Give a comprehensive, guideline‑based overview of the diagnosis and management of allergic bronchopulmonary aspergillosis (ABPA) as of October 2023.

Comprehensive Overview of Allergic Bronchopulmonary Aspergillosis (ABPA)

1. Definition and Epidemiology

ABPA is a complex pulmonary disorder caused by an exaggerated type-2 immune response to Aspergillus fumigatus colonizing the airways of patients with underlying chronic lung disease, most commonly asthma or cystic fibrosis. 1

• ABPA represents an asthma endotype and a treatable trait in both CF and non-CF bronchiectasis 1
• The condition occurs in approximately 7–9% of patients with cystic fibrosis 2
• ABPA may occasionally develop in patients with bronchiectasis, COPD, or even in the absence of any predisposing condition 1
• The fungus grows within the airways without invading lung tissue, distinguishing it from invasive aspergillosis 2

2. Etiology

The pathophysiology centers on chronic airway colonization by A. fumigatus triggering a genetically determined hypersensitivity reaction in susceptible hosts. 3

• Aspergillus fumigatus is the causative organism in classic ABPA; other fungi cause allergic bronchopulmonary mycosis (ABPM) 1
• The fungus persists in airways due to host factors that permit colonization combined with an exaggerated immune response 3
• Type-2 immune mechanisms drive persistent inflammation and progressive tissue damage 4
• The interaction between fungal antigens and host immunity generates the clinical syndrome through IgE-mediated and IgG-mediated pathways 5

3. Clinical Presentation

Patients present with poorly controlled asthma characterized by recurrent wheezing, chronic cough, dyspnea, and expectoration of brownish mucus plugs. 4

Acute Manifestations

• Episodic wheezing and bronchial obstruction 6
• Cough with expectoration of brown plugs or flecks (characteristic) 6
• Breathlessness and chest tightness 6
• Pyrexia, fatigue, and malaise 6
• Recurrent pulmonary infiltrates on imaging 4

Chronic Manifestations

• Progressive bronchiectasis (central, bilateral, upper/middle lobe predominant) 1
• Mucus plugging and impaction 4
• In advanced ABPA-CPF: pulmonary fibrosis, fibro-cavitary lesions, fungal balls, and pleural thickening 2
• End-stage fibrotic lung disease in untreated cases 5

4. Diagnostic Criteria

The 2024 ISHAM-ABPA Working Group criteria require: (1) a predisposing condition or compatible presentation, (2) mandatory demonstration of A. fumigatus sensitization, (3) serum total IgE ≥500 IU/mL, and (4) two additional criteria from: A. fumigatus-specific IgG, peripheral eosinophilia, or suggestive imaging. 1

Mandatory Criteria

• Serum total IgE ≥500 IU/mL (lowered from previous 1000 IU/mL threshold for improved sensitivity) 1
• Elevated A. fumigatus-specific IgE (mandatory; superior to skin testing) 1

Additional Criteria (Two Required)

• Elevated A. fumigatus-specific IgG by enzyme immunoassay (superior to immunoprecipitation) 1
• Peripheral blood eosinophilia 1
• Suggestive imaging findings 1

Imaging Investigations

• High-resolution CT (HRCT) with 1.25–1.5 mm thin sections and IV contrast is the gold standard 6
• Central bronchiectasis (bilateral, upper/middle lobe predominant) in 63–89% of cases 6
• High-attenuation mucus (HAM) has 100% specificity and is pathognomonic—when present, confirms ABPA diagnosis even if other criteria incomplete 6
• HAM detected in 35–36% of patients; must be evaluated on mediastinal windows 6
• Mucoid impaction in 59–86% of cases 6
• Centrilobular nodules with tree-in-bud pattern in 86% 6
• Consolidation in 17–43% (often mucus-filled bronchiectatic cavities) 6

Laboratory Tests

• Serum total IgE measurement 1
• A. fumigatus-specific IgE assay (preferred over skin testing) 1
• A. fumigatus-specific IgG by enzyme immunoassay 1
• Lateral flow assay for A. fumigatus-IgG now available 1
• Complete blood count for eosinophilia 1

Radiological Classification (2024 ISHAM)

• ABPA-S (Serological): No bronchiectasis 6
• ABPA-B (Bronchiectasis): Bronchiectasis present 6
• ABPA-MP (Mucus Plugging): Mucus plugs without HAM 6
• ABPA-HAM: High-attenuation mucus identified (pathognomonic) 6
• ABPA-CPF: Two or more features of chronic pleuropulmonary fibrosis (fibrosis, fibro-cavitary lesions, fungal ball, pleural thickening) 6

