Understanding Allergic Bronchopulmonary Aspergillosis (ABPA)
A/Prof David Serisier, Director, Mater Hospital Adult Respiratory Medicine Department and Chair, Lung Foundation Australia Board
Allergic bronchopulmonary aspergillosis (ABPA) is a disease of the airways in the lungs that occurs in response to the presence of a fungus called Aspergillus. There are many different types of Aspergillus, but Aspergillus fumigatus is the most common to cause disease in humans. Aspergillus
is very common in the environment and can exist in microscopic form in the air. Therefore, it can be easily inhaled into the lungs but does not necessarily result in any disease in most individuals. However certain individuals, usually with some type of ‘predisposition’, can develop a disease as a result of Aspergillus being present in the airways.
There are, broadly, three general types of disease that can result when Aspergillus comes into contact with the airways (see Figure 1):
- Infection of the lung tissue, termed ‘invasive aspergillosis’, is when the Aspergillus invades beyond the airway walls into the lung tissue itself in order to cause infection. This disease ordinarily only occurs in people with very significant problems of their immune system.
- Infections occurring within an abnormal lung, but without invasion beyond the airways (e.g. ‘fungal ball’ in the lung). This disease usually occurs when the lung structure is not normal, such as a cavity in the lung from a previous severe or destructive infection such as tuberculosis.
- An allergic reaction within the airways and lungs to the presence of the fungus, one version of which is ABPA. This form of aspergillus-related disease occurs in individuals who are ‘atopic’ or prone to allergy, particularly those with asthma.
ABPA is a type of allergic or hypersensitivity response to the presence of Aspergillus within the airways. It occurs mainly in people with asthma, and is often associated with asthma that is difficult to control. People experience worsening asthma symptoms with increased wheezing, coughing up sputum occasionally with brown-coloured mucus ‘plugs’ and may experience fever. Some people experience more frequent asthma attacks needing treatment with systemic corticosteroids (prednisone). A chest x-ray may be abnormal and may look the same as the chest x-ray of someone with ‘pneumonia’ (but pneumonia is a different condition due to infection of the lung with other bugs). Often these x-ray changes can be ‘fleeting’ or come and go.
The diagnosis of ABPA requires the presence of a constellation of symptoms, x-ray abnormalities and investigation results that provide evidence of the presence of sensitisation to Aspergillus as well as a ‘response’ by the body to the fungus. Evidence of allergic sensitisation can be shown on blood and skin prick tests. Simply finding Aspergillus in a sputum culture does not necessarily mean that there is any form of disease due to Aspergillus (including ABPA), although it is often found in those with ABPA.
ABPA can be divided into five stages, however these are not necessarily sequential phases of the disease and the condition can be first diagnosed at any one of the stages. They are:
- Corticosteroid dependent asthma
- End-stage (fibrotic).
The stages are all reversible except for stage five (fibrotic). ABPA can also result in a condition called bronchiectasis, and may cause lung cavities.
Treatment of ABPA is based around the concepts of either suppressing the airway hypersensitivity response to the fungus and/or trying to reduce the amount of fungus present in the airways thereby reducing the ‘stimulus’ to the allergic response. It is critical that patients with asthma are appropriately taking sufficient doses of inhaled corticosteroids (‘preventer’ puffers) each day to reduce airway inflammation and irritation. This alone may be sufficient to control ABPA in some people. Usually though, patients will also require systemic corticosteroids (e.g. prednisone) to treat an ABPA flare up. It is advisable to try to limit the use of systemic steroids as much as possible due to long-term side effects that often occur. The intensity and duration of treatment needs to be individualised by your doctor. Occasionally, patients with severe disease may actually need to stay on corticosteroids permanently, although efforts to avoid this are preferable.
Therapies to try to reduce the amount of fungus within the airway involve taking antifungal agents (e.g. itraconazole). These drugs often improve ABPA control and may enable people on corticosteroids to reduce their dose. The duration of therapy with an antifungal agent also needs to be individualised with your doctor according to a variety of factors including response to the treatment, the severity of the ABPA, whether you are on long-term corticosteroids, etc. In some people, antifungals will become a permanent treatment. Antifungals can have major interactions with other medicines and needs to be carefully considered when prescribing.
Omalizumab, an expensive injectable antibody that blocks part of the body’s allergic immune response, has been shown to be effective in a certain subgroup of asthma patients. It has been used experimentally in some patients with ABPA, and may turn out to be a useful therapy for this condition in the future, although further research is needed.