Allergic Bronchopulmonary aspergillosis (ABPA) is a fungal infection of the lungs that causes a hypersensitivity reaction to multiple antigens expressed by Aspergillus fumigatus. Aspergillus fumigatus spores are only 2 to 3 micrometers in diameter and can easily colonize pulmonary alveoli. ABPA primarily affects patients with uncontrolled asthma, cystic fibrosis, and immunosuppression. Thick mucus in the airways of these patients makes it difficult to clear these spores after they are inhaled.
The prevalence of ABPA in asthma and cystic fibrosis is about 13% and 9%, respectively. Worldwide, more than 4 million people are affected by ABPA.
Symptoms of ABPA usually appear during the third to fifth decades of life and range from acute, recurrent asthma exacerbations with wheeze, cough, and lung infiltrates to generalized systemic features of fever, anorexia, headache and malaise. Sputum production is characterized by solid chunks of green to beige colored plugs.
Biopsies show chronic bronchial inflammation with eosinophilia, airway remodeling and bronchiectasis. Bronchi may contain mucus plugs with fungal hyphae, Charcot-Leyden crystals, and Curschmann spirals.
The most common diagnostic modality is an Aspergillus skin test for immediate cutaneous hypersensitivity to Aspergillus fumigatus. Laboratory tests are also helpful. Patients, who are not taking oral or inhaled corticosteroids, often have peripheral blood eosinophil counts higher than 1 x 106/uL per uL. Detecting elevated levels of specific serum IgE to Aspergillus fumigatus is the hallmark of diagnosis. The total IgE serum level is elevated to higher than 1000 ng/mL and often may reach levels >10,000. A normal level in a symptomatic patient can exclude the diagnosis of ABPA, especially if Aspergillus fumigatus specific IgE levels are not elevated. Total serum IgE level is also an important tool to follow patients over time. The level fluctuates with exacerbations and remissions and should fall to baseline when a patient is in remission.
Culture of AF in the sputum is supportive but not diagnostic of ABPA. However, if sputum cultures are positive in patients with longstanding, refractory, corticosteroid dependent asthma, further immunologic testing to exclude the diagnosis of ABPA is required. Culture is helpful in determining antibiotic susceptibility.
References
Agarwal R et al. Developments in the diagnosis and treatment of allergic bronchopulmonary aspergillosis. Expert Rev Respir Med. 2016 Dec;10(12):1317-1334.
Shah A, Panjabi C. Allergic Bronchopulmonary Aspergillosis: A Perplexing Clinical Entity. Allergy Asthma Immunol Res. 2016 Jul;8(4):282-97.
Vlahakis NE, Aksamit TR. Diagnosis and treatment of allergic bronchopulmonary aspergillosis. Mayo Clin Proc. 2001 Sep;76(9):930-8.
Gibson PG. Allergic bronchopulmonary aspergillosis. Semin Respir Crit Care Med. 2006 Apr;27(2):185-91
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