5. Differential Diagnosis

Chronic pulmonary aspergillosis (CPA) is the most critical differential, distinguished by predominant Aspergillus-specific IgG elevation without marked IgE elevation, absence of eosinophilia, and progressive cavity formation rather than central bronchiectasis. 2

Key Differentials and Distinguishing Features

Chronic Pulmonary Aspergillosis (CPA)

• CPA shows Aspergillus-specific IgG positive in >90% but total IgE not markedly elevated 2
• CPA lacks eosinophilia (present in ABPA) 2
• CPA demonstrates progressive cavity formation with aspergilloma, cavity wall thickening, and air-crescent sign 2
• CPA occurs in pre-existing lung cavities from TB, COPD, or structural disease 2
• Pitfall: ABPA-CPF can mimic CPA; compare immunologic profiles—dominant IgE + eosinophilia favors ABPA 2

Pulmonary Tuberculosis

• Fleeting infiltrates in ABPA often confused with TB 5
• TB shows acid-fast bacilli on sputum, positive cultures, and different radiographic patterns 5

Severe Asthma Without ABPA

• Lacks elevated total IgE ≥500 IU/mL 1
• Absent A. fumigatus sensitization 1
• No central bronchiectasis or HAM on imaging 6

Eosinophilic Granulomatosis with Polyangiitis (EGPA)

• Systemic vasculitis features (sinusitis, neuropathy, cardiac involvement) 4
• ANCA positivity in subset of patients 4
• Peripheral eosinophilia present but different imaging pattern 4

Non-CF Bronchiectasis with Aspergillus Colonization

• Bronchiectasis present but not central distribution 1
• May have Aspergillus growth but lacks marked IgE elevation 1
• Aspergillus bronchitis without hypersensitivity features 1

Cystic Fibrosis Exacerbation

• Bronchiectasis and mucus plugging occur independently of ABPA in CF 1
• Requires fulfillment of ABPA immunologic criteria to distinguish 1

6. Management and Treatment

For newly diagnosed or infrequently relapsing ABPA, monotherapy with either oral prednisolone 0.5 mg/kg/day for 2 weeks followed by 8–12 week taper OR oral itraconazole 200 mg twice daily for 6 months with therapeutic drug monitoring is recommended as first-line treatment. 7

Acute ABPA (Newly Diagnosed or Infrequent Exacerbations)

Monotherapy Options (choose one):

• Oral prednisolone: 0.5 mg/kg/day for 2 weeks, then taper over 8–12 weeks 7

  • Clears pulmonary infiltrates and reduces immunologic activity 7
  • Monitor for diabetes, weight gain, and bone mineral density loss 7

• Oral itraconazole: 200 mg twice daily for 6 months 7

  • Therapeutic drug monitoring mandatory to ensure adequate serum levels 7
  • Alternative azoles (voriconazole, posaconazole) if itraconazole unsuitable 7

Recurrent ABPA Exacerbations (≥2 Episodes in 1–2 Years)

Combination therapy with oral prednisolone PLUS oral itraconazole is recommended for recurrent exacerbations, especially with extensive bronchiectasis. 7

• This represents 71% expert consensus from 2024 ISHAM guidelines 7
• Reserve combination for recurrent cases; do not use for all newly diagnosed ABPA 7

Asymptomatic ABPA

Do not treat asymptomatic ABPA even when serological criteria are fulfilled; initiate therapy only when clinical symptoms develop. 7

• This avoids unnecessary corticosteroid exposure 7

Refractory Disease

• Pulse intravenous methylprednisolone for exacerbations unresponsive to oral glucocorticoids (limited evidence) 7
• Biologic agents (anti-IL-5, anti-IgE such as omalizumab) for steroid-dependent or refractory disease 2

Therapies NOT Recommended

• Biologic agents for acute exacerbations (94.3% consensus against) 7
• Nebulized amphotericin B (100% consensus against; poor efficacy) 7
• High-dose inhaled corticosteroids as primary therapy (100% consensus against) 7

Management in Concomitant Conditions

Asthma with ABPA:

• Follow monotherapy or combination protocols above based on exacerbation frequency 7
• Optimize asthma control with inhaled corticosteroids and bronchodilators as baseline 4
• Screen all newly diagnosed adult asthmatics at tertiary centers for A. fumigatus sensitization 1
• Screen difficult-to-treat asthmatic children for ABPA 1

Cystic Fibrosis with ABPA:

