Allergic bronchopulmonary aspergillosis
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In medicine, allergic bronchopulmonary aspergillosis (ABPA) is a condition characterised by an exagerated response of the immune system (a hypersensitivity response) to the fungus Aspergillus (most commonly Aspergillus fumigatus). It occurs most often in patients with asthma or cystic fibrosis. Aspergillus spores are ubiquitous in soil and are commonly found in the sputum of healthy individuals. A. fumigatus is responsible for a spectrum of lung diseases known as aspergilloses.

ABPA causes airway inflammation which can ultimately be complicated by sacs of the airways (bronchiectasis). The disease may cause airway constriction (bronchospasm). Besides asthma and cystic fibrosis, ABPA can also resemble other conditions such as eosinophilic pneumonia.

The exact criteria for the diagnosis of ABPA are not agreed upon. Chest X-rays and CT scans, raised blood levels of IgE and eosinophils, immunological tests for Aspergillus together with sputum staining and sputum cultures can be useful. Biopsies are rarely needed. Treatment consists of corticosteroids and antifungal medications.

Symptoms

Patients with allergic bronchopulmonary aspergillosis often have symptoms of poorly controlled asthma, with wheezing, cough, shortness of breath and exercise intolerance. They also have symptoms reminding of bronchiectasis, such as chronic sputum production, coughing up brownish mucoid plugs or even blood (the latter is called hemoptysis), and recurrent infections (with fever and malaise). However, since the infiltrates in ABPA indicate eosinophilic pneumonia, they do not respond to treatment with antibiotics. There may be unexplained worsening of asthma or cystic fibrosis.

Diagnosis

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:

• consolidation, infiltrates or collapse
• thickened bronchial wall markings
• peripheral shadows
• signs of bronchiectasis, typically in a central location

Aspergillus specific tests:

• precipitating antibodies to aspergillus species in >90% of cases
• aspergillus-specific IgE RAST test
• skin-prick test is almost always positive to Aspergillus fumigatus

Fungal hyphae may be seen in the sputum.

Treatment

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.

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 ABPA may be present in between 0.5 and 2% of all asthma patients, and in between 1 and 15% of cystic fibrosis patients.^[1]

Disease mechanism

For an unknown reason, patients with allergic bronchopulmonary aspergillosis develop a hypersensitivity response, both a type I response (atopic, with formation of immunoglobulin E or IgE) and a type III hypersensitivity response (with formation of immunoglobulin G or IgG). The reaction of immunoglobulin E with Aspergillus antigens results in mast cell degranulation with bronchoconstriction and increased capillary permeability. Immune complexes (a type III reaction) and inflammatory cells are then deposited within the mucous membranes of the airways, leading to necrosis (tissue death) and an eosinophilic infiltrate. Type 2 T helper cells secreting interleukin 4 and interleukin 5, and attraction of neutrophils by interleukin 8 seem to play an important role.

In spite of this pronounced immune reaction, the fungus is not cleared from the airways. The subsequent damage to the bronchial wall caused by proteolytic enzymes released by the immune cells and toxins released by the fungi results in bronchiectasis, most pronounced in the central parts of the airways. 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.

This model explains the main features of episodic bronchospasm, increased mucus production and plugging of distal airways, leading to their collapse and subsequent bronchiectasis.

References

• Kumar, Parveen (1998). Clinical Medicine. Philadelphia: W.B. Saunders. ISBN 0702020192. 
• Longmore, Murray (2004). Oxford Handbook of Clinical Medicine. Oxford Oxfordshire: Oxford University Press. ISBN 0198525583. 
• Greenberger PA, Patterson R (1988). "Allergic bronchopulmonary aspergillosis and the evaluation of the patient with asthma". J. Allergy Clin. Immunol. 81 (4): 646-50. PMID 3356845. 
• V.P.Kurup, B.Banerjee, P.A.Greenberger, J.N.Fink. Allergic Bronchopulmonary Aspergillosis: Challenges in Diagnosis. From Medscape General Medicine. full text

Footnotes

1. ^ Stevens DA, Moss RB, Kurup VP, et al (October 2003). "Allergic bronchopulmonary aspergillosis in cystic fibrosis--state of the art: Cystic Fibrosis Foundation Consensus Conference". Clin. Infect. Dis. 37 Suppl 3: S225–64. PMID 12975753. 

External links

• Allergic Bronchopulmonary Aspergillosis - GP Notebook
• Allergic Bronchopulmonary Aspergillosis - The Merck Manuals Online Medical Library
• Medpix. ABPA radiology pictures