Key Facts

Allergic bronchopulmonary aspergillosis (ABPA) is an immunologically mediated lung disease caused by hypersensitivity to Aspergillus fumigatus colonising the airways. It is characterised by eosinophilic inflammation, mucus plugging, and progressive bronchiectasis if untreated.

Epidemiology

ABPA affects 1-2% of persistent asthmatics and 2-15% of cystic fibrosis patients. It is rare without underlying airways disease. Peak incidence is in the 3rd-4th decades. Both sexes are equally affected. Sensitisation to Aspergillus (positive skin prick or specific IgE) is present in ~25% of asthmatics, but only a minority develop ABPA.

Aetiology

Aspergillus fumigatus spores (2-3 μm diameter) are ubiquitous in the environment and inhaled into the lower airways. In susceptible individuals with impaired mucociliary clearance (asthma, CF), spores germinate and hyphae colonise the bronchial mucus. The immune response involves:

• Type I hypersensitivity: IgE-mediated mast cell degranulation → immediate bronchospasm
• Type III hypersensitivity: IgG immune complex deposition → complement activation → inflammation
• Type IV: T-cell mediated response contributing to chronic inflammation

Pathophysiology

The combined hypersensitivity response causes intense eosinophilic airway inflammation, mucus hypersecretion with mucus plugging, and bronchial wall damage. Mucus plugs contain eosinophils, Charcot-Leyden crystals, and Aspergillus hyphae. Chronic inflammation leads to central (proximal) bronchiectasis — a hallmark of ABPA. If untreated, progressive fibrosis and end-stage lung destruction occur.

Typical Presentation

• Poorly controlled asthma despite adequate treatment — recurrent exacerbations, increased steroid requirement
• Productive cough with brown/golden mucus plugs (sometimes with branching casts)
• Episodic wheeze, dyspnoea, and fever
• Fleeting pulmonary infiltrates on serial CXR ("pulmonary eosinophilia")

CF Patients

• Declining lung function despite optimal CF care
• Increased sputum production and mucus plugging
• New infiltrates on CXR

Red Flags

• Rapidly progressive dyspnoea (consider invasive aspergillosis if immunocompromised)
• Haemoptysis (bronchiectasis-related, or consider aspergilloma)
• Weight loss (consider chronic infection, malignancy)
• Fixed airflow obstruction despite treatment (progressive bronchiectasis/fibrosis)

Bedside

• Skin prick test to Aspergillus fumigatus: immediate (Type I) positivity
• Sputum examination: eosinophils, Aspergillus hyphae on microscopy/culture
• Peak flow monitoring: variability

Bloods

• Total serum IgE: typically >1000 IU/mL (often >2000); essential for monitoring
• Aspergillus-specific IgE (RAST): raised
• Aspergillus-specific IgG (precipitins): positive in >90%
• FBC: peripheral eosinophilia (>0.5 × 10⁹/L, often >1.0)
• CRP/ESR: may be raised during exacerbations

Imaging

• CXR: fleeting infiltrates, tramline shadows (bronchiectasis), finger-in-glove opacities (mucus plugging)
• HRCT thorax: central (proximal) bronchiectasis (predominantly upper lobes), high-attenuation mucus plugging (pathognomonic), tree-in-bud opacities, mosaic attenuation

Special Tests

• Spirometry: obstructive pattern (asthma) ± fixed airflow obstruction; may have mixed obstructive-restrictive if fibrotic
• DLCO: may be reduced in advanced fibrotic ABPA
• Bronchoscopy + BAL: eosinophilia, Aspergillus culture, mucus plug removal

Non-pharmacological

• Environmental measures: reduce mould/damp exposure where possible (though Aspergillus is ubiquitous)
• Airway clearance techniques: particularly in CF patients — physiotherapy, mucolytic devices
• Pulmonary rehabilitation: if chronic lung function impairment

Pharmacological

• Acute/flare: prednisolone 0.5 mg/kg/day for 2 weeks, then 0.5 mg/kg on alternate days for 6-8 weeks, then taper over 3-6 months; total duration typically 3-6 months
• Itraconazole 200 mg BD for 16 weeks as steroid-sparing adjunct — reduces relapse rate and steroid requirement (monitor LFTs and itraconazole levels; target trough >0.5 mg/L)
• Voriconazole 200 mg BD: second-line if itraconazole ineffective/not tolerated
• Optimise asthma therapy: ICS/LABA, consider biologic therapy
• Omalizumab (anti-IgE monoclonal): emerging role as steroid-sparing in ABPA; case series show benefit but not licensed specifically for ABPA
• Mepolizumab (anti-IL5): emerging evidence in eosinophilic ABPA

Surgical/Interventional

• Bronchoscopic mucus plug removal: if significant atelectasis from mucus impaction

Referral Criteria

• All cases to respiratory specialist for diagnosis confirmation and management
• Difficult asthma clinic referral if recurrent ABPA flares
• CF MDT involvement for CF-ABPA
• Thoracic surgery if aspergilloma develops with significant haemoptysis

With early diagnosis and treatment, most patients achieve good disease control. Untreated ABPA leads to progressive central bronchiectasis and end-stage fibrotic lung disease (stage V). Relapse rate is ~30-50% during steroid taper. Itraconazole as adjunctive therapy reduces relapse risk. Serial total IgE monitoring (every 6-8 weeks during treatment, then 3-6 monthly) guides therapy — a >35% rise from baseline suggests relapse. In CF patients, ABPA is associated with accelerated lung function decline if inadequately treated.

ABPA Staging (Greenberger/Patterson)

ISHAM-ABPA Diagnostic Criteria