What are the diagnosis and treatment criteria for Allergic Bronchopulmonary Aspergillosis (ABPA) versus Allergic Bronchopulmonary Mycosis (ABPM)?

Diagnostic Criteria for ABPA vs ABPM

The diagnosis of ABPA requires two essential components (A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹ and serum total IgE ≥500 IU·mL⁻¹) plus at least two additional criteria, while ABPM diagnosis requires normal A. fumigatus-specific IgE but repeated isolation of a non-Aspergillus fungus with evidence of sensitization to that specific fungus. 1, 2

Predisposing Conditions for Both ABPA and ABPM

Both conditions typically occur in patients with:

• Asthma
• Cystic fibrosis
• Chronic obstructive pulmonary disease
• Bronchiectasis
• Or compatible clinico-radiological presentation 1, 2

Diagnostic Criteria for ABPA

Essential Components (both required)

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

Other Components (at least two required)

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

Important Considerations

• High-attenuation mucus on CT is pathognomonic and confirms ABPA diagnosis even if other criteria are not fulfilled
• A positive type 1 skin test is acceptable when Aspergillus-IgE testing is unavailable
• Elevated IgE against recombinant Aspergillus antigens (rAsp f1, f2, and f4) supports ABPA diagnosis 1, 2

Diagnostic Criteria for ABPM

Essential Components

• A. fumigatus-specific IgE <0.35 kUA·L⁻¹
• Repeated isolation of non-Aspergillus fungi (at least two sputum cultures or one bronchoalveolar lavage fluid culture)
• Sensitization to the implicated fungus (skin test or fungus-specific IgE)
• Serum total IgE ≥500 IU·mL⁻¹ 1

Other Components (at least two required)

• Blood eosinophil count ≥500 cells·μL⁻¹
• Positive IgG against the implicated fungus
• Thin-section chest CT consistent with ABPM
• Fleeting opacities on chest radiograph 1

Important Considerations

• Absence of elevated IgE against rAsp f1, f2, and f4 excludes ABPA and supports ABPM diagnosis
• Commercial assays for detecting IgE and IgG against fungi other than Aspergillus are limited to few species (Alternaria, Cladosporium, Candida, Mucor, Trichophyton, and Penicillium) 1

Diagnostic Algorithm

1. Start with A. fumigatus-specific IgE testing
2. If ≥0.35 kUA·L⁻¹, measure serum total IgE
3. If total IgE ≥500 IU·mL⁻¹, proceed with:
   • A. fumigatus-specific IgG testing
   • Peripheral blood eosinophil count
   • Thin-section chest CT
   • Lung function tests 1, 2
4. If A. fumigatus-specific IgE <0.35 kUA·L⁻¹ but clinical suspicion remains, consider ABPM and obtain:
   • Sputum cultures (at least two positive for the same fungus)
   • Specific IgE or skin test for the isolated fungus 1

Radiological Classification of ABPA

The 2024 ISHAM guidelines classify ABPA into five radiological categories:

1. ABPA-S (Serological): ABPA with no bronchiectasis
2. ABPA-B: ABPA with bronchiectasis
3. ABPA-MP: ABPA with mucus plugging but without high-attenuation mucus
4. ABPA-HAM: ABPA with high-attenuation mucus
5. ABPA-CPF: ABPA with chronic pleuropulmonary fibrosis 1, 2

Common Pitfalls and Caveats

• Serum total IgE <500 IU·mL⁻¹ may be acceptable if all other criteria are fulfilled, particularly in patients with prior glucocorticoid treatment, the elderly, or those with constitutively low IgE 1
• High risk of misclassifying ABPA as ABPM if IgE and IgG against Aspergillus are performed using non-standardized assays 1
• Central bronchiectasis on high-resolution CT scan is among the most sensitive and specific diagnostic parameters 3
• In settings where fungus-specific serology is unavailable, ABPM may be pragmatically diagnosed with repeated culture growth, elevated serum total IgE, peripheral blood eosinophilia, and compatible radiological features, provided Aspergillus-specific serology is negative 1
• The prevalence of ABPA/ABPM varies significantly depending on which diagnostic criteria are applied, with rates ranging from 3.0% to 5.5% among patients with persistent allergic asthma 4

Early diagnosis and treatment of ABPA/ABPM is crucial to prevent progression to irreversible lung fibrosis and should be considered in all patients with asthma and fungal sensitization 3.