronchiectasis, mucus plugging, HAM, and other abnormalities 1, 3
   • Chest radiograph can be used to assess treatment response but is less sensitive for initial diagnosis 1, 4

4. Additional Testing:

   • Sputum fungal culture is suggested during evaluation of ABPA (not required for diagnosis but may help identify species or guide therapy) 1
   • Serum galactomannan is NOT recommended for diagnosing ABPA 1
   • Bronchoscopy is NOT routinely recommended for diagnosis 1

Radiological Classification

ABPA can be radiologically classified into five categories 1:

• ABPA-S (Serological): ABPA with no bronchiectasis 1, 4
• ABPA-B: ABPA with radiological evidence of bronchiectasis 1, 4
• ABPA-MP: ABPA with mucus plugging but without high-attenuation mucus 1
• ABPA-HAM: ABPA with high-attenuation mucus 1, 4
• ABPA-CPF: ABPA with chronic pleuropulmonary fibrosis 1

Clinical Classification

• Acute ABPA: Newly diagnosed or exacerbation (clinical worsening with ≥50% increase in serum total IgE) 1, 2
• Response: Symptomatic improvement by at least 50% and major radiological improvement or decline in serum total IgE by at least 20% after 8 weeks of treatment 1
• Remission: Sustained clinico-radiological improvement off glucocorticoids 1, 2
• Treatment-dependent ABPA: Two or more consecutive exacerbations within 3 months of stopping glucocorticoids 1
• Advanced ABPA: Extensive bronchiectasis due to ABPA with cor pulmonale or chronic type 2 respiratory failure 1

Common Pitfalls and Caveats

• Relying solely on chest radiographs can miss the diagnosis as findings are often nonspecific 3, 4
• HRCT can be normal in approximately one-third of patients (ABPA-S) 4, 6
• Central bronchiectasis was historically considered specific for ABPA, but peripheral bronchiectasis can also be present in up to 40% of affected lobes 4
• Failure to recognize ABPA early can lead to recurrent pulmonary infiltrates, progressive bronchiectasis, and eventually fibrosis 7, 6
• Differential diagnosis includes chronic eosinophilic pneumonia, Churg-Strauss syndrome, hyper-IgE syndrome, and parasitic infections 6