Allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is at one end of the spectrum of disease caused by pulmonary aspergillosis and can be classified as an eosinophilic lung disease ^2-4.

Epidemiology

This entity is seen is almost only encountered in patients with long standing asthma, and only occasionally in patients with cystic fibrosis ^4-5.  Only rarely does it appear in patients with no other identifiable pulmonary illness ⁵. 

In general patients are young and are diagnosed before the age of 40 years ⁹.

Clinical presentation

Clinically, patients have atopic symptoms (especially asthma) and present with recurrent chest infection. They may expectorate orange-coloured mucous plugs.

A clinical staging system has been developed ⁹:

• stage I : acute
• stage II : remission
• stage III : recurrent exacerbation
• stage IV : steroid-dependent asthma
• stage V : pulmonary fibrosis

Laboratory findings include :

• elevated Aspergillus specific IgE
• elevated precipitating IgG against Aspergillus
• peripheral eosinophilia
• positive skin test

Major and minor criteria have also been established ^5-6.

• major criteria
  • clinical
    • asthma
  • radiographic features
    • pulmonary opacities (transient or chronic)
    • central bronchiectasis
  • immune system
    • blood eosinophilia
    • immediate skin reactivity to Aspergillus antigen
    • increased serum IgE
• minor criteria
  • fungal elements in sputum
  • expectoration of brown plugs / flecks
  • delayed skin reactivity to fungal antigens

Pathology

Allergic bronchopulmonary aspergillosis (ABPA) is the result of hypersensitivity towards Aspergillus spp which grows within the lumen of the bronchi, without invasion. The hypersensitivity initially causes bronchospasm and bronchial wall oedema, which is IgE-mediated. Ultimately, there is bronchial wall damage with loss of muscle and bronchial wall cartilage resulting in bronchiectasis (typically central bronchiectasis) ⁷. Both type I and type III allergic reactions have been implicated ⁴.

Segmental and subsegmental bronchi are dilated and filled with mucous, admixed with eosinophils and occasional fungal hyphae ^4,7. Charcot-Leyden crystals may be prominent ⁷. Macroscopically, the mucous plugs are orange / brown in colour.

Radiographic features

Plain film

Early in the disease chest x-rays will appear normal, or only demonstrate changes of asthma. Transient patchy areas of consolidation may be evident representing eosinophilic pneumonia. 

Eventually bronchiectasis may be evident. Mucoid impaction in dilated bronchi can appear mass-like or sausage shaped or branching opacities.

CT 

CT findings include :

• fleeting pulmonary alveolar opacities : common
• centrilobular nodules representing dilated and opacified bronchioles⁴
• bronchiectasis
  • central, upper lobe saccular bronchiectasis is characteristic
  • mucoid impaction results in a bronchocoele - finger in glove sign 
  • this may give a Y, V or toothpaste-like like configuration.
  • high attenuation in impacted mucus in ≈ 30 % ^3-4
  • bronchial wall thickening : common
• chronic disease may progress to pulmonary fibrosis, predominantly in upper lobe
• cavitation : 10%

Treatment and prognosis

Treatment of ABPA is difficult due to the ubiquity of Aspergillus in the environment. The main focus of treatment revolves around ⁸: 

• managing asthma
• limiting / controlling exacerbations : corticosteroid play a major role
• eradicating Aspergillus from the airway : anti-fungals e.g. Ketoconazole
• preventing late complications e.g. severe bronchiectasis and fibrosis

Many patients are successfully managed after diagnosis and never progress to stage IV or V. In stages I to III prognosis is excellent, whereas stage V has a high 5 year mortality from respiratory failure ⁹.

Differential diagnosis

For a discussion of the differential diagnosis of bronchiectasis please refer to the article bronchiectasis and more specifically central bronchiectasis. 

For mucoid impaction consider:

• mucoid impaction secondary to bronchiectasis
• secondary to endobronchial lesion
• secondary to atretic bronchial segment