• Apply same diagnostic criteria (total IgE ≥500 IU/mL, A. fumigatus-specific IgE, plus two additional criteria) 1
• Diagnosis more challenging due to baseline bronchiectasis and mucus plugging 1
• Approximately 7% of CF patients develop ABPA 2
• Treatment follows same monotherapy/combination algorithm 7

Environmental Exposure Mitigation

• Minimize inhalation of Aspergillus spores by avoiding soil work and handling decaying vegetation 7
• Use N95 respirators (not surgical masks) when exposure unavoidable 7
• Regular HVAC maintenance, prompt water leak repair, adequate ventilation, and damp-cloth cleaning to reduce indoor spore burden 7

7. Monitoring and Follow-Up

Treatment response should be assessed at 8–12 weeks using a multidimensional criterion incorporating clinical symptoms, serum total IgE, chest imaging, and spirometry. 7

Monitoring Treatment Response (8–12 Weeks)

Objective Response Criteria:

• Clinical symptoms: ≥50% improvement on semiquantitative Likert scale indicates good response 7
• Serum total IgE: ≥20% reduction from baseline (most objective biomarker) 7
• Chest imaging: Resolution of infiltrates and mucus plugging on radiograph or CT 7
• Spirometry: FEV₁ increase ≥158 mL represents minimal clinically important difference 7
• Blood eosinophil count: NOT validated for response assessment; do not rely upon 7

Routine Follow-Up Imaging

Use chest radiographs, not CT, for routine treatment monitoring to minimize cumulative radiation exposure. 6

• Reserve repeat HRCT for: new hemoptysis, suspected treatment failure, or marked clinical deterioration 6
• Low-dose CT protocols may be employed when HRCT necessary for follow-up 6

Defining ABPA Recurrence

ABPA recurrence requires simultaneous presence of: (1) sustained worsening respiratory symptoms, (2) new pulmonary infiltrates, and (3) serum total IgE rise ≥50% above post-treatment baseline for ≥2 weeks. 7

Differentiation from Other Exacerbations

• Asthma-only exacerbation: No IgE elevation ≥50%, no new infiltrates; treat with short-course oral glucocorticoid alone 7
• Infective bronchiectasis exacerbation: No IgE elevation ≥50%, positive sputum cultures; treat with targeted antibiotics 7

Long-Term Monitoring

• Approximately 50% of patients experience subsequent exacerbation after remission 7
• Periodic evaluation of symptoms, serum total IgE, and chest imaging to detect early recurrence 7
• Early identification and treatment crucial to prevent progression to irreversible bronchiectasis and fibrosis 1

Monitoring for ABPA-CPF Progression

• ABPA-CPF diagnosed when two or more features present: pulmonary fibrosis, fibro-cavitary lesions, fungal ball, or pleural thickening 2
• Even in fibrotic stage, total IgE ≥500 IU/mL and A. fumigatus-specific IgE remain mandatory for diagnosis (IgE may be lower in end-stage fibrosis) 2
• Oral corticosteroids remain cornerstone even in fibrotic stage to control ongoing allergic inflammation 2

Common Monitoring Pitfalls

• Pitfall: Relying on chest X-ray alone for initial diagnosis—obtain HRCT because X-ray normal in ~50% of cases 6
• Pitfall: Excessive radiation from repeated CT—use radiographs for routine follow-up 6
• Pitfall: Missing high-attenuation mucus—always review mediastinal windows 6
• Pitfall: Using blood eosinophil count to assess treatment response—not validated 7

8. Key Clinical Recommendations Summary

Early diagnosis and treatment of ABPA before development of bronchiectasis and fibrosis is crucial to prevent irreversible lung damage and improve long-term outcomes. 1

• ABPA is an asthma endotype that responds exceptionally well to specific therapy 1
• Systematic screening for A. fumigatus sensitization recommended in all newly diagnosed adult asthmatics at tertiary centers and difficult-to-treat asthmatic children 1
• The 2024 ISHAM guidelines lowered total IgE threshold to ≥500 IU/mL for improved sensitivity 1
• High-attenuation mucus on CT is pathognomonic with 100% specificity 6
• Monotherapy (prednisolone OR itraconazole) for initial/infrequent exacerbations; combination therapy reserved for recurrent disease 7
• Do not treat asymptomatic ABPA 7
• Use chest radiographs for routine monitoring; reserve CT for complications 6
• Multidimensional response criteria (symptoms, IgE, imaging, FEV₁) at 8–12 weeks guide treatment success 7
• Approximately 50% of patients experience recurrence; high-risk patients (≥2 exacerbations in 1–2 years) require early combination therapy 7