Allergic Bronchopulmonary Aspergillosis
Allergic bronchopulmonary aspergillosis (ABPA) is a chronic pulmonary eosinophilic hypersensitivity reaction resulting in airflow obstruction and bronchiectasis. Disease results from an exaggerated allergic response to several fungal species, particularly Aspergillus fumigatus, which accounts for nearly 90% of cases. The exact mechanism is unknown; however, several host factors and specific IgE-mediated type-I, IgG-mediated type-III, and (under investigation) cell-mediated type-IV hypersensitivity reactions are thought to contribute to the pathogenesis of this disorder.

First described by Hinson and colleagues in 1952, ABPA is a disease nearly exclusively seen in those with underlying obstructive or bronchiectatic airways disorders. Among those with asthma, a recent epidemiologic study by Novey and colleagues estimated that ABPA occurs between 0.25% and 11%. However, the reported prevalence of ABPA in this population has varied widely and may be greater than 20% among those with poorly controlled asthma ( Table 1 ).

While asthma is the most common and best understood contributing factor, ABPA is also prominent among those with cystic fibrosis and other underlying bronchiectatic diseases. The reported prevalence of ABPA among those with cystic fibrosis also varies and is estimated to occur in 1%-15% of patients. Although less described, other associated conditions include allergic rhinitis, allergic fungal sinusitis, bronchocentric granulomatosis, atopic dermatitis, and contact dermatitis. A familial occurrence pattern has been described but is not well understood. Associations with hyper-IgE syndrome and chronic granulomatous diseases have been described. These underlying etiologies are important to identify because concurrent steroid treatment may precipitate invasive fungal infections.

The difficulty in establishing the true prevalence of ABPA is likely multifactorial. Clinical presentations vary and are nonspecific. Symptoms may present in childhood, while others may remain asymptomatic for decades. There is no true age of distribution; however, disease may present more commonly in the fifth and sixth decades. However, it has been reported in both extremes of life, including patients younger than 1 to 2 years of age. Although asthma is a cardinal feature of ABPA, its severity varies greatly. The majority of patients experience long-standing, often difficult-to-control asthma while others may experience mild symptoms or even remain relatively asymptomatic. Additionally, the lack of consensus regarding diagnostic criteria further contributes to the difficulty in identifying this disorder and establishing its true prevalence.