What is the most likely diagnosis in a patient with asthma, recurrent wheezing, elevated total serum IgE >1000 IU/mL, Aspergillus-specific IgE positivity, eosinophilia, and central bronchiectasis with mucus plugging?

Allergic Bronchopulmonary Aspergillosis (ABPA)

The most likely diagnosis is Allergic Bronchopulmonary Aspergillosis (ABPA), specifically ABPA with mucus plugging (ABPA-MP) and bronchiectasis (ABPA-B). This patient fulfills all essential and additional diagnostic criteria according to the 2024 revised ISHAM-ABPA working group consensus guidelines 1.

Diagnostic Reasoning

This patient meets the revised 2024 ISHAM-ABPA diagnostic criteria 1:

Essential Components (Both Present):

• Aspergillus-specific IgE positivity (≥0.35 kUA·L⁻¹)
• Total serum IgE >1000 IU/mL (far exceeding the required ≥500 IU·mL⁻¹ threshold)

Additional Components (More Than Two Present):

• Eosinophilia (≥500 cells·μL⁻¹)
• CT findings consistent with ABPA: Central bronchiectasis with mucus plugging
• Predisposing condition: Asthma with recurrent wheezing

The markedly elevated total IgE (>1000 IU/mL) is particularly significant—while the diagnostic threshold is ≥500 IU/mL, levels exceeding 1000 IU/mL strongly support ABPA diagnosis 1. The combination of central bronchiectasis with mucus plugging is highly characteristic of ABPA and distinguishes it from simple Aspergillus sensitization in asthma 1.

Clinical Classification

Based on imaging findings, this patient has:

• ABPA-B (ABPA with bronchiectasis)
• ABPA-MP (ABPA with mucus plugging)

If high-attenuation mucus (HAM) is visible on CT, this would be pathognomonic for ABPA and confirms the diagnosis even if other criteria were incomplete 1. HAM appears as hyperdense mucus plugs on CT imaging and represents inspissated mucus with high protein and mineral content 2.

Key Diagnostic Pitfalls to Avoid

Do not confuse ABPA with:

1. Severe asthma with fungal sensitization: These patients have Aspergillus-specific IgE but lack the additional criteria (bronchiectasis, mucus plugging, markedly elevated total IgE >500 IU/mL) 1

2. Aspergillus bronchitis: May show positive respiratory cultures and elevated Aspergillus-IgG with bronchiectasis, but lacks the immunological profile (markedly elevated total IgE and Aspergillus-specific IgE) 1

3. Chronic pulmonary aspergillosis: Can have elevated Aspergillus-IgE and total IgE, but typically presents with cavitary disease rather than central bronchiectasis with mucus plugging 1

4. Allergic Bronchopulmonary Mycosis (ABPM): Would require Aspergillus-specific IgE <0.35 kUA·L⁻¹ with sensitization to a different fungus and repeated fungal cultures growing the causative organism 1

Additional Workup Considerations

While the diagnosis is established, consider:

• Aspergillus-specific IgG testing: Provides additional diagnostic support (though not essential when other criteria are met) 1
• Recombinant Aspergillus antigens (rAsp f1, f2, f4): Elevated levels further support ABPA diagnosis and can be used as an additional diagnostic component 1
• Exclude other causes of bronchiectasis: Complete blood count, immunoglobulin levels, sweat chloride test (to exclude cystic fibrosis), and mycobacterial cultures, particularly in patients with extensive bronchiectasis 1

Important Clinical Context

The 2024 ISHAM guidelines 1 represent the most current, evidence-based diagnostic framework, superseding the 2013 criteria and incorporating advances in serological testing. The guidelines emphasize that serum total IgE ≥500 IU/mL is more sensitive than the previously used 1000 IU/mL threshold 1, though this patient exceeds even the higher threshold.

The presence of central bronchiectasis (typically involving proximal airways) with mucus plugging is a hallmark radiological pattern that distinguishes ABPA from other forms of bronchiectasis, which typically affect peripheral airways 1, 3. This pattern reflects the immune-mediated airway damage caused by chronic hypersensitivity to Aspergillus antigens colonizing the bronchial mucus 4, 5.