Allergic bronchopulmonary aspergillosis

Overview
Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity response to the fungus Aspergillus fumigatus, the spores of which are ubiquitous in soil and are commonly found in the sputum of healthy individuals. A. fumigatus is responsible for a spectrum of lung diseases commonly grouped under the heading of aspergilloses.

Epidemiology
Estimating the prevalence of ABPA has been made difficult by lack of uniform diagnostic criteria and standardised tests. It usually occurs as a complication of other chronic lung disease, in particular asthma or cystic fibrosis. It is estimated that in the US ABPA may be present in between 0.5 and 2% of all asthma patients.

Immunology and pathophysiology
There is both a type I (atopic) and type III hypersensitivity response. Precipitating antibodies incite a type I acute hypersensitivity reaction with release of immunoglobulin E (IgE) and immunoglobulin G (IgG), resulting in mast cell degranulation with bronchoconstriction and increased capillary permeability. Immune complexes and inflammatory cells are then deposited within the bronchial mucosa leading to tissue necrosis and eosinophilic infiltrate, a type III reaction. The subsequent damage to the bronchial wall causes (proximal) bronchiectasis. Repeated acute episodes left untreated can result in progressive pulmonary fibrosis that is often seen in the upper zones and can give rise to a similar radiological appearance to that produced by tuberculosis.

The main features are therefore:
 * bronchospasm
 * increased mucus production and plugging of distal airways, leading to their collapse
 * bronchiectasis

Symptoms

 * wheeze
 * cough
 * fever
 * malaise
 * recurrent pneumonia (eosinophilic, therefore not responding to antibiotics)
 * expectoration of mucoid plugs (containing the fungal hyphae)
 * unexplained worsening of asthma or cystic fibrosis

Investigations
A full blood count usually reveals eosinophilia more than 10% and there is a raised serum IgE more than 1000ng/ml.

Chest radiography shows various transient abnormalities: Aspergillus specific tests:
 * consolidation or collapse
 * thickened bronchial wall markings
 * peripheral shadows
 * signs of central bronchiectasis
 * precipitating antibodies to aspergillus species in >90% of cases
 * aspergillus-specific IgE RAST test
 * skin-prick test is almost always positive to Aspergillus fumigatus

Management
The aim of treatment is to suppress the immune reaction to the fungus and to control bronchospasm.

The immune reaction is suppressed using oral corticosteroids:
 * a high dose of prednisolone or prednisone (30 to 45 mg per day) in acute attacks
 * a lower maintenance dose (5-10 mg per day)

Mucus plugs may be removed by bronchoscopic aspiration. It is almost impossible to eradicate the fungus but sometimes itraconazole (an anti-fungal) is used in combination with steroid therapy. Regular monitoring of the condition includes chest x-rays, pulmonary function tests, and serum IgE. The antibody levels usually fall as the disease is controlled, but they may rise again as an early sign of flare-ups.

Related Chapters

 * Aspergillosis
 * Asthma
 * Cystic fibrosis
 * Bronchiectasis