Allergic bronchopulmonary aspergillosis (ABPA)

• Incidence
• Predisposing Factors
• Microscopic Features
• Natural History
• Clinical History
• Clinical Examination
• General Investigation
• Specific Investigations
• Prognosis
• Treatment Overview
• References

Incidence

Allergic bronchopulmonary aspergillosis (ABPA) was first reported in England in 1952. Since then, a number of cases have been diagnosed in numerous countries. The incidence of ABPA in asthmatics varies from 3.7-11% in Western countries; while in India, there have been reports of incidence rates as high as 15% in cases of perennial asthmatics.² A recent study suggested that the prevalence of ABPA in patients with chronic bronchial asthma is as high as 16%.

Predisposing Factors

Asthma is a criterion for diagnosing this condition as this disease only occurs in asthmatics. Otherwise, aspergillosis affects all races, gender, and age equally.

Microscopic Features

Histopathologically, bronchial plugs can be seen in ABPA, which are composed of degenerating eosinophils mixed with Aspergillus hyphae. If bronchiectasis occurs, the proximal bronchi will be observed to be dilated but the distal bronchi normal – hence the term saccular bronchiectasis.

Natural History

The pathophysiology of ABPA is not completely understood. However, it is known to involve an allergic reaction to the fungus Aspergillus spp. Chronic respiratory conditions such as asthma and cystic fibrosis may trap Aspergillus fumigatus in the persistent secretions. The body responds by mounting an immune reaction towards Aspergillus.
Later, chronic colonisation by Aspergillus causes increased IgG and IgE levels, leading to recurrent bronchospasm and symptom production. It is interesting to note that despite vigorous immune responses towards Aspergillus, the fungus is still able to colonise the airway and cause recurrent symptoms.
Chronic colonisation by Aspergillus eventually leads to proteolytic enzymes and mycotoxin release by the fungi. Added with chronic eosinophilic inflammation, the end result is airway damage and central bronchiectasis. The natural history of this disease includes chronic exacerbations and remissions.

Clinical History

The patient with ABPA can be difficult to diagnose. Common presentations include typical asthma symptoms, such as wheezing, difficulty breathing, fever, feeling unwell and excessive coughing at night.
Sometimes, bloody or brownish-yellow phlegm production occurs. This may lead to the diagnosis of bacterial pneumonia (infection of the lungs) at first. It is important to suspect this diagnosis if the patient with previous history of asthma complains of cough productive of yellow or blood-stained phlegm.

Clinical Examination

A general physical examination should be carried out. As this disease primarily affects the lungs, a complete lung examination will be required. Clinical findings are usually consistent with an acute asthma attack associated with an infection. These include fever, shortness of breath, increased breathing rate and increased heart rate. Specifically, positive lung findings include wheezing, the presence of bubbly sounds on inspiration during auscultation, and dullness on chest percussion.

General Investigations

If the presenting condition is severe enough to require hospital treatment or even admission, the following routine tests will be done:

• Full blood count;
• Liver function test;
• Renal function test;
• Electrolytes.

There may be abnormalities in the white cell count, consistent with an infection. Otherwise, the remaining results are usually normal.

Specific Investigations

An early diagnosis is important because the earlier the detection, the better the chances of treatment. Early diagnosis can also reduce the risk of complications, such as lung fibrosis.
Whilst there is no individual test to establish the diagnosis of ABPA, the following tests can be done:

• Skin prick test: this should be the first step in an asthmatic being evaluated for the possibility of ABPA. This involves injecting allergen (substances that induce allergy) and evaluate if there is any immune reaction towards the allergen that contains Aspergillus protein.
• Serum IgE level: IgE is an antibody that is raised in this disease because it is responsible for the allergic component of this disease. The total IgE concentration of > 1,000 ng/mL can be used as a diagnostic feature of ABPA.
• Serum eosinophil level: eosinophil is a white blood cell that is raised in allergic reactions. Increased blood level of eosinophil can be used as a diagnostic feature of ABPA.
• Sputum culture: this means collection of the phlegm (sputum) for culture of the fungi. A positive culture indicates the presence of infection or colonisation, but not the allergic component of this disease.
• Other tests for Aspergillus infection: serology can be done to confirm previous aspergillus infection

Lung function tests can be done to assess the severity of the disease. Imaging studies such as chest X-ray and/or high resolution CT scan should be obtained to detect any lung changes for this disease. Sometimes the windpipes (bronchi) can be dilated – this is known as bronchiectasis.

Prognosis

In many patients, the disease consists of recurrent attacks that are minimally symptomatic. However, progression to respiratory failure may occur as a result of irreversible airway destruction. The exact statistical prognosis remains unknown.

Treatment Overview

There is no cure for the disease. The treatment aims are to control acute inflammatory exacerbations and to limit progressive lung disease. The following are the possible treatment options:

• Corticosteroids: these are very effective in suppressing inflammation in ABPA. However, if given long term, they can have significant side effects and therefore should only be given under medical supervision.
• Itraconazole: antifungal agents are not generally recommended; however, several studies suggest its use could be beneficial in patients with ABPA. A randomised double-blind trial concluded that the addition of itraconazole to corticosteroids for 16 weeks was associated with a significant increase in clinical response (46% compared to 19% of patients already on corticosteroids).³

References

1. Batra V, Asmar B, Ang JY. Aspergillosis [online]. Omaha, NE: eMedicine; 2005 [cited 15 October 2005]. Available from: URL link
2. Kumar R. Mild, moderate, and severe forms of allergic bronchopulmonary aspergillosis: A clinical and serologic evaluation. Chest. 2003;124(3): 890-2. [Abstract| Full text]
3. Stevens DA, Schwartz HJ, Lee JY, et al. A randomized trial of itraconazole in allergic bronchopulmonary aspergillosis.N Engl J Med. 2000;342(11):756-62. [Abstract | Full text]
4. Akuthota P, Weller PF. Allergic bronchopulmonary aspergillosis [online]. Waltham, MA: UpToDate; 2005 [cited 15 October 2005]. Available from: URL link