When should Allergic Bronchopulmonary Aspergillosis (ABPA) be suspected in patients with asthma or cystic fibrosis, according to International Society for Human and Animal Mycology (ISHAM) guidelines?

When to Suspect Allergic Bronchopulmonary Aspergillosis (ABPA) and Predisposing Conditions

According to the 2024 ISHAM guidelines, ABPA should be suspected in patients with predisposing conditions (asthma, cystic fibrosis, chronic obstructive lung disease, bronchiectasis) or those with a compatible clinico-radiological presentation such as expectoration of mucus plugs, fleeting opacities on chest imaging, finger-in-glove opacities, and lung collapse. 1

Predisposing Conditions

The primary predisposing conditions for ABPA include:

1. Asthma - Most common predisposing condition

   • ABPA is present in 7-14% of corticosteroid-dependent asthmatic patients 1
   • Screening is recommended for all newly diagnosed asthmatic adults at tertiary care centers 1
   • For children, screening is only recommended in difficult-to-treat asthma cases 1

2. Cystic Fibrosis (CF)

   • Approximately 7% of CF patients develop ABPA 1
   • CF patients are at particular risk for invasive aspergillosis if lung transplantation is performed 1

3. Chronic Obstructive Pulmonary Disease (COPD)

   • Less common but recognized as a predisposing condition 1, 2
   • Studies have found Aspergillus hypersensitivity in 8.5% of COPD patients 3

4. Bronchiectasis (non-CF)

   • Can both predispose to and result from ABPA 1, 2

Clinical Presentations That Should Raise Suspicion

ABPA should be suspected when patients with predisposing conditions present with:

1. Respiratory symptoms:

   • Wheezing (episodic bronchial obstruction)
   • Dyspnea
   • Cough
   • Expectoration of brown mucus plugs or flecks

2. Radiological findings:

   • Fleeting pulmonary infiltrates/opacities (transient areas of consolidation)
   • Central bronchiectasis (usually bilateral)
   • Mucus plugging (may form band shadows or glove-finger shadows)
   • High-attenuation mucus (pathognomonic of ABPA)
   • "Ring sign" or "tram lines" (parallel shadows representing inflamed bronchi)
   • Finger-in-glove opacities
   • Lung collapse

3. Laboratory abnormalities:

   • Peripheral blood eosinophilia (≥500 cells/μL)
   • Elevated serum total IgE (≥500 IU/mL)
   • Positive Aspergillus fumigatus-specific IgE (≥0.35 kUA/L)
   • Positive IgG against Aspergillus fumigatus

Screening Recommendations

The 2024 ISHAM guidelines recommend:

• For adults: Screen all newly diagnosed asthmatic patients at tertiary care centers for Aspergillus fumigatus sensitization using fungus-specific IgE 1
• For children: Screen only difficult-to-treat asthmatic children 1
• For CF patients: Regular screening is implied but specific intervals are not stated in the guidelines 1, 4

Diagnostic Criteria

According to the revised 2024 ISHAM-ABPA working group consensus criteria, ABPA diagnosis requires:

1. Predisposing conditions or compatible clinico-radiological presentation
2. Essential components:
   • A. fumigatus-specific IgE ≥0.35 kUA/L
   • Serum total IgE ≥500 IU/mL
3. Plus any two of the following:
   • Positive IgG against A. fumigatus
   • Blood eosinophil count ≥500 cells/μL
   • Chest CT findings consistent with ABPA or fleeting opacities on chest radiograph 1

Clinical Pearls and Pitfalls

• High-attenuation mucus is pathognomonic of ABPA and confirms the diagnosis even if all other criteria are not fulfilled 1
• Isolated central bronchiectasis is encountered in few conditions, including ABPA and tracheobronchomegaly, making it a helpful distinguishing feature 1
• Differential diagnosis should include chronic eosinophilic pneumonia, Churg-Strauss syndrome, drug-induced pulmonary infiltrates, parasitic infections, atelectasis in asthma, and lymphoma 5
• Early identification and treatment of ABPA is crucial to prevent the progression of bronchiectasis 1
• ABPA can occasionally occur in the absence of any predisposing condition, though this is rare 1
• In patients with COPD, the clinical significance of Aspergillus hypersensitivity and ABPA remains unclear but should be considered 3

By maintaining a high index of suspicion in patients with predisposing conditions and recognizing the characteristic clinical and radiological features, clinicians can diagnose ABPA early and initiate appropriate treatment to prevent irreversible lung damage.