Aspergillus-associated hypersensitivity respiratory disorders

The mould Aspergillus is responsible for a gamut of respiratory diseases ranging from saprobic colonisation to rapidly invasive disseminated disease. The clinical spectrum of Aspergillus-associated hypersensitivity respiratory disorders includes Aspergillus induced asthma, allergic bronchopulmonary aspergillosis (ABPA), allergic Aspergillus sinusitis (AAS) and hypersensitivity pneumonitis. Inhalant allergens, in patients with allergic asthma, play a key role in bringing about the inflammation present in the airways, and fungi are increasingly being recognised as important inhalant allergens. Aspergillus is linked to asthma in more ways than one. In the asthmatic subjects, the fungal spores are trapped in the thick and viscid secretions that are usually present in the airways. This generally develops in atopic subjects and is sustained by continuous inhalation of Aspergillus antigens, triggering asthma that may be more severe in form. Aspergillus induced asthma is yet to receive the recognition that it deserves. Allergic bronchopulmonary aspergillosis is the best known form of allergic aspergillosis and is an emerging disease in India. An immunologically mediated lung disease, ABPA occurs predominantly in patients with asthma. A set of diagnostic criteria is required as there is no single test that establishes the diagnosis apart from demonstration of central bronchiectasis with normal tapering bronchi, a feature considered to be pathognomonic of ABPA. Radiologically, ABPA is characterised by 'transient pulmonary infiltrates' or 'fleeting shadows', often confused with pulmonary tuberculosis. A comparatively more recently recognised clinical entity, AAS is characterised by mucoid impaction in the paranasal sinuses which is akin to that in ABPA. Although it appears that the patient with ABPA provides a favourable milieu for the occurrence of AAS, it is perhaps surprising that in spite of similar histopathological features the co-existence of both these diseases has not often been reported. Aspergilloma, a fungal ball that appears in a pre-existing cavity due to saprobic colonisation of Aspergillus species, can often present with asthma. The association of ABPA and aspergilloma is also known. Although cavitation can occur in ABPA, the co-existence of ABPA with aspergilloma is rather uncommon. Aspergillomas may function as a nidus for antigenic stimulation in a genetically predisposed individual resulting in the occurrence of ABPA. Contemporaneous occurrence of ABPA, AAS and aspergilloma has also been reported. Screening all asthmatic subjects for Aspergillus sensitisation could identify those with a severe form of the disease as well as those at risk for developing ABPA. Furthermore, concomitant occurrence of ABPA and AAS is now being increasingly recognised, and AAS must be excluded in all patients with ABPA.