What is ABPA (Allergic Bronchopulmonary Aspergillosis)?
ABPA is a complex hypersensitivity lung disease caused by an exaggerated immune reaction to Aspergillus fumigatus colonizing the airways, primarily affecting patients with asthma or cystic fibrosis, and requires prompt recognition to prevent irreversible bronchiectasis. 1
Core Pathophysiology
ABPA represents a type I hypersensitivity reaction where Aspergillus fumigatus grows within the airways, triggering dysregulated type 2 immune responses with markedly elevated IgE levels, peripheral eosinophilia, and chronic inflammation that progressively damages lung tissue 1, 2. Unlike simple fungal sensitization, the fungus actively colonizes the airways, making ABPA a distinct asthma endotype that responds exceptionally well to specific therapy 1.
Diagnostic Criteria (2024 ISHAM Guidelines)
To diagnose ABPA, you must demonstrate:
Mandatory Requirements:
- Predisposing condition (asthma, cystic fibrosis, or compatible clinical presentation)
- Aspergillus fumigatus-specific IgE ≥0.35 kUA/L (fungal sensitization)
- Serum total IgE ≥500 IU/mL (immunological activity) 1
Plus TWO of the following:
- A. fumigatus-specific IgG elevation
- Peripheral blood eosinophils ≥500 cells/μL
- Suggestive imaging findings 1
Critical imaging finding: High-attenuation mucus (HAM) on CT is pathognomonic and can diagnose ABPA even when other criteria are incomplete 1.
Clinical Presentation
Patients typically present with:
- Uncontrolled asthma symptoms (chronic cough, wheezing, dyspnea)
- Expectoration of brownish mucus plugs (characteristic symptom) 3
- Fleeting pulmonary infiltrates on chest X-ray
- Progressive bronchiectasis if untreated 3
Common pitfall: 69% of ABPA patients are initially misdiagnosed, with 21% incorrectly treated for tuberculosis due to overlapping radiological features 4. This is particularly problematic in TB-endemic regions.
Radiological Classification (2024 ISHAM)
The disease is staged by CT findings 1:
- ABPA-S: Serological only (no bronchiectasis)
- ABPA-B: With bronchiectasis
- ABPA-MP: With mucus plugging (indicates greater immunological severity)
- ABPA-HAM: With high-attenuation mucus (pathognomonic)
- ABPA-CPF: With chronic pleuropulmonary fibrosis
Your Patient's Specific Situation
For a patient with known Aspergillus hypersensitivity recently re-exposed to mold presenting only with internal shivering, normal oxygen saturation, and normal blood pressure:
This presentation is atypical and non-specific for ABPA. Internal shivering alone with normal vital signs does not suggest acute ABPA exacerbation, which typically manifests with respiratory symptoms (increased cough, wheezing, dyspnea, mucus production) 1.
Recommended Workup:
- Measure serum total IgE immediately - compare to baseline if available
- Check peripheral blood eosinophil count
- Obtain chest imaging (chest X-ray initially; CT if abnormal or high suspicion)
- Assess pulmonary function if symptomatic
- Measure A. fumigatus-specific IgE and IgG 1
Management Decision Algorithm:
If asymptomatic with stable imaging and IgE: Do NOT treat routinely - observation is recommended 1
If symptomatic (respiratory symptoms develop) OR rising IgE OR new radiological changes:
- First-line: Oral prednisolone OR itraconazole monotherapy 1
- Recurrent exacerbations: Combination prednisolone + itraconazole 1
Critical caveat: The symptom of "internal shivering" alone does not meet criteria for treating ABPA. This could represent:
- Anxiety related to mold re-exposure
- Unrelated systemic illness requiring separate evaluation
- Early constitutional symptoms requiring close monitoring
Monitor this patient closely over 48-72 hours for development of respiratory symptoms, and obtain baseline laboratory and imaging studies to establish whether ABPA is present or has progressed. If respiratory symptoms emerge, initiate treatment promptly as early intervention prevents bronchiectasis progression 